© CLEAPSS 2009
7
Chemicals
CHEMICALS
CONTENTS of this section:
7.1
Section 7 - Page 1
Page
Chemical safety information..................................................................................................... 2
Beware of hearsay................................................................................................................................ 2
Few chemicals are banned but your employer has the final say ......................................................... 2
7.2 Chemical names.....................................................................................................................3
Organic and inorganic chemicals ......................................................................................................... 3
Chemical names and chemical formulae.............................................................................................. 4
7.3 Storage of chemicals .............................................................................................................4
7.3 a Arranging the chemicals by storage category ............................................................................. 4
7.3 b Planning the store........................................................................................................................ 5
7.3 c The particular requirements of each storage category ................................................................ 7
7.3 d Chemicals requiring periodic checks ......................................................................................... 10
7.3 e Stock control .............................................................................................................................. 12
7.3 f Improving the present store........................................................................................................ 13
7.3 g Ventilation in chemical stores .................................................................................................... 17
7.3 h Planning a new chemical store.................................................................................................. 18
7.4 Handling and dispensing large volumes of chemicals ....................................................21
Carrying corrosive liquids ................................................................................................................... 21
Dispensing liquids............................................................................................................................... 22
Transporting chemicals ...................................................................................................................... 22
7.5 Disposal of chemicals .........................................................................................................22
Interpreting the W Hazcard................................................................................................................. 22
Managing chemical waste .................................................................................................................. 25
Some examples of managing the disposal of some commonly used, particular chemicals .............. 26
7.6 Making solutions and reagents ..........................................................................................31
Units encountered when making solutions......................................................................................... 32
Calculations for making solutions of solids......................................................................................... 33
Calculations for making dilute solutions from liquids [eg, sulfuric(VI) acid]........................................ 33
Other units of concentration ............................................................................................................... 34
Saturated solutions ............................................................................................................................. 36
7.7 Dealing with Chemical spills...............................................................................................37
Spills Kits ............................................................................................................................................ 40
General spills kit ................................................................................................................................. 40
Mercury spills...................................................................................................................................... 41
Special procedure for schools without mains drainage ...................................................................... 42
7.8 Chemical hazards ................................................................................................................42
Physico-chemical hazards.................................................................................................................. 43
Health hazards.................................................................................................................................... 45
Environmental hazards ....................................................................................................................... 50
Future hazard classifications .............................................................................................................. 50
7.9 Control of airborne chemical exposure .............................................................................51
Workplace Exposure Limits (WEL)..................................................................................................... 51
Types of contaminants and units used in WELs ................................................................................ 52
Relevance to schools.......................................................................................................................... 52
Odour levels........................................................................................................................................ 53
Measuring WELs in schools ............................................................................................................... 55
Estimation of exposure levels using chemical equations. .................................................................. 56
Appendix 7A
Legal issues affecting storage of chemicals...................................................57
Appendix 7B
Model risk assessment for chemical storage .................................................61
Appendix 7C
Waste disposal, the law and environmental issues .......................................63
Chemicals
7.1
Section 7 - Page 2
© CLEAPSS 2009
Chemical safety information
!It’s important to have accurate and reliable information and advice about the safety of chemicals.
Although such advice may not change very rapidly, the latest edition of any publication should be used
if at all possible. The CLEAPSS Hazcards were revised in 2007 and earlier versions should be thrown
away. The DfEE (now DCSF) publication, Safety in Science Education, includes an extensive list of
chemicals which has been updated by the ASE and is available on its web site1.
The following are useful safety sources that can be relatively easily checked for information.
•
Hazcards; using the card names.
•
The index to Hazcards (pink cards); it does not matter if you only have the traditional name of a
chemical, other names are given and in most cases, this will lead to the correct card. Where the
substance is generally considered unsuitable for school use, the name is printed in bold.
•
The CLEAPSS electronic document E223 Chemical Stocklist and section 1.3 of the Handbook
(Chemicals: Hazard and Storage Data) which gives alternative names, storage class and hazard(s)
for each chemical.
•
A safety data sheet or material safety data sheet (SDS or MSDS) is now sent with every chemical;
the hazard along with risk phrases must conform to that provided by the Health & Safety Executive.
For chemicals that are not listed in HSE publications, the supplier is under an obligation to send
you their interpretation of the data. Note though, this can vary between suppliers.
•
The label for warning signs, or, if the bottle is old, a supplier’s catalogue which will give the main
warnings (if there is no warning on a recently-supplied bottle, the chemical can be assumed to
present minimal hazard in normal use).
•
The CLEAPSS Helpline for chemicals not listed in any of the above.
Beware of hearsay
Some exaggerated or untrue information does circulate. For example, some people quite confidently
state that ninhydrin is a carcinogen but, although it is both harmful and often in an unpleasant-smelling
solvent and so normally handled in a fume cupboard, there is no evidence of carcinogenicity. If there is
a worrying rumour, CLEAPSS is always ready to answer questions by letter, telephone, fax, email or
via our web site.
Few chemicals are banned but your employer has the final say
Despite rumours to the contrary, very few chemicals are actually ‘banned’ by law on a national basis.
The Department for Children, Schools and Families and the Association for Science Education have
published recommendations that certain chemicals are unsuitable for general use in schools and these
chemicals are printed in bold in the pink index to the Hazcards. Even these chemicals might still be
used after a Special Risk Assessment has been made. Some education employers have incorporated,
and sometimes extended, these published restrictions into their local rules. Legally, it is such rules
made by the employer (see section 2.1, The law and safety) that are important and they must be
heeded. However, if such bans exist, it is the employer’s responsibility to ensure staff know about them,
eg, by providing suitable training.
1
www.ase.org.uk/htm/teacher_zone/safety_in_science_education.php.
© CLEAPSS 2009
7.2
Section 7 - Page 3
Chemicals
Chemical names
This is a complex subject and only a few tips can be given here; further information is available in the
ASE publication Signs, Symbols and Systematics 16-191.
There are at least three types of chemical name.
Archaic or trivial
names
For example: sulfate2 of potash [for potassium sulfate(VI)]; green vitriol [for iron(II)
sulfate(VI)]; caustic soda (for sodium hydroxide).
These should have almost died out now, except in domestic and industrial use (usually as
slang), and are unlikely to be met in school science.
Traditional names
For example: potassium sulfate; ferrous sulfate; sodium hydroxide; sodium acetate; aniline.
These are sometimes used in commerce and old text books. They also appear in suppliers’
catalogues when the IUPAC3 name is too long and on bottles of old stock.
ASE-recommended
names based upon
IUPAC
For example: potassium sulfate(VI); iron(II) sulfate(VI); sodium hydroxide; sodium
ethanoate (or acetate); phenylamine. These, more consistent, names are now used widely
in teaching and by chemical suppliers
The more common ASE-recommended names and their alternatives are listed in The
CLEAPSS electronic document E223 Chemical Stocklist and section 1.3 of the Handbook
(Chemicals: Hazard and Storage Data). They can become very long-winded and suppliers
then go back to traditional or even trivial names. So 2-hydroxypropane-1,2,3-tricarboxylic
acid is still found as citric acid
Organic and inorganic chemicals
Grouping chemicals into these tradition categories goes back to the 19th Century and is considered by
modern chemists to be out of date. However, for storage purposes it is a very useful concept.
Organic chemicals (eg, ethanol, methyl benzoate, propanone) were originally thought to be of biological
origin, hence the term. However, organic compounds can be both synthetic and natural. A common
feature of them chemicals is that they contain chains of carbon atoms bonded to each other and to
hydrogen; other non-metallic elements (eg, oxygen, nitrogen, chlorine, bromine and sulfur) can also be
included in the molecule. A property of organic compounds (which links with storage) is that the
majority of organic compounds are combustible.
Inorganic compounds are the compounds of all the other elements and, somewhat confusingly,
includes elemental carbon, carbon dioxide, carbon monoxide, carbonates, cyanides, cyanates and
thiocyanates. These chemicals were thought to be of mineral origin and found in rocks. The majority of
oxidising agents4 found in schools are inorganic compounds except di(dodecanoyl) peroxide (see
Hazcard 29).
When it comes to labelling chemicals as organic or inorganic there are many chemicals that appear to
straddle the two, eg, the salts of organic acids and organometallics (rarely used in school chemistry).
However, the distinction remains useful.
1
Signs, Symbols and Systematics 16-19, Association for Science Education, 2000, ISBN 9780863573125. Signs,
Symbols & Systematics (5-16 Science), Association for Science Education, 2000, ISBN0863573126.
2
The spelling of sulphur etc recommended by the British Standards Institution (based upon IUPAC rules) is with an ‘f’
not a ‘ph’. There is, apparently, no etymological reason for using a ph and the f is considered more logical. This
spelling is now accepted by QCA but not penalised in exams. IUPAC did not accept the American version of
‘aluminium’.
3
International Union of Pure and Applied Chemistry.
4
They carry the risk phrase R8: Contact with combustible material may cause fire.
Chemicals
Section 7 - Page 4
© CLEAPSS 2009
Chemical names and chemical formulae
With a good background in chemistry, technicians and teachers could communicate with each other
using the chemical formulae. However, mixing chemical names and formulae in communications can
lead to mistakes and confusion. For example, sodium nitrate(III) (used to make azo dyes) has the
formula NaNO2 and sodium nitrate(V) (useless in the making of azo dyes), has the formula NaNO3. It is
quite easy to focus on the words ‘sodium nitrate’ and pick up a bottle of NaNO3. To avoid this possibility
it’s best to avoid using formulae in communications but to stick with the proper chemical name.
7.3
Storage of chemicals
For ease of use, section 7.3 is organised into the following sequence of subsections.
7.3 a
Arranging the chemicals by storage category.
7.3 b
Planning the store.
7.3 c
Chemicals with particular storage requirements.
7.3 d
Chemicals requiring periodic checks.
7.3 e
Stock control.
7.3 f
Improving the present store (the bottom shelf, types of shelving, security, signs).
7.3 g
Ventilation in chemical stores.
7.3 h
Designing a new chemical store.
In addition, there are two relevant appendices at the end of section 7.
Appendix 7A
Legal issues with regard to cupboards, ventilation, electrical fittings and materials
for building stores to hold more than 50 L of flammable liquids.
Appendix 7B
Model risk assessment for chemical storage.
7.3 a
Arranging the chemicals by storage category
Chemical storage must be safe and secure and the storage arranged so that individual chemicals can
be easily found and returned. The storage categories, along with an abbreviated code, for chemicals
used in school science are given in Table 7.1. These categories are given on the Hazcards for the
most common chemicals, in E233 Chemicals stocklist (on the Secondary Resource part of the web
site and the Science Publications CD-ROM) and section 1 of this Handbook, for any others.
Many chemicals have properties that correspond to more than one storage category. For these, the
best storage category is the one that has the highest priority in Table 7.1. For example, ethanoyl
chloride is both a CORROSIVE and HIGHLY FLAMMABLE chemical. For storage purposes though,
ethanoyl chloride needs to be stored in the flammables cupboard not with the corrosives.
© CLEAPSS 2009
Table 7.1
Section 7 - Page 5
Chemical storage categories and priorities for the chemical store
Priority
CLEAPSS Storage categories
Storage Code
1
Make when needed (do not store)
Situ
2
Special cases
Spec
3
Radioactives
Rad
4
Gas cylinders
Cyl
5
Flammable Liquids
FL
6
Flammable Water-reactive chemicals
FW
7
Flammable Solids
FS
8
Corrosive Liquids, acids
CLa
9
Corrosive Liquids, non-acids
CLb
10
Corrosive Water-reactive chemicals
CW
11
Corrosive Solids
CS
12
Refrigerator
Cold
13
Toxic chemicals
T
14
Oxidising agents
Ox
15
General chemicals (Inorganic)
GIn
16
General chemicals (Organic)
GOrg
7.3 b
Chemicals
Planning the store
Chemicals should be stored systematically. The arrangement you chose will depend on the amount of
space you have available. For any concerns about the safety of your arrangement, contact CLEAPSS
on the Helpline. There is no requirement for a discrete secure cupboard for storing toxic chemicals as
long as the store itself is secure. However, there are legal requirements that require safe and secure
storage for flammables. There must be no flammable chemicals within the vicinity of gas cylinders or
radioactive chemicals.
When planning, or re-planning, chemical storage we have found it useful to draw out a schematic plan
of the arrangement of storage categories within the store (similar to Figure 1a, 1b or 2). It is then quite
easy to identify any potential, or actual, weaknesses and how arrangements might be altered to
overcome them.
Figures 1a and 1b illustrate possible arrangements in a dedicated chemical store. The presence of a
flammables cupboard means gas cylinders and radioactive material must not be stored here. Both
examples provide an area for the flammables cupboard, the refrigerator and the corrosive acids and
alkalis. In Figure 1a, the technician has decided to separate the organic chemicals from the inorganics.
This means the many inorganic oxidising agents can be stored with the General Inorganic chemicals
(GIn). In Figure 1b, both inorganic and organic chemicals have been combined which means a
separate area / cupboard is required for all oxidising chemicals to maintain separation from combustible
organic chemicals.
Chemicals
Section 7 - Page 6
CW
FW
Spec
© CLEAPSS 2009
CW
FW
Spec
FW
FW
Rad
Rad
GIn
CS
T
FS
Ox
GIn
Situ
GOrg
T
GOrg
T
CS
FS
Ox
T
Cyl
Cyl
o
<5 C
o
<5 C
CLa
CLa
CLb
<50 l
Situ
CLb
<50 l
Cold
FL
Inside the store
Cold
FL
Inside the store
Outside
Outside
the store
Separating the organic and inorganic chemicals,
but both in alphabetical order.
the store
Combining the organic and inorganic chemicals,
all in alphabetical order.
Figure 1a
Figure 1b
Figure 2 shows a possible arrangement for a school that has an outside and an internal store.
CW
Spec
FW
FW
Situ
Ox
GIn
GOrg
T
T
CS
FS
CS
FS
Rad
<50 l
Cyl
o
<5 C
CLa
CLb
Cold
FL
A possible arrangement when there is an external store. If there are no gas cylinders, the radioactive
cupboard could be placed in the internal store.
Figure 2
There are many other arrangements that are possible. Much will depend on the size and situation of
the store within the science suite.
© CLEAPSS 2009
7.3 c
Section 7 - Page 7
Chemicals
The particular requirements of each storage category
This section looks at the requirements for each category in the order given in Table 7.1.
Make when
needed [Situ]
Situ
Special Cases
[Spec]
These chemicals or preparations should be made when needed and disposed of
immediately afterwards. They should never be found in the store cupboard at
all. Some such chemicals are unstable. For example, Tollen’s reagent, ammoniacal
silver nitrate(V) solution, has been known to explode when stored for long periods
of time; Chlorine water does not keep because the gas leaks into the atmosphere
affecting lungs and corroding metal. Both should be prepared just before use and
disposed of directly afterwards.
Bromine: (Hazcard 15A) bromine fumes, leaking from the container, affect lungs
and accelerate the corrosion of metal cupboards and any other metal objects in the
store. Keep liquid bromine bottle inside a closed container with soda lime present,
which should be renewed regularly. This can be stored on shelves in a secure
store. Purchase small quantities (100 cm3 or less). Open this container in a working
fume cupboard. Check condition of the caps regularly; they have been known to
split. A bottle contain about 500 cm3 of 1 M sodium thiosulfate should be kept next
to the bromine so that any spills on the skin can be washed off immediately.
Hydrated sodium carbonate (washing soda) should also be kept close by to be
poured onto a spill of liquid bromine onto any surface.
Keep ampoules in their protective packing with other corrosives. Take only the
required number of ampoules into a class.
Prompt action is essential in the case of a bromine spill or evacuation will be
unavoidable, so suitable neutralisers must be kept with it at all times.
Spec
Silicon(IV) chloride: (Hazcard 86) Silicon(IV) chloride is a liquid that reacts with
water (hydrolysis) to form hydrogen chloride gas and solid silicon dioxide. Once
opened, any silicon dioxide formed around the mouth of the bottle seals it. Sealed
bottles of silicon(IV) chloride have been known to explode during hot weather. Store
bottles of silicon(IV) chloride inside another container which contains silica gel
desiccant. Monitor the bottle regularly to check that the top can be opened. Keep
small quantities only (100 cm3 or less). Dispose of any remaining after 2 years.
(Ampoules keep indefinitely.) It is advisable to prepare silicon(IV) chloride in situ,
see CLEAPSS guidance leaflet PS 84, Making and using silicon(VI) chloride.
White phosphorus: (Hazcard 73A) White phosphorus is best stored with the toxic
chemicals. The solid must be kept under water. Change the water frequently by
flushing through with fresh water from the tap. Keep away from sodium, potassium
and oxidising agents. The addition of sodium chloride to the water will reduce the
risk of the bottle breaking caused by the water freezing. Never store white
phosphorus in an outside store because if the water freezes, it may crack the bottle.
White phosphorus is not currently available from suppliers because of importing
problems.
Rubidium chloride: (Hazcard 47B) The naturally occurring isotope 87Rb (which
forms 27.8% of all rubidium) is radioactive. However, the energy released is low
and, with the amounts used in schools, the Ionising Regulations 1999 do not apply.
If kept as a radioactive substance, store in the radioactives cupboard but, if kept for
flame tests, keep with General Inorganic chemicals [GIn].
Chemicals
Section 7 - Page 8
© CLEAPSS 2009
Radioactives
[RAD]
These should be kept in a metal container, which is locked away, not in the room
where flammables are stored, and at least 2 m from any position where one person
habitually works. See Guide L93, Managing Ionising Radiations and Radioactive
Substances, Hazcards 101 & 105.
Gas cylinders
[Cyl]
If schools have only one cylinder of each gas, they do not need to be ‘stored’. They
are ‘ready for use’ and can be kept in the prep room in a suitable clamp or trolley.
They must not be kept in the same room as the flammables storage. A sign should
be placed on the door where the cylinders are kept. Oxygen and hydrogen cylinders
can be kept next to each other, provided there is no possibility of the chemicals
reacting together. See Handbook 9.9 for a general discussion on gas cylinders. For
information on a specific gas also see the relevant Hazcard.
Extremely &
Highly
Flammable
Liquids [FL]
If the total volume of these chemicals is less than 50 L, they can be kept in a fireresistant cupboard in the chemical store or prep room. Ventilation of the store is
required but not of the cupboard. Schools should avoid holding larger quantities
than 50 L but if it is necessary to store larger quantities it will need to be in a fireresisting store, possibly outside. This storage category applies to all extremely and
highly flammable liquids and some flammable liquids with a flash point of less than
32 °C.
(See appendix
7A for legal
issues)
<50 l
FL
Flammable
WaterReactives
[FW]
FW
These chemicals, such as sodium and calcium carbide, are best kept in a special
boxes or cupboards, and should be kept away from water and water-based
reagents. They should not be stored with flammable liquids or in the flammables
cupboard. Alternatively, it is cheaper and nearly as effective to keep these metals in
the containers in which they are supplied. These give good protection against
breakage of the bottle inside.
A simple box for flammable water reactive metals could be made of wood with a
lining of the material used in heat-proof mats. It is important that such boxes should
be constructed so that bottles cannot overturn inside. This may be achieved by
using dividers made of the fire-proof board. The figure shows the design used at the
CLEAPSS which will take four larger bottles and three smaller ones. This should be
large enough for all schools. The box can be placed on a shelf in the secure
chemical store or in a locked cupboard in the prep room or laboratory.
FW
!
Flammable
Solids [FS]
Chemicals, which have the risk phrase R10: Flammable, do not need to have a
hazard-warning symbol on the bottle. The phrase applies to liquids with flash points
between 21 and 55 °C. If you can keep all chemicals with flash points below 55 °C
in the flammable store and the total volume is less than 50 L, then do so. If you
have just more than 50 litres, those chemicals with flash points above 32 °C could
be placed on the GOrg shelves.
Check that potassium and sodium bottles are returned to the prep room or
store immediately after use. There have been several instances of them being
stolen by pupils. Only dispense the quantity required and check with the
teacher how much was actually used.
These chemicals, such as sulfur, red phosphorus and ammonium dichromate(VI),
should not be stored with flammable liquids or oxidising agents. They can be kept
on shelves in a secure store with GIn, or in secure cupboards but they should not
be kept next to any chemicals from the Ox group.
© CLEAPSS 2009
Corrosive
Liquids, Acids
[CLa]
CLa
Corrosive
Liquids,
Non-Acids1
[CLb]
CLb
Corrosive
WaterReactives
[CW]
Section 7 - Page 9
Chemicals
These chemicals, such as concentrated hydrochloric acid, should be kept in a
ventilated cupboard or, in a chemical store, low down at floor level. They should be
protected from being kicked over, for example by standing the bottles on a layer of
breeze blocks, behind a wooden bar or inside large plant troughs. Ventilation of the
room is essential. There is no legal requirement for corrosive cupboards. There
should also be containment of the liquid to avoid corrosive acids dripping onto the
floor. Cat litter or sand can be used.
These chemicals, such as 880 ammonia, should be kept in a similar way to group
CLa but as far from that group in distance as possible, e.g. separate ventilated
cupboards (a very expensive option!) or opposite ends of a bottom shelf in a
ventilated storeroom. Ventilation of the room is essential. They should be protected
from being kicked over - for example, by standing the bottles on a layer of breeze
blocks, behind a wooden bar or inside large plant troughs. There is no legal
requirement for corrosive cupboards. There should also be containment of the liquid
to avoid corrosive acids dripping onto the floor. Cat litter or sand can be used.
These awkward fuming chemicals, such as anhydrous aluminium chloride, should
be in a special ventilated cupboard but these are not easily available in schools. It is
possible to absorb the fumes by placing the bottle in a container with soda lime. The
tops of these bottles should be regularly checked. These could also be kept with
CLa.
CW
Corrosive
Solids [CS]
These chemicals, such as sodium hydroxide pellets, can normally be stored with
general chemicals, either inorganic (GIn) or organic (GOrg).
Materials kept
in a refrigerator
[Cold]
These materials degrade or have shorter shelf lives at room temperature and
should be kept at temperatures below 5 °C. This covers all enzymes, including
powdered enzymes, see Hazcard 33. It is advisable not to store highly flammable
liquids in a domestic fridge2.
Very Toxic and
Toxic
Chemicals
[T]
These chemicals, such as mercury and lead salts, can be stored with the general
chemicals, GIn or GOrg, if these are sufficiently secure. A locked cupboard is
advisable if they are stored in the prep rooms or a laboratory. There is no reason to
have a separate ‘Toxics’ cupboard in a locked chemical store.
1
Chemicals in both these groups are labelled CORROSIVE, with the same symbol. It is easy to identify the acids from
their name and the others, which are likely to be alkalis, should be put in the second group. The need for this
segregation is illustrated by the example of sodium chlorate(I) (hypochlorite) which releases chlorine with acids.
2
It is required to cool ethanol when extracting DNA so using the fridge with a minimal amount of ethanol (flash point is
13 °C) is possible.
Chemicals
Section 7 - Page 10
Oxidising
Agent
[Ox]
© CLEAPSS 2009
These chemicals, such as potassium chlorate(V), can be stored
with general inorganic chemicals (GIn). They should not be stored
with organic chemicals (GOrg) which are combustible. The only
organic oxidising agent schools may have is di(dodeanoyl)
peroxide (Hazcard 29), which should not be stored with the
organic compounds but separated by space or placed inside
another container.
Ox
General
Chemicals
[Gin] & [GOrg]
A small cabinet can be used If separation from other combustible
organic compounds is required.
It is usual to divide remaining chemicals into inorganic and organic groups whether
harmful, irritant or neither, and this should be done in order that oxidising agents
may be separated from the organic chemicals. Ideally, all chemicals should be
under lock and key but, if storage is difficult, only those with no hazard warning
should be on open shelves in the prep room.
Note that CLEAPSS also advises against storing chemicals, or made up solutions,
in jam jars, plastic drink bottles, etc, whether in the prep room or chemical store.
7.3 d
Chemicals requiring periodic checks
This group of chemicals include those which may build up pressure in their bottle, and others which are
linked with very specific problems. Comments are given in Tables 7.2 and 7.3 respectively.
Table 7.2
Chemicals that may build up pressure in the bottle
Problem
Chemicals that
decompose.
Chemicals that
react with water
to generate a
gas.
Gases which are
dissolved in
water.
Chemicals with
low boiling points.
Comments
These decompose slowly to form a gas so that, in an
unvented bottle, the pressure rises gradually. Then,
when the bottle is opened and pressure suddenly
released, the gas may come out of solution throughout
the volume of the liquid so that, in extreme cases, it
appears to boil and froth out of the top.
Water reactive chemicals react with water or water
vapour in the air. Pressure tends to rise unpredictably
after the bottle has been opened and re-closed. Look
for white deposits2 appearing around the cap of the
bottle. Care should be taken when handling these
chemicals that water or excessive amounts of water
vapour do not enter the bottle. Never return unused
chemicals of this group to their bottles.
In hot weather, the pressure in the bottle rises. They
should be stored in as cool a place as possible. Always
loosen caps carefully; particularly in hot weather, it is
sensible to open bottles in a working fume cupboard.
Look for white deposits2 appearing on the bottles.
Chemicals with low boiling points evaporate sufficiently
at room temperatures to cause the pressure to build up
in the bottle. They should always be stored in cool
conditions and, if the flammable-liquid storage is not
always cool, consideration should be given to moving
such liquids.
Examples
Sodium chlorate(I)
(hypochlorite) solution,
100 vol hydrogen peroxide,
fuming nitric acid1.
Aluminium chloride,
phosphorus chlorides,
ethanoyl chloride,
benzoyl chloride,
sebacoyl and adipoyl chloride,
silicon tetrachloride.
For silicon tetrachloride,
see the special entry below.
Concentrated ammonia,
concentrated hydrochloric
acid.
Ethanal,
ethoxyethane,
pentane.
1
A chemical that schools should not have. It needs to be removed by an authorised water contractor.
2
Usually ammonium chloride which is also a sure sign of poor ventilation.
© CLEAPSS 2009
Table 7.3
Section 7 - Page 11
Chemicals
Specific chemicals which require special attention
Bromine:
check the cap
The caps which are fitted to bromine needs to be regularly checked for splits. It
might be possible to ask your supplier via their rep for a spare. A distinct odour and
corrosion of any nearby steel is a sign of split cap.
Bromine should be stored with hydrated sodium carbonate and approximately 1 M
(20% w/v) sodium thiosulfate solution. These neutralisers should be kept with the
bromine at all times, when it is being transported from the store and when it is being
used, in case of spills. A beaker, bowl or bucket, large enough to immerse, for
example, a hand or arm, should also be available and the volume of thiosulfate
solution should be sufficient to cover the affected part of the body. See Hazcard 15A
for details. However, if spilt in the open, anybody dealing with the spill may be
putting themselves at risk. If possible, open the windows then seal off the room and
contact CLEAPSS immediately. You must not put yourself at risk.
Ethers:
checking for
peroxides
Ethoxyethane (diethyl ether), any other ethers and cyclohexene, if stocked, should
be checked regularly for peroxides. If bottles are stored in the dark, a yearly check is
enough but, if kept in the light (even in a brown bottle), the ether should be checked
every term. Details for testing and removing peroxides are found on Hazcard 42. In
the past, technicians have reported a positive peroxide test for newly acquired
ethers and cyclohexene. The presence of peroxides is only a worry if the chemical is
boiled to dryness - not an issue with most school chemistry.
Mercury take care to
avoid spills
Mercury needs to be stored particularly carefully as it causes problems if spilt. See
section 12 of the Handbook for full advice on handling mercury. It is important to
note that mercury should always be stored in a robust bottle (large plastic bottles
more than a third full have been known to burst at the seams) and the bottle(s)
should stand in a tray. A mercury spills kit should be available (see section later,
section 7.7).
White
Phosphorus check water
levels regularly
Phosphorus (the white variety) has already been singled out as a special case as it
is difficult to decide where to store it. It should be checked regularly (at least every
term) to ensure that the water is well above the solid. So that this may be done
easily, it is best to keep it in a clear bottle. The water should be replaced every year;
this should be done by flushing rather than by emptying and refilling. Phosphorus
should never be in an unheated outside store; freezing may break the bottle, with
the phosphorus exposed after a thaw. This may also occur in an internal store;
adding 1-2 spatula measures of salt to the bottle minimises the risk.
Potassium check for
yellowing
Stocks of potassium should be checked regularly for signs of yellowing. If this
occurs, it should be destroyed. See Hazcard 76.
Sulfur dioxide check the valve
Sulfur dioxide canisters are now unobtainable. Any remaining in schools should be
checked every term to see that valves are working freely and not corroded.
Remember that valves should only be finger tight. If a valve becomes stuck, it is safe
to empty the canister by removing the valve in an efficient fume cupboard. If this
does not work then contact CLEAPSS.
Silicon
tetrachloride keep dry
Silicon tetrachloride has already been singled out; it is clearly a CORROSIVE waterreactive liquid but a particularly hazardous example since many cases of bottles
exploding violently have been reported. It is essential to take all possible precautions
against water entering. It should never be returned to the bottle and it would not be
too extreme to avoid its use on very wet days. When a bottle is to be opened, it
should be covered with a thick cloth and placed in a fume cupboard before the cap
is cautiously unscrewed. Face shield, gloves and a lab coat should be worn. Before
replacing the cap after use, wipe the outlet with a tissue. If the smallest stock
obtainable is not used within two years, it should be destroyed.
Chemicals
7.3 e
Section 7 - Page 12
© CLEAPSS 2009
Stock control
Chemicals as
gifts
Do not accept chemicals as gifts unless you are really sure you want them. Those
giving you the chemical may be trying to avoid hazardous-waste collection charges.
Delivery
CLEAPSS has been told of chemicals delivered upside down, badly packed, leaking
(into the Head Teacher’s office), thrown onto a trolley by caretakers or left
unattended in a place where children congregate. Surprisingly, there is no
requirement to put a “this way up” notice on a package, although this may change
with future EU Regulations. Any sign of leaks and smells from packages need to
taken up with the supplier immediately (and inform CLEAPSS as well). The rules
behind chemical packaging are extremely complex. Supply companies are well
aware of their obligations in this matter and take the regulations very seriously. A
written risk assessment should be produced to as a set of guidelines to cover what
happens when the school receives a delivery of chemicals. Particular attention
should be paid to the 3.30 pm Friday afternoon delivery and that the chemical may
will remain in the reception area over the weekend. Examples of effective
procedures could include that the science department must be informed of a
delivery of chemicals immediately, or that only the science technician should sign
for the package and move the packages away from the reception area where
children and parents may mingle.
On receipt of
the chemicals
in the store
Do check that the order is correct; occasionally the wrong chemical is delivered.
The current date should be written on the bottle.
Checking stock
There is no requirement to check stock in and out of the store every time a chemical
is used. Once a year, an inventory of the chemical stock should be taken. This is a
two-person job, one to do the examination of bottles and the other writing or typing
the results. E233 Chemical stocklist (on the Science Resource part of the
CLEAPSS web site and the CD ROM) is designed to assist technicians in this task.
A useful stock control tip is, if you can see the level of the chemical in the bottle,
mark the level with a permanent marker. If this chemical is not used after several
years, then consideration should be given to having it removed by an authorised
contractor (see Guidance leaflet PS5 Waste Disposal Contractors). The expiry date
on a chemical is not relevant to schools. It is there to warn users that, after that
date, the assay of the chemical cannot be relied upon.
Record keeping
The records should be kept in the store, the prep room and in an office not in the
same building as the science department. If the laboratories are destroyed by fire, a
record of the chemical store can be obtained quickly for insurance purposes.
“A COSHH
assessment”
A correct term should be a risk assessment for the chemicals in the store. Appendix
7.b has a model risk assessment which you can adapt to the situation in your
school. You will find a word version in Customisable Documents on the Science
Resource part of the CLEAPSS web site and the CD ROM.
© CLEAPSS 2009
7.3 f
Section 7 - Page 13
Chemicals
Improving the present store
Having the opportunity to design a store for a new building is rare but a risk assessment may show that
some improvements to an existing store are necessary. The list below includes common aspects of
concern and each is described in more detail after the list.
•
The bottom shelf.
•
Shelving.
•
Security.
•
Warning signs.
The bottom shelf
In the chemical store, the bottom shelf is reserved for large bottles (except those that go in the
flammable cupboard) and corrosive liquids. These bottles are placed low down so there is no change of
the chemical spilling over the person collecting the bottle. Chemicals have been known to spill over
people when removing bottles containing liquids from shelves above shoulder height. However, bottles
at floor level can be at risk of being accidentally kicked.
To protect bottles from being kicked, a platform or plinth (150 mm to 300 mm deep) can be arranged
(see Figure 6). A raised shelf or plinth can be:
•
a raised concrete level,
•
concrete blocks, as sold for building work or garden paving,
•
a wood block(s) which can also be covered or sealed as for shelves.
To make provision for containment of the liquid if an accident occurs, surround the plinth by a sill
spaced about 100 mm away, filling the space with inert absorbent, such as cat litter, sand or expanded
mica (Vermiculite). If an accident should occur, the wet absorbent can be scooped up into a bucket and
dealt with. Figure 3 shows the arrangement.
Bottle in use
Reserve bottle
Mineral absorbent
(Cat litter)
Raised shelf
100 mm
300 mm
100 mm
Figure 3
Containment of a spill can also be achieved surrounding the bottles with a ‘bund’: a wall of brick or
breeze block, typically 15 cm high. If there are only a few bottles, they can be placed in plastic
containers which have enough volume to contain a catastrophic spill from 1 bottle. It would be unwise
to lift all these bottles in one tray though.
Chemicals
Section 7 - Page 14
© CLEAPSS 2009
Both expanded polystyrene bottle packs, used by chemical firms for transporting liquids, and Safepaks,
a type of outer plastics container used by some chemical suppliers for the supply of corrosive liquids
and water-reactive corrosive chemicals, are useful.
Wooden shelving
A set of wooden shelves with the suggested dimensions provided in Figure 4, is a useful way to
organise the store. The top shelf for storing chemicals should be no higher than 1.6 m from the ground
although higher shelves might be used for little-used apparatus, etc. Estimates of the shelf lengths
needed for the various categories are given in section 20.5 of the Handbook.
150 mm
250 mm
Overall
height
1.51 m
150 mm
250 mm
150 mm
250 mm
150 mm
380 mm
300 mm
380 mm
Mineral absorbent
300 mm
Large shelf:
large bottles of solids
Bottom shelf:
large bottles of liquids
Figure 4
Corrosion occurs on any metal brackets used to hold shelving up. With aluminium brackets, low
concentrations of hydrogen chloride fumes over several years can give rise to aluminium chloride dust.
For steel brackets, the finish should be of good quality so that rusting is kept to a minimum. If corrosion
goes too far, then the shelf supports can give way, which is why ventilation is so important.
The problem with a wooden shelf is that the surface absorbs any spilled chemicals. The surface could
be sealed with a rub-in-wax polish, varnish or it could be covered with hardboard or plastic trays. White
–faced chipboard is better than wood as spillages are easy to wipe away. Plastic flowerpot holders from
garden centres could also be used to stop drips from the bottle affecting the shelf surface.
© CLEAPSS 2009
Section 7 - Page 15
Chemicals
Lips on shelves
Lips on shelves are a contentious issue: some employers prefer shelves to have
them. However, bottles may be knocked against the lips as they are removed from
the shelf. There is no evidence of bottles committing suicide by throwing
themselves off the ledge of the shelf. Consequently, there seems no real need to fit
them.
Racking
Racks can be obtained from commercial
or educational shelving suppliers. Extra
shelves can be obtained. The runners /
supports are metal and the shelves are
chipboard, which should be protected
with trays or hardboard. The metal is
painted but needs to be inspected for
signs of corrosion. They are rather deep
shelves so bottles will be placed behind
others. Trays could be used to aid the
division of bottles on the shelf.
Sliding draw
storage
Many schools store equipment in
storage systems that use plastic trays
that will fit into racks in storage units or
trolleys. They are not really suitable for
the storage of the general chemicals. If
the trays become to heavy, they slip
from the runners and because the
bottles are packed together, the labels
are hidden from view. It takes time to
locate the chemical. However, the trays
are suitable for storing small bottles of
the same type of chemical such as
indicators.
Rolling
systems
Some commercial shelving systems are mounted on wheels running on a track,
allowing many shelving units to be packed into a small area with only one gangway
space. Surprisingly, such systems are acceptable for chemical storage; their inertia
is large so lurching leading to bottles being spilled does not occur. Care has to be
taken, of course, that bottles are never left on the floor and crushed between
shelves.
Arranging of
chemicals on
shelves
The ideal situation is that there is enough space to place the bottles next to each
other. However, space is always at a premium in a storeroom and it will be almost
impossible to have a separate space on a shelf for each chemical. It will be
necessary in this case to place infrequently-used chemicals behind other chemicals.
An up to date stocklist is very important.
Chemicals
Section 7 - Page 16
© CLEAPSS 2009
Security
!All hazardous chemicals and preparations, no matter where they are stored, should be made
secure so that no student or casual visitor can easily remove them.
CLEAPSS has received calls from schools where chemicals have gone missing from the prep room.
This has even occurred during open evenings. It is important that the door(s) to the chemical stores
and any cupboards that house the chemicals are kept locked. If there is a single chemical store with
secure access, there is no requirement to lock cupboards inside although is would act as another level
of security. If chemicals are stored in laboratories, the rooms must be kept locked when not in use and
no child must be present without a teacher there as well.
Warning signs
Signs on the doors of rooms or buildings where chemicals are stored are usually for the benefit of fire
fighters but also warn others (eg, workers) not familiar with the site. However, schools may,
understandably, be reluctant to identify chemical stores to intruders since this may encourage them to
make more mess or damage than they otherwise would.
The Health and Safety (Safety Signs and Signals) Regulations (see section 8.6 of the Handbook)
require that “areas, rooms or enclosures used for the storage of significant quantities of dangerous
substances or preparations must be indicated by a suitable warning sign”. The interpretation of the
word ‘significant’ and ‘suitable’ may depend on the local safety officer and fire-prevention officer (if
consulted). Unless stated otherwise the danger warning (Figure 5a) should go on the door of the prep
room and/or chemical store. The highly flammable sign (Figure 5b) should go on the flammable cabinet
(if you have a cabinet for corrosives, the corrosives warning sign can go on that.) Wherever the gas
cylinders are kept, the gas cylinder warning sign (Figure 5c) can go on the door.
Figure 5a
Figure 5b
Figure 5c
Printable versions of these signs can by found in the electronic document E232 Common Safety Signs
& Hazard Symbols which is in Secondary Resource on the webs site and on the Science Publications
CD-ROM.
Where an educational establishment has so large a quantity of highly-flammable liquids that a separate
store (either internal or external) is required, then this store would probably be regarded as holding a
significant quantity and it must have a warning sign to comply with the above Regulations.
For details of warning signs needed for the storage of radioactive materials, consult the guide L93,
Managing Ionizing Radiation And Radioactive Substances.
© CLEAPSS 2009
7.3 g
Section 7 - Page 17
Chemicals
Ventilation in chemical stores
Chemical stores are legally required to have adequate ventilation (For more details see Appendix 7A).
CLEAPSS hears of storerooms and prep rooms with no ventilation at all, or at best a single opening
window, which is not acceptable. Poor ventilation where chemicals are stored gives rise to:
•
odours, usually coming from the flammable cupboard,
•
a white powder (ammonium chloride) over bottles where corrosives are stored and sometimes in
the flammable cupboard,
•
a very thin liquid film over bottles,
•
corrosion of metal surfaces, eg, white powder on aluminium and rust on iron and steel surfaces,
•
complaints of headaches and tiredness.
As far as is possible, fumes from chemicals should be dealt with at the point of release by ensuring
containers, lids, etc. are properly closed. Make sure that the screw-top lids and tops of bottles are
cleaned before being put back together. Also, make sure that those bottles which give rise to the worst
fumes are kept in outer containers with a suitable absorbent between the bottle and the container.
Ventilation of chemical storage areas can be provided by the following:
A fume cupboard
Fume Cupboards in Schools, Building Bulletin 88 recommends that a fume cupboard should be sited in
newly-built prep rooms. Although the fume cupboard itself should not be used as a storage area for
‘nasties’ such as bromine, the cupboard underneath can be connected to the flue and the corrosives
placed there. Even if the fume cupboard is not working, any fumes will vent out of the storage cupboard
by natural ventilation.
A fume cupboard 1 m wide, open at 400 mm and running 0.45 m sec-1 would extract 1 x 0.4 x 0.45 x 60
x 60 or 648 m3 of air per hour. To work out the air changes per hour, the volume of the room is
required. If the volume of the room is 250 m3, then the extraction rate is 2.6 ach. Unless the room is
very small, this is not enough ventilation for a working prep room, which should have at least 5 ach.
Mechanical ventilation
Two good examples of mechanical ventilation in a school chemical store are shown in the photographs
below. Note how large the openings to the ventilation vents have to be have to be to achieve an
appropriate flow rate.
Ventilation rates should be checked regularly. The best method is to use the anemometer used for
fume cupboard measurement. Place it against the grill and note the speed. The dimensions of the open
area of the fan should be measured and the area calculated. Vents will become covered by dust and
cobwebs, and should be cleaned regularly to maintain a good air flow.
Chemicals
Section 7 - Page 18
© CLEAPSS 2009
The area of the opening in the fan in Figure 14 is found by measuring
the radius of the hub, r, and the circular opening, R (see Figure 6).
These need to be converted to metres.
The area is found by using the equation; Area = π ( R − r )
2
2
r
R
Figure 6
Air bricks
Air bricks have been thought adequate on their own for the ventilation of chemical stores. However,
they get covered, and even blocked by dirt, on the outside, shelves, cupboards and large containers on
the inside. They are often too small and there is only one when there should be at least 2 to ensure
circulation.
7.3 h
Planning a new chemical store
Where a new school is being built or, sometimes, older premises are being adapted or extended, then
design recommendations in Science Accommodation in Secondary Schools, BB80 (and complemented
by CLEAPSS Guide G14 Designing and Planning Laboratories) should be followed1. However, this
advice is not always taken up, through ignorance that the advice exists, financial constraint or
constraints from the design of the rest of the building. In any of these cases, it will be necessary to cope
with what facilities are available in the school. We frequently hear of good initial designs, which are
thought to be suitable, suddenly disappearing from final plans as finances become an increasing
constraint. Heads of Science and Senior Technicians should constantly monitor progress as building
proceeds.
The basic requirements of an effective chemical store have already been considered. This section is
mainly about where the store could be located.
Location options
The following 5 basic options listed below describe all the common possibilities and will come close to
the situation in your school. However, since school design varies greatly, careful individual planning
and organisation is required.
A separate internal chemical store
The best option is one, large internal windowless, ventilated, storeroom, with direct access to the prep
room through a lockable door. Figure 7 shows a typical design from Science Accommodation in
Secondary Schools, BB80. The walk-in chemical store is in the top left-hand corner. It allows the
storage of chemicals to be simple and straightforward. A flammable cupboard will be necessary but
other internal cupboards are not, and the store will be secure. Manual Handling issues are also
minimised.
1
Science Accommodation in Secondary Schools, BB80, DFES, 2004; a copy can be downloaded from
www.ase.org.uk/ldtl/documents.html.
© CLEAPSS 2009
Section 7 - Page 19
Chemicals
Figure 7
Using the prep room
The second option would be a large prep room with a section given over to chemical storage. There
must be a lockable flammable cupboard and lockable cupboards will be required for many of the other
categories of chemicals. Low hazard chemicals could be kept on the open shelves, but, in some
schools, it may even be prudent to put these into locked cupboards. All these cupboards place a great
strain on storage space in the prep room. However, in prep rooms designed to service biology or
physics departments with a limited number of chemicals, this may be the best option. Security is vital. It
is important that a prep room containing chemicals remains locked at all times when unoccupied by
(science) staff.
Using several small store rooms
Such storage rooms are often situated away from the main prep room (which can be quite small) either
off corridors or at the back of laboratories. Many science departments are designed in this way.
Chemicals can be distributed by their various storage categories but there will be security and extra
manual handling issues here. For instance, one or more teachers might like to work in one of these
rooms, using it as a small office and perhaps, on occasions leaving the door open if they are called
away for a moment. A technician may have to walk some distance carrying bulk corrosive liquids.
There has to be well considered arrangements for situations like this, with high levels of staff
agreement on working rules and adherence to them.
An external Store
External stores are generally intended to house most of the chemicals, with small samples of chemicals
kept in the prep room as required. An outside chemical store might be necessary for one or more of the
following reasons.
•
There may be no space inside the building to store chemicals.
•
The storage space inside the building may be inadequate to store all of the chemicals. This usually
applies to establishments with very large 6th forms.
•
The fire-prevention officer (if consulted) insists on an external store because of the volume of
flammable-liquids stocked.
Chemicals
Section 7 - Page 20
© CLEAPSS 2009
However, there are several arguments against the use of outside stores for schools.
•
Technicians will be called upon to carry bottles some distance in the rain and snow, through doors
(especially fire doors) and possibly up or down stairs.
•
It is likely that trolley access will be difficult because of steps, stairs and rough surfaces.
•
In hot weather, external stores often become very warm indeed and pressure builds up inside
bottles of volatile chemicals.
•
In cold weather, liquid chemicals and solutions will solidify. Aqueous solutions will expand on
freezing and cause glass bottles to break. There is a particular problem with storing white
phosphorus.
•
Vandalism and theft of chemicals from external stores has occurred.
•
It is particularly difficult to ventilate an external store adequately yet keep it secure.
•
Full external hazard labelling of stores advertises their contents.
•
Caches of chemicals tend to build up in the prep room on benches and fume cupboards because
taking the chemicals back is too much hassle.
•
It is quite common for such stores to become damp and mould grows. Labels fall off bottles.
Cardboard boxes become weak.
•
Outside stores become a depository for other materials used by grounds staff and caretakers; in
these conditions metal containers of petrol and oil have been known to rust and leak
•
External stores should be heated (eg, with a thermostat set to about 10 °C) to protect the building
from the effects of frost and condensation. The cost of this is one of the major arguments against
such stores
•
If the need for an outside store is because of large quantities of chemicals be aware that the DSEA
Regulations (Dangerous Substances and Explosive Atmospheres Regs) do not advise storing
highly flammable chemicals in bulk just because it is cheaper to buy them that way.
Some schools have spent several thousand pounds on siting and building clean, dry, temperaturecontrolled outside stores, which are very effective.
Securely-locked steel bins are available. To date, there has not been any clear evaluation of their use
in schools, although reports do indicate that rusting of any iron / steel occurs and the acidic atmosphere
affects the legibility of paper labels.
External stores should be placed as far as possible in the shade of the parent building to minimise solar
warming.
The fire-prevention officer (if consulted) may insist on an external store because of the volume of
flammable liquids stocked. A cheaper option is to reduce stocks of flammable liquids and order as and
when required.
(See Appendix 7B for further information on the building material for outside stores and internal
flammable stores for holding more than 50 L of flammable liquids.)
Using school laboratories
There may be so little room for storage in the prep rooms that chemicals have to be stored in the
laboratory. In this case, all cupboards must be locked after use. In very small schools such as PRUs
(Pupil Referral Units) some prep schools or middle schools, which have just, one laboratory, no prep
room and use a limited number of chemicals, this may be the only option. For these, there must be a
small, secure flammables cabinet, secure storage for corrosives and at least one other secure
cupboard for the other chemicals. If storage is even more limited, the school can purchase diluted acids
instead of preparing their own, thus doing away with the secure storage for corrosives. It may also be
possible to liase with the nearest secondary school whose technician could prepare small volumes of
required acids and alkalis.
© CLEAPSS 2009
7.4
Section 7 - Page 21
Chemicals
Handling and dispensing large volumes of chemicals
Dispensing chemicals can involve handling large volumes of hazardous liquids, sometimes in heavy or
awkwardly-shaped containers, with poor pouring characteristics. For example, liquid poured from a new
bottle with a narrow neck will splash from the bottle and pour unevenly. The risks to those involved,
usually technicians, are much greater than with the small volumes generally used in a laboratory. A
higher level of personal protection, as described below, may therefore be needed, and the risk
assessment must take this into account.
Fume cupboard
Use a fume cupboard when pouring a liquid that is highly flammable or toxic. Some acids and alkalis
may be labelled corrosive but they also emit toxic vapours, so it is better to dispense them in a fume
cupboard.
Eye protection
Wear goggles or preferably a face shield when dealing with bulk toxic, corrosive or highly flammable
liquids.
Gloves
Chemical resistant gloves can be used with any chemical and are ideal. Disposable nitrile gloves would
be suitable for toxic chemicals. However, be very careful about touching your skin with these gloves
because they might have a chemical on them.
Clothing
A laboratory coat will protect clothes from chemical splashes. Open-toed shoes are unsuitable.
Carrying corrosive liquids
2.5 litre bottles of acid or alkali should be held with two hands, one supporting the bottom of the bottle.
For journeys from one room to another, a bottle carrier should be used.
Most bottle carriers are not suitable for pouring; only types in which the lid is fixed firmly with the neck
of the bottle poking through a hole are suitable.
Some liquids have a specific gravity more than 1, eg, a 2.5 L bottle of concentrated sulfuric(VI) acid will
weigh in excess of 4.5 kg.
It is unwise to move large bottles of hazardous liquids when students are about in large numbers.
Chemicals
Section 7 - Page 22
© CLEAPSS 2009
Dispensing liquids
Particular care is needed with 2.5 litre bottles; splashing can easily occur, which is why appropriate
PPE must be worn. After pouring, the necks of bottles should be wiped carefully.
!Do not pour from a large bottle into a measuring cylinder. When making up solutions, it is better to
pour the liquid into a suitable-size beaker or a large measuring jug (which has a handle) before
measuring the required volume with a measuring cylinder.
!Do not dispense liquid in the chemical store unless you have the right facilities. Eg, fume cupboard,
bench, ventilation, etc.
Care should be taken in pouring from a beaker: a
funnel should be used when filling a narrownecked bottle and the use of a glass or plastic rod
with the beaker helps to avoid spills as shown in
the diagram. In all cases it is worth having a tray
to catch any spills.
Tray to catch spills
Transporting chemicals
Transporting small amounts of laboratory chemicals between school sites is not uncommon and
science staff may be concerned about the legal implications of using public roads. The legislation is
very complicated but with common sense it can be accomplished. This is discussed in detail in section
20.7 (Chemicals: transport on public roads).
If a laboratory is sited in another building within the school grounds and chemicals need to be
transported there, a standard laboratory trolley may be unsuitable as the wheels are too small. A sack
trolley with a box container secured to the trolley with elastic ties can be used.
7.5
Disposal of chemicals
There have been many changes in waste disposal legislation in the past few years which has reflected
the public’s, the waste industry’s and the European Community’s concerns. In addition, there are
differences in perception between the disposal of household chemicals from homes and similar
chemicals from a school. The introduction of the word ‘chemical’ when disposing of these substances
can be very emotive but not necessarily rational. At home, white spirit contaminated with paint is
washed down the sink. At school, technicians can agonise over the removal of 50 cm3 of cyclohexane
from the nylon-rope experiment.
It is important to distinguish between two types of waste, which are often governed by quite separate
regulations. Waste disposed of by collection is generally solids and non-aqueous liquids. Effluent is
solutions in water, which is disposed of via the drains.
Further information on the legal interpretation that CLEAPSS as adopted for the handling of chemical
waste from school science departments, then turn to the Appendix 7C at the end of section 7.
Interpreting the W Hazcard
In the last edition of Hazcards, a new system of codes was introduced, ie, W1, W2, etc. The information
can be found on the Chemical waste from school and college laboratories card (‘W’ card) as well as on
individual Hazcards but the limited space available on individual Hazcards restricts the inclusion of
detailed advice on separation and treatment techniques. It is important to make use of the ‘W’ card.
© CLEAPSS 2009
Table 7.4
Section 7 - Page 23
Chemicals
W Hazcard summary
Code
What type of waste?
Method of disposal
W1
Surplus and unwanted stocks of hazardous
chemicals (ie, those carrying a hazard warning
symbol). Expiry dates on chemicals are not always
relevant to schools.
Store for removal by a Registered
Waste Carrier. There is a list in
CLEAPSS guidance leaflet PS5.
Collections may happen once every
5 to 10 years.
W2
Small quantities of hazardous waste (leftovers from
experiments, etc) that must not be disposed of and
cannot be treated or recycled. All schools should
have separate containers for:
Store for removal by a Registered
Waste Carrier. Some may be bulked
together. These containers should be
removed each year. The school
management should already be
arranging for the removal of other
hazardous waste such as fluorescent
lights and computer monitors. Chemical
waste could be removed at the same
time by the same company but, if this is
not possible, a list of authorised waste
companies is given in guidance leaflet
PS5.
•
broken thermometers and other bits of mercury
and its compounds,
•
hydrocarbon waste,
•
lead and its compounds ( and cadmium and
cadmium compounds).
Larger schools may need additional containers for:
•
organohalogens,
•
silver residues.
W3
Small quantities of waste that could be recycled with
little effort or reused.
Recycle (details may be provided on the
Hazcard).
W4
Small quantities of waste that react with alkalis.
Add slowly to 1 mol dm-3 sodium
carbonate solution. Heat may be
produced. The resulting solution should
be tested for alkalinity with any
acid/base indicator and, when just
alkaline, poured down a foul-water drain
with further dilution.
W5
Small quantities of waste that react with acids.
Add slowly to 1 mol dm-3 ethanoic acid
solution. Heat may be produced. The
resulting solution should be tested for
acidity with litmus solution and, when
just acidic, poured down a foul-water
drain with further dilution.
W6
Small quantities of volatile waste.
Burn, evaporate or vent the material in a
working (preferably) ducted fume
cupboard or out in the open if safe to do
so.
W7
Small quantities of hazardous waste that may be
disposed of via the drainage system
Dilute in water to below the
concentration given in the right-hand
column of the table on Hazcard W.
W8
Low-hazard solid waste and small quantities of
hazardous waste that may be disposed of via the
normal refuse.
Low-hazard solids can be placed in
normal refuse. This may also be done
with chemicals with hazard warnings if
they are at concentrations below the
level stipulated in the table on Hazcard
W BUT ONLY IF DILUTION HAS
HAPPENED DURING THE ACTIVITY
(ie, you must not dilute them
deliberately for disposal purposes).
W
Spec
Substances with special disposal requirements.
The method of disposal will be
described on the Hazcard.
Chemicals
Section 7 - Page 24
© CLEAPSS 2009
This flowchart provides a useful procedure for deciding on how to dispose of waste chemicals.
© CLEAPSS 2009
Section 7 - Page 25
Chemicals
Managing chemical waste
It is not difficult to manage the amount and complexity of chemical waste disposal in schools provided
some straightforward principles are put into place. Not only will these principals help control waste
disposal they will also avoid technicians carrying out a lot of unnecessary work. Science staff may be
fearful that class practical work may produce large amounts of waste chemicals for disposal, and may
consider restricting the amount of practical work. However, this would be a mistake since teachers and
pupils engaging in high quality practical work is one of the key features of a good science education.
The aim of the principles is to, wherever possible avoid the need to dispose of waste / effluent, or at
least minimise it. The principles we have found to be useful are:
a. Avoid buying
large quantities
Although larger quantities are often cheaper per unit amount, they need to be
stored and, if the curriculum changes, you may end up very expensive disposal
problem. Check stock levels before ordering. The most useful rule is don’t buy more
than you need for between 1 and 2 year’s supply. With some chemicals used only
in small quantities, this will not be possible, but this is unlikely to lead to a significant
problem.
b. Avoid using
too much
Pupils are not experts in chemistry and frequently use more of a chemical than is
really required. For example, when making copper(II) sulfate crystals from
copper(II) oxide, they will continue to add more and more copper(II) oxide than is
required because, even at high temperatures, the reaction with dilute sulfuric(VI)
acid is not instantaneous. Clear instructions can overcome this tendency.
c. Avoid poor
instructions.
Following on from b, published worksheets and textbooks often provide vague
instructions, eg, “add a spatula-full of copper oxide”. What size is the spatula? How
full is full. Give clear guidance
d. Minimise
concentration
of solutions
Reduce the concentration (see L195, Safer Chemicals, Safer Reactions) or working
on a small scale (see guide L215, Microscale Organic Chemistry).
e. Make the
product of one
experiment the
starting point
for another.
Lead(II) chloride, bromide or iodide from precipitation reactions could be filtered off,
washed, dried and then used in electrolysis. Or in post-16 work, nitrate methyl
benzoate and then reduce the methyl 3-nitrobenzoate to 3-aminobenzoic acid; (see
CLEAPSS guide L195, Safer Chemicals, Safer Reactions).
f. Recycle
chemicals
where possible.
Copper sulfate crystals prepared one year could be re-used to make copper sulfate
solution the next year. If you have sufficient experience or skills, recover solvents by
distillation (but not those which easily form peroxides, unless first tested). (W3 on
Hazcards)
g. Avoid or
reduce
contamination
leading to
waste
a) Put out only the amount needed for a lesson, not the whole stock bottle.
b) Give each pupil a known mass or volume sufficient for the experiment. This
requires efficient co-ordination between teacher and technician.
Chemicals
h. Manage the
end of lessons
Section 7 - Page 26
© CLEAPSS 2009
Clearing up at the end of a lesson is often done in a rush. Pupils may just pour all
sorts of chemicals together into a chemical ‘cocktail’ that could continue to react
and give off hazardous fumes. Glassware can become so stained that cleaning it
then becomes a major operation.
Clearing away should be incorporated into lesson planning but does not need to be
complicated or time-consuming. For example, pupils could be instructed to pour
their used reaction mixtures into a large beaker containing a neutralising reagent or
to tip solutions containing pieces of metal through a sieve. The technician’s work is
then much less onerous and, more importantly, likely to be less hazardous.
i. don’t accept
gifts
Think very carefully about accepting chemicals from a school which is closing down,
and especially from an industrial unit which is clearing out old stock. The rule of
thumb is don’t accept such gifts.
Even when every effort has been made to prevent waste in the first place, the sheer numbers of pupils
involved can lead to large amounts of waste being generated. Careful planning will help but cannot
eliminate the disposal issue altogether. The main solution is to restrict the amount of chemicals. This
may require simple action to be taken such as limiting the number of pieces of metal available to each
group of pupils in the class. For more complex situations, the teacher could calculate the required
reacting quantities from the balanced chemical equation (and all teachers of chemistry should be able
to do this!) - pupils can then be given only a slight excess of one of the chemicals - just enough to
ensure that any reaction is ‘complete’.
Clearly this requires advance preparation and good co-operation between teachers and technicians but
the advantages, in terms of saving on: the amount of waste produced; the effort required in dealing with
it; the use of resources and the impact on the environment, far outweigh the disadvantages.
Some examples of managing the disposal of some commonly used,
particular chemicals
•
The following examples are described.
•
Preparation of copper(II) sulfate(VI) crystals from copper(II) oxide.
•
The thiosulfate / acid reaction.
•
The nylon rope trick (using cyclohexane or petroleum spirits).
•
Activities involving testing alkenes for unsaturation.
•
The aluminium / iodide reaction, when it does not work.
•
Yellow lead iodide in test tubes.
•
Waste from large scale Quickfit oxidation of alcohols.
•
Making hydrogen halides from the potassium halides and concentrated acids.
•
Waste from reacting metals with acids.
•
The Thermite reaction, when it does not work.
© CLEAPSS 2009
Section 7 - Page 27
Chemicals
Preparation of copper(II) sulfate(VI) crystals from copper(II) oxide
Technicians usually have to deal with a basin full of apparatus and filter papers, the latter usually
containing far too much copper(II) oxide.
Prevention, Limitation or Control
Dealing with the worse situation
•
Wear eye protection.
•
Provide each group of students with
just an excess of copper(II) oxide
[2 g of copper(II) oxide reacts with
25 cm3 of 1 M sulfuric(VI) acid].
•
•
•
•
Filer papers can go in the bin.
•
Wear eye protection.
Collect all the filter papers together and leave them a
labelled beaker of in 1 M sulfuric(VI) acid overnight
(or warm the mixture).
Decant the blue solution into a bucket of cold water
and pour this down the foul water drain. Or you can
leave the solution to evaporate and recycle the
crystals.
The paper can be placed in the waste bin.
The thiosulfate / acid reaction
While the mixture of apparatus and chemicals is waiting to be cleaned, it gives off sulfur dioxide
(affecting the lungs) and leaves colloidal sulfur, which is difficult to remove from the glass.
Prevention, Limitation or Control
Dealing with the worse situation
•
•
Wear eye protection.
•
Immediately place the equipment and/or solution in the
fume cupboard and, wearing gloves, remove and rinse
the glass apparatus.
•
Immediately wash the glass with soap and a brush to
remove the colloidal sulfur. Wash further in the
dishwasher.
•
To any solution in the fume cupboard, add an indicator
and stir in 2 M sodium hydroxide solution until the
indicator changes colour.
•
The basin and its contents can now be removed from
the fume cupboard, poured into buckets of water and
all poured down the foul water drain.
•
Provide each group of students with
a beaker containing 1 M sodium
carbonate solution with an indicator.
Pupils should place the contents of
their reactions immediately into the
coloured sodium carbonate solution
and rinse their containers with water.
•
Have ready some washing soda
which can be added if the indicator
changes colour and solution
becomes acidic.
•
Consider scaling down the reaction.
See guide L195, Safer Chemicals,
Safer Reactions.
The nylon rope trick (using cyclohexane or petroleum spirits)
Even if only small amounts are used for a demonstration, there is quite a cocktail of chemicals present.
If it is carried out by students then there will be a larger volume to dispose of.
Clearing up the demonstration
Clearing up a class experiment
•
Wear goggles and use a
fume cupboard.
•
Stir the contents vigorously and then
remove the solid, wrap it in paper and
place it in the waste bin.
•
Place the mixture of liquids on a
metal tray in the fume cupboard and
allowed to evaporate.
•
•
•
•
•
•
•
•
•
•
Wear goggles and use a fume cupboard.
Fill your largest beaker half full with the waste.
Stir well and remove the solid.
Wrap this in newspaper and place it in the waste.
Place the liquid in your largest separating funnel.
Remove the lower layer to one labelled beaker
(aqueous layer) and remove the top layer into an
another labelled beaker.
Repeat this separation procedure with more of the
waste if necessary.
Pour the lower aqueous layer down the foul-water
drain with plenty of water.
Place the organic liquid in bottle labelled ‘hydrocarbon
waste, highly flammable’ and store this in the
flammable cabinet.
Add this bottle to the next collection of hazardous
waste.
Chemicals
Section 7 - Page 28
© CLEAPSS 2009
Activities involving testing alkenes for unsaturation
There are many chemicals involved here and if cyclohexene is used, the smell can be quite
overpowering.
Prevention, Limitation or Control
Dealing with the worse situation
•
•
Wear goggles, nitrile-disposable gloves and use a
fume cupboard.
•
Add water to the ice- cream container. Ensure the test
tubes are immersed, emptied and removed to another
basin to be washed.
•
Add about 10 g of sodium carbonate crystals and an
acid base indicator to the container. If the indicator
shows the liquid is acidic, add more sodium carbonate
with stirring until is alkaline.
•
If the volume of hydrocarbons in the waste appears to
be less than about 75 cm3 then pour the contents onto
a metal tray in the working fume cupboard and allow
the hydrocarbons to evaporate. The aqueous liquid
that remains can be poured down the foul water drain.
•
If the volume of hydrocarbons used is greater than
about 75 cm3, then place the liquid in your largest
separating funnel. Remove the lower layer to one
labelled beaker (aqueous layer) and remove the top
layer into an another labelled beaker.
•
Repeat this separation procedure until all the waste
has been separated.
•
When complete, pour the aqueous layer down the
foul-water drain.
•
Pour the organic liquid in a bottle labelled
‘hydrocarbon waste, highly flammable’ and store this
in the flammable cabinet.
•
Add this bottle to the next collection of hazardous
waste.
•
Ensure that pupils work on a small
scale. The instruction in PS67-01
will help.
Pupils should take the test tubes to
the fume cupboard and place them in
an ice-cream container (or similar
plastic box).
The aluminium / iodide reaction, when it does not work
If the mixture fails to ignite in the fume cupboard, then, if not dealt with immediately, the reaction
catches fire and harmful iodine vapour is given off. It must not be carried to another room.
Prevention, Limitation or Control
Dealing with the worse situation
•
•
Do not abandon the experiment; deal with it straight
away.
•
Wear goggles, wear chemically resistant gloves. Use a
fume cupboard.
•
Place a large beaker of 1 M sodium carbonate solution
in the fume cupboard. Add the mixture and stir to
remove dissolve iodine. Once it is a pale yellow colour,
flush the mixture down the foul water drain with lots of
water.
•
Make sure iodine is finely divided
before mixing it with the aluminium
powder.
Add soapy water so that a section of
the mixture gets thoroughly wetted to
initiate the reaction.
© CLEAPSS 2009
Section 7 - Page 29
Chemicals
Yellow lead iodide in test tubes
Lead and the compounds are toxic materials and the test tubes are stained.
Prevention, Limitation or Control
Dealing with the worse situation
•
•
Wear gloves. Wear eye protection.
•
Filter the suspension and retain the solid.
•
Let the solid dry overnight and place it in labelled
bottle ‘lead waste’.
•
Place the test tubes in a large beaker and add boiling
hot water (which dissolves any remaining lead iodide).
Remove the test tubes with tongs and rinse under the
tap. (You may need to brush them!)
•
Pour water down the foul-water drain.
•
Use a microscale technique using
one or two drops of the reagents on a
plastic sheet or spotting tile. Use low
concentrations, eg, 0.005 M lead
nitrate(V).
The liquids can then be just flushed
away.
Waste from large scale Quickfit oxidation of alcohols
This reaction produces a dark green solution but it is not clear whether all of the dichromate(VI) has
reacted. If the glassware is left connected for any time, the joints seize up!
Prevention, Limitation or Control
Dealing with the worse situation
•
•
Wear chemical-resistant gloves. Wear eye protection.
Use a fume cupboard.
•
Disconnect the glassware.
•
Add water to pear-shaped flask and pour the contents
into a holding beaker.
•
All the glassware should be rinsed.
•
For every gram of sodium dichromate(VI) used by
students, add 1 g of sodium metabisulfite. This will
convert all the dichromate(VI) into chromium (II) ions.
•
Stir, leave for 10 minutes and pour this with lots of
water down the foul-water drain.
•
Once the equipment is hand-hot,
students should disconnect it, rinse
the flask and the contents with water
into the beaker supplied.
Rinse all the other glassware and
place it into a basin for washing.
Making hydrogen halides from the potassium halides and concentrated acids
This activity will involve bromine, iodine, sulfur, sulfur dioxide and hydrogen sulfide. There will be
unreacted concentrated sulfuric(VI) and phosphoric(V) acid.
Prevention, Limitation or Control
Dealing with the worse situation
•
•
Use a fume cupboard. Wear chemical-resistant
gloves. Wear eye protection.
•
Collect all the test tubes together in ice cream tubs
half filled with water.
•
Add washing soda and the iodine will be removed.
•
Lift, empty, and re-immerse the test tubes regularly
until nearly all the iodine is removed.
•
Test the alkalinity of the solution so ensure it continues
to be alkaline.
•
The alkaline solution can be poured down the foulwater drain with plenty of water.
•
You may have to use a test tube brush on some test
tubes with stubborn iodine stains.
•
Pupils should be given an ice cream
container (or similar), half full of 0.5
M sodium carbonate solution
coloured with an acid/base indicator,
into which they can put the test tubes
once they have cooled.
The alkaline solution can be poured
down the foul-water drain with plenty
of water.
Chemicals
Section 7 - Page 30
© CLEAPSS 2009
Waste from reacting metals with acids
You are confronted with a load of test tubes containing unreacted acids, salt solutions and unreacted
metals such as copper, iron, magnesium, zinc and lead. If left, iron will stain glass, giving you more
work.
Prevention, Limitation or Control
Dealing with the worse situation
•
•
Wear chemical-resistant gloves. Wear eye protection.
•
Gather all of the test tubes into one (or more) large
plastic container.
•
Place the container in the sink and run water into it to
dilute any remaining acid.
•
Allow the container to overflow, pick out and empty the
test tubes and put these to one side for further
washing.
•
Decant the liquid in the container down the foul-water
drain with lots of water. (Don’t worry if tiny bits of metal
flow away.)
•
Using a magnet inside a small plastic bag, gently
rummage the magnet through the debris in the plastic
container and remove the iron to a paper towel. Ignore
any small pieces of copper that might be collected.
Repeat this until most of the iron is removed.
•
Use forceps to remove the zinc granules and
soft lead foil.
•
Now add 2 M hydrochloric acid to dissolve any
residual zinc, iron or magnesium.
•
If you have not used lead shot, you are left with copper
turnings. Dry and recycle.
•
If you have used lead shot then ‘volunteer’ pupils can
separate lead shot from copper turnings using forceps.
Supply pupils with very small
amounts of the metal, eg, two copper
turnings, one zinc granule, one piece
of lead foil, 0.5 of iron filings and
1 cm of magnesium ribbon. This
takes a long time in preparation but
clearing up will be much shorter.
•
Magnesium will react completely.
•
Zinc granules and lead foil can be
picked out with forceps, dried on
paper towels and recycled.
•
Iron can be removed with a magnet
covered in cling film or plastic bag so
it is easy to release the iron
afterwards. This can be thrown away
in the waste.
•
Leave any copper for drying and
recycling.
The Thermite reaction, when it does not work
Dealing with the worse situation where the powders are just mixed together.
•
Wear chemical-resistant gloves. Wear eye protection.
•
If barium nitrate(V) is used in the igniter. Add the contents to a litre of water and stir to dissolve the
barium nitrate(V).
•
Let the solids settle and decant the liquid away down the foul water drain.
•
Place the solids in a bag in a waste bin.
•
If barium peroxide is used in the igniter. Add the contents to a litre of 1 M sulphuric acid and place
the mixture on a stirrer. This should be done in a fume cupboard with no sources of ignition around.
Magnesium will react with the acid giving off hydrogen. This will be quick. Barium peroxide will react
slowly to give of oxygen. Aluminium powder is passive in sulfuric(VI) acid.
•
Let the solids settle and decant the liquid away down the foul water drain.
•
Place the solids in a bag in a waste bin.
© CLEAPSS 2009
7.6
Section 7 - Page 31
Chemicals
Making solutions and reagents
Commonly technicians are asked to prepare a solution or reagent to a specific concentration, where the
concentration can be expressed in a variety of different forms. Sometimes it is simply described as
‘dilute’ or ‘concentrated’, although this is not very helpful for risk-assessment purposes. The CLEAPSS
Recipe Cards (on the secondary resource part of the web site and the CLEAPSS Science Publications
CD-ROM) give clear instructions for making up the more common solutions used in school science,
together with risk assessments for handling them. Many reagents and preparations used in biology
teaching are included. Where a solution is not described in the Recipe cards a little arithmetic may be
required, as explained later in this section.
!When making up reagents or solutions to a published formula, unless the instructions say
otherwise, dissolve the chemicals in the order given.
The following subsections are included within this section.
•
•
•
Making up a solution.
Solution units.
Calculations for making solutions of solids.
•
•
•
Calculations for making solutions from liquids.
Other units of concentration.
Saturated solutions.
The basic process of making a solution
Making a 1 litre solution of 0.1 M copper sulfate(VI) is illustrated in the following sequence.
Use the recipe card to find the mass
of copper sulfate(VI) required. In this
case it is 24.96 g.
Set up the stirrer. A laboratory jug is
filled to about 800 ml with pure water.
Insert the stirrer bar and start sitting.
The solid is added to the water.
Wash the weighing bottle with a wash
bottle allowing the drips to run into the
stirring solution.
When the solid has dissolved, stop
the stirrer and allow the water to
come to rest. Add more pure water.
This water is added up to the 1 litre or
1000 ml mark.
The solution is poured carefully into the bottle. It is
possible to pour from a laboratory jug straight into a bottle
but using a funnel and a guide rod minimises spills.
Make sure the top of the bottle is secure and a label is
attached. This should carry the hazard waning but this
solution is low hazard.
Chemicals
Section 7 - Page 32
© CLEAPSS 2009
Units encountered when making solutions
The commonly used units when making solutions are as follows.
mol
Also often referred to as the mole. It is the amount of the (dissolved) substance. The chemistry and the
language used to describe that chemistry is complex. A useful rule of thumb is that a mole of a
substance is its molar mass in grams. So, for example, sulfuric(VI) acid is has a molar mass of 98.
Therefore 98 g of it contains 1 mole of sulfuric (VI) acid entities.
The word entities takes some understanding; it includes any small particles, whether they are atoms,
groups of atoms, molecules, ions or radicals. It can be said that a mole of sulfuric(VI) acid (H2SO4)
contains:
•
one mole of sulfuric(VI) acid entities (H2SO4), (in this case molecules),
•
2 moles of hydrogen entities, (in this case hydrogen atoms),
•
1 mole of sulfate(VI) entities, [in this case sulfate(VI) groups],
•
1 mole of sulfur entities (in this case atoms), or
•
4 moles of oxygen entities (in this case atoms).
In water, 1 mole of sulfuric(VI) acid splits up in water into 2 moles of hydrogen ions and 1 mole of
sulfate(VI) radicals. So a 1 M solution of sulfuric(VI) acid in water produces twice as many (ie, 2 moles)
of hydrogen ions.
So a mole is proportional to the number of specified elementary entities of that substance. This is rather
like ‘the dozen’ where one counts in 12s. But these entities are so small that the number has to be
much larger. The proportionality factor is the Avogadro constant1 (NA). This number is the number of
-1
atoms in exactly 12 grams of 12C, ie, NA = 6.022 x 1023 mol .
mol dm-3, mol l-1, M or mol/l
There are several ways in which the strength of a solution may be written; the most important is mol
dm-3 (moles per cubic decimetre is the preferred description but moles per litre is equally correct).
Sometimes the word ‘molar’ is used (incorrectly) with the same meaning. Although the preferred
abbreviation is mol dm-3 as above, you will often see M, and, sometimes, mol/dm-3 or mol/l. In this
Handbook we use ‘M’ for mol dm-3 and ‘ml’ for cm3.
This measurement shows how many times the molar mass in grams (how many moles) of a chemical is
dissolved in one litre of the finished solution. The cubic decimetre (dm3) and the litre (l or L) are the
same. The symbol M should always be followed by the chemical formula to remove any doubt over the
meaning of the concentration but, where there is only one possible formula, it is frequently omitted.
For example, a solution of sodium chloride of 1 mol dm-3 concentration will have 58.4 g of solid (the
formula mass in grams) dissolved in water to make 1 litre.
In making up solutions always dissolve the solid chemical in too little water to start with and then dilute
it to the volume required. (Because taking 1 litre of water and dissolving 58.4 g of sodium chloride in it,
will produce a solution with a volume greater than 1 litre and therefore not be 1 M.)
1
The term ‘Avogadro number’ should not be used.
© CLEAPSS 2009
Section 7 - Page 33
Chemicals
Calculations for making solutions of solids
Formula masses are given on the bottles of chemicals bought from most suppliers. It is best to use this
figure as the value can vary with the form of the chemical. For example, anhydrous sodium carbonate
has a formula mass of 105.9 g whereas the hydrated form (washing soda) has a formula mass of
286.1 g.
Dissolving 105.9 g of the anhydrous sodium carbonate or 286.1 g of the hydrate to make 1 litre will give
a solution of 1 M.
If quantities of solutions different from 1 litre are required or if the solution strength is to be 2 M or
0.1 M, etc, the mass of solid necessary should be looked up in Recipe Cards or calculated as below.
There are two standard methods.
a) Starting from the formula mass given on the bottle
Using sodium chloride (molar mass 58.4 g mol-1) as the example.
To make:
Amounts needed
(The molar mass of sodium chloride is 58.4 g mol-1.)
1 litre of 1 M sodium
chloride solution
58.4 g of sodium chloride made up to 1 litre of solution
2 litre of 1 M sodium
chloride solution
2 × 58.4 g of sodium chloride = 116.8 g, made up to 2 litres of solution
250 ml of 1 M sodium
chloride solution
0.25 × 58.4 g (because 250 ml is 0.25 litre) of sodium chloride = 14.6 g,
made up to 1 litre of solution
1 litre of 0.2 M sodium
chloride solution
0.2 x 58.4 g of sodium chloride = 11.68 g, made up to 1 litre of solution
500 ml of 0.2 M sodium
chloride solution is
required
The adjustments are made for each in turn.
For 1 litre of 1 M (NaCl) solution, the mass needed = 58.4 g
So for 500 ml of 1 M (NaCl) solution, the mass needed = 58.4 ÷ 2 g = 29.2 g
So for 500 ml of 0.2 M (NaCl) solution, the mass needed = 29.2 × 0.2 g = 5.84 g
b) Using a formula:
Mass required (g) = Formula mass (g mol-1) × Concentration required (mol L-1) × Volume required (L)
Calculations for making dilute solutions from liquids
[eg, sulfuric(VI) acid]
Calculations of this sort are more complicated because these liquids are often not the same density as
water, are supplied as solutions, and may lose the active ingredient during storage, eg, concentrated
hydrochloric acid is a 35 - 36% (w/w) solution in water which gives off hydrogen chloride fumes.
Rounding errors in calculations may imply different final concentrations which is often a source of
confusion, but which will have little effect on the practical activity itself. For extremely accurate work,
any solution would have to be standardised against a recognised standard solution (See Recipe cards
for standard solutions and section 13.)
Chemicals
Section 7 - Page 34
© CLEAPSS 2009
For most purposes, the simplest and the quickest method to make these solutions is to use Recipe
cards. The following table, which contains the concentration of the concentrated acids, is also useful.
Table 7.5
Concentrations of chemicals purchased as liquids
Chemical
Standard description
Concentration as
purchased
/M
Volume to make 1 litre
of 1 M solution / ml
Ammonia
35% (w/w) or ‘880’
18.1
55
Ethanoic aid
99.5 (w/w)
17.4
57
Hydrochloric acid
37% (w/w)
11.7
84
Hydrogen peroxide
100 ‘vol’
8.3
120
Methanal
40% (w/v)
13.3
75
Methanoic acid
90% (w/w)
23.9
42
Nitric acid
70% (w/w)
15.8
62
Phosphoric acid
(orthophosphoric)
85% (w/w)
90% (w/w)
14.7
16.1
68
62
Sodium chlorate(I)
10 to 14% (w/w)
available chlorine
1.4 to 2.0
714 to 500
Sulfuric(VI) acid
98% (w/w)
18.4
54
Once this value is known, it is fairly easy to work out how much is needed to make any other solution.
For example, the table shows that sulfuric(VI) acid is supplied at a concentration of 18.4 M so every
litre has 18.4 moles in it. To make 1 litre of 1 M H2SO4 solution, only 1 mole of acid is needed which is
1 litre ÷ 18.4 or 54 ml. Therefore 54 ml of concentrated acid is needed to make 1 litre of 1 M H2SO4.
!Don’t forget! Always to add acid to water!
Other units of concentration
Mass per unit volume - grams per litre (g l-1) [also written as g dm-3 or g/l]
To make up solutions to a particular concentration in these units, the number of grams of solid stated
are dissolved in rather less water than one litre and then diluted to one litre. To make up a volume other
than one litre, it is necessary to multiply (or divide) the number of grams by that volume.
Mass of solid required / g = Required concentration / g l-1 × Volume required / L
Mass of solid required / g = Required concentration / g l-1 × Volume required / ml ÷ 1000
Very occasionally solutions are given in grams per 100 ml or even grams per ml (g ml-1). It is simply the
volume in which the given amount is dissolved that is different in these two cases.
© CLEAPSS 2009
Section 7 - Page 35
Chemicals
Percentage
17
A % sign means a fraction with 100 underneath (ie, 100 is the denominator), eg, 17% = 100
. There are
three different ways of expressing concentrations as percentages: % w/v, % w/w, and % v/v.
a. % weight for volume, % ‘w/v’
If only a percentage is given, with no w/w or w/v, etc, it means percentage ‘weight for volume’. This is
not a helpful way of describing a solution. This measurement indicates the number of grams of a
chemical dissolved in 100 ml of the solvent. So, to make up a 10% ‘w/v’ solution of a solid, 10 g should
be dissolved in about 70 ml of solvent and the solution then made up to 100 ml. The formulae below
give the mass of solid needed to make the solution.
Mass of solid required / g = Required concentration / % ‘w/v’ × Volume required / L × 10
Mass of solid required / g = Required concentration / % ‘w/v’ × Volume required / ml ÷ 100
It is more difficult to work out how to dilute a liquid such as ammonia to a particular percentage ‘w/v’ but
it will usually be close enough to use the following approximate method.
The concentration of the liquid that to be diluted may be found from suppliers’ catalogues as % w/v and
then the formula below is used.
Required concentration / % ‘w/v’
Mass of liquid to be diluted / g = Concentration of starting liquid / % ‘w/v’ × Volume required / L × 1000
Required concentration / % ‘w/v’
Mass of liquid to be diluted / g = Concentration of starting liquid / % ‘w/v’ × Volume required / ml
Finally, this mass is taken as the volume of the liquid to be diluted in ml. (Strictly it is necessary to
divide by the density to get the volume but it will be near enough 1 g ml-1.)
b. % weight for weight, % w/w
This is sometimes used by suppliers to describe the concentration of liquid chemicals such as acids. It
indicates the percentage by weight that the chemical makes of the whole. So 98% w/w sulfuric(VI) acid
has 98 g of pure acid in every 100 g of the liquid. School staff are unlikely to be asked to make up
solutions to this measurement.
c. % volume for volume % v/v
This measurement is sometimes used for approximate dilution of liquids such as sulfuric(VI) acid or
ammonia and it simply indicates the percentage of liquid (assuming the usual concentration of stock)
that is diluted to the final volume. The following formulae may be useful.
Volume of liquid to be diluted / L = Required concentration / % ‘v/v’ × Volume required / L × 10
Volume of liquid to be diluted / ml = Required concentration / % ‘v/v’ × Volume required / ml ÷ 100
Parts per million (ppm)
Commonly, this unit is used to describe the ‘strength’ of disinfectant solutions containing ‘X’ ppm of
available chlorine, a term derived from the chlorine liberated from a solution of sodium chlorate(I) (also
know as sodium hypochlorite solution) via the following chemical equation.
NaClO(aq) + 2HCl(aq) → NaCl(aq) + H2O(l) + Cl2(g)
The term ‘ppm’ represents the mass unit of chlorine in one million mass units of solution. This is most
easily thought of as 1 mg of chlorine in 1 kg of solution.
So, a solution containing 1000 ppm of available chlorine (as needed for general disinfection) has
1000 mg, or 1 g, of chlorine in 1000 g of solution and, as the density of sodium chlorate(I) solution is
close to 1 g cm-3, the statement becomes 1 g of chlorine per litre of solution.
Chemicals
Section 7 - Page 36
© CLEAPSS 2009
Sodium chlorate(I) solutions are usually supplied as 10 - 14% (w/w or w/v) available chlorine. This
means that 100 g (or 100 ml) of the solution could liberate 10 - 14 g of chlorine. For general disinfection
purposes (and to keep the maths simpler) we treat purchased solutions as having 10% available
chlorine
So, 1 litre of the concentrated solution should liberate at least 100 g (ie, 1 × 105 mg) of chlorine.
To prepare a solution containing at least 1000 ppm available chlorine from the concentrated laboratory
reagent, it must be diluted 100 times, eg, 10 ml of solution should be diluted with water to give 1 litre of
solution. This and other dilutions are listed in Table 7.6.
Table 7.6
Strengths of sodium chlorate(I) solutions
Application
Working strength / ppm
Volume of 10 - 14% sodium chlorate(I)
solution to be diluted to 1 litre / ml
General
1000
10
Discard pots
2500
25
Blood spills or dirty
conditions
at least 10000
100 or more
Domestic bleach is not recommended as a starting solution because it will already be diluted and may
well be relatively expensive. However, details of the concentration should be on the bottle and, if it is
used, appropriate alterations will have to be made to the dilutions above.
‘Vol’ strengths of hydrogen peroxide
Hydrogen peroxide solution strengths are commonly expressed as so many ‘vol’, short for ‘volume
strength ratio’. This is an old term still used in the UK and refers to the volume of gaseous oxygen
available from a unit volume of hydrogen peroxide solution measured at 0 °C and one atmosphere. The
following equation represents the reaction:
H202(aq) → 2H2O(l) + O2 (g)
So 20 ‘vol’ hydrogen peroxide provides 20 cm3 of oxygen from 1 cm3 of solution and 100 ‘vol’ hydrogen
peroxide solution provides 100 litres of oxygen from one litre of solution.
It might be necessary to convert this concentration to moles per litre. As 1 mole of gas occupies
24 litres at room temperature and pressure, 100 litres of oxygen must contain 4.17 moles (100 ÷ 24)
which must, in turn, come from 4.17 × 2 or 8.33 moles of hydrogen peroxide. Hence 100 ‘vol’ is an
8.33 M solution of hydrogen peroxide, 20 ‘vol’ is a 1.67 M solution and 10 ‘vol’ is 0.83 M, or,
concentration of solution / M =
‘vol strength’
.
12
Saturated solutions
Before preparing a saturated solution of a chemical, try to find out its solubility. Some chemicals are
very soluble and, if too much water is used to start with, it is possible to run out of solid trying to make
the solution. Recipe Cards give quantities of chemicals required for making given volumes of saturated
solutions that are most likely to be required. For other solutions, Nuffield Advanced Science Books of
Data or the reference book Kaye & Laby1 (there may be a copy in the Physics Department) may give
the solubilities. CLEAPSS has reference books as well and you can contact the Helpline.
1
Eg, G W C Kaye & T H Laby, Tables of Physical and Chemical Constants, Longman, 1973 (but any edition will do). It
can also be accessed electronically on www.kayelaby.npl.co.uk.
© CLEAPSS 2009
Section 7 - Page 37
Chemicals
If these books do not give the solubility figure required, then a small-scale test can be carried out first
as follows. Wikipedia is now a good source of information on the solubility of many common chemicals.
•
Weigh roughly 5 g of the solid into a test tube.
•
Add about 2 ml of water, stopper the tube, gently heat the solution in a beaker of boiling water and
agitate the test tube vigorously for several minutes. (If there is still a solid present then carry on
adding 2 ml amounts of water, warming and agitating. Stop doing this when the substance
dissolves.
•
On cooling the solid will probably recrystallise and the solution will be saturated.
•
It is now possible to work out how many ml of water dissolve about 5 g and, from that, how much
solid is needed to make a larger volume of solution. There is no need to throw away the test
solution; add it to the full-scale solution.
If the 5 g of solid has not dissolved completely in the full test tube, start again using 2 g of the solid.
7.7
Dealing with Chemical spills
A spill of a hazardous chemical is an emergency and needs to be dealt with safely and efficiently, using
an established and familiar procedure, as referred to in Hazcards and in this section. This is a
requirement of the Management of Health and Safety Regulations. Teaching staff, technicians and
pupils will need to co-operate and work together to deal effectively with spills so all will need
appropriate training.
•
Teachers need to be familiar with the chemicals they use, how to deal with spills using Hazcards,
and know where the mineral absorbent is kept in the laboratory.
•
Pupils should be taught to deal effectively with minor spills and to report more-hazardous ones
immediately.
•
Technicians need accurate information about the nature of any spill they may have to deal with and
they need to be fully familiar with, and to have practised, the clearing-up procedures.
A spill may occur during a lesson, in the prep room or store or in transit between rooms. The procedure
Dealing with a chemical spill describes how to deal with most large chemical spills. The process can be
summarised as:
•
Assess the nature and extent of the spill,
•
Make the area safe,
•
Absorb the spill,
•
Remove the absorbed spill treat it if necessary,
•
Dispose of the treated spill and materials used,
•
Remove remaining traces of the spill.
Hazcard E summarises the initial action that a teacher or technician needs to take when confronted by
a spill. It says the following:
Spill emergency
Wear goggles and chemical-resistant gloves. Fence off the area and, if any fumes are
causing distress, consider evacuation; see below. If the substance is HIGHLY
FLAMMABLE, switch off all sources of ignition. Ventilate the area of the spill. Do not
put other teachers, technicians or pupils at risk. For liquid spills, evaluate the amount
spilt and the degree of hazard. Paper towels may suffice but, for larger or more
hazardous spills, add the mineral absorbent in your laboratory and summon help. For
further advice on dealing with the mineral absorbent and its subsequent treatment,
consult section 7.7 of the Handbook and, if necessary, phone the Helpline. In
extreme cases, call the fire brigade, asking for the Chemical Incident Unit.
Chemicals
Section 7 - Page 38
© CLEAPSS 2009
It is important that a science department keeps a supply of at least 1 kg of mineral absorbent in every
laboratory and one or more (depending on the layout of the department) spills kits, which are only used
to deal with spills. A spills kit needs to be complete and easily available in the event of a spill. The
contents of general and more specific spills kits are described later in this section.
How hazardous is the spill?
Mercury spills need special treatment and are dealt with separately later in this section.
The questions in the following table can be used to judge whether it is safe to tackle a spill.
What are the
chemical
hazards?
Specific advice on the treatment and disposal of a particular chemical, where it differs
from the general procedure, is given on the relevant Hazard. General advice can be
found on the Emergency E card and is amplified in the section.
How big is
the spill?
Small, low-hazard spills can be absorbed with paper towels that are then rinsed in the
sink and placed in the normal refuse.
Larger spills and small spills of hazardous chemicals can be absorbed on mineral
absorbent, which should be present in every room.
Is it solid or
liquid;
if liquid,
is it volatile?
A dustpan and brush can be used to clear up a solid but take extra care not to raise
dust. It may be necessary wear a dust mask.
For volatile liquids and gases, open the windows to improve ventilation only if this can
be done without putting anyone, including yourself, at risk.
It may be necessary to evacuate the room if, eg, the spill is large, volatile and
CORROSIVE or TOXIC.
In extreme cases, it may also be necessary to call in specialists, generally the fire
brigade1.
What surfaces
have been
affected?
A spill may seep into a rough surface. In extreme cases, the surface (eg, carpet, pupil’s
bag) may need to be discarded once valuable items have been retrieved and cleaned.
Where there is doubt on how to proceed, call the CLEAPSS Helpline. If the spilled liquid produces a
powerful smell, it would be wise to call CLEAPSS
After dealing with a spill, it may be helpful to discuss the incident within the department and to note any
points to avoid in future.
A general procedure for dealing with substantial spills in described on the following page. Copies of the
procedure could be kept with the spills kit and in the departmental safety file.
1
Be warned! As you work in a school and children might be affected, a call to the Fire Brigade will be accompanied by
ambulances, the Police and newspaper reporters.
© CLEAPSS 2009
Section 7 - Page 39
Chemicals
Dealing with a chemical spill
!
1. Manage the incident:
Is the area safe?
Is anyone injured or
suffering?
Have you sent for extra help?
!
!
!
2. Absorb and remove the
spill for treatment.
!
!
!
3. Treat the contaminated
mineral absorbent according
to its properties:
If the area is unsafe, evacuate the room, close
the door, allow any fumes to disperse or call
specialist help.
Treat any injuries.
Spills involving hazardous chemicals: surround
the area with stools, control onlookers an pour
enough mineral absorbent on the liquid spill to
absorb it completely.
If the spill occurs during a lesson: call or
Sweep the dry spill with mineral absorbent into
a bucket.
Wipe over the area so that the lesson may
continue if possible.
Take the absorbed spill with its container to the
prep room for treatment and disposal.
Not water soluble?
Add and equal volume of detergent.
Reacts with alkalis?
Use solid sodium carbonate
unless Hazcards say
otherwise.
!
!
Add water and allow the contents to mix.
If treated with acid or carbonate, check if the spill has been
neutralised. Allow the mixture to settle.
5. Pour away the diluted
mixture with further dilution:
!
!
!
Decant the liquid down the foul-water drain.
Refill the bucket with water and repeat.
If the spill was oxidising or toxic, refill the bucket and pour
away the liquid a further 8 times.
6. Dispose of the residue:
!
Bag up the washed mineral absorbent and dispose of it in the bin.
4. Dilute the treated spill:
!
Return to the spill areas after the lesson and clean thoroughoy, particulalrly if TOXIC or
OXIDISING chemcials were involved.
Chemicals
Section 7 - Page 40
© CLEAPSS 2009
Spills Kits
A spills kit needs some way of absorbing liquid spills. We have found that mineral absorbents are easily
available and work well. The cheapest supply of mineral absorbent is cat litter based on clay. It is inert
to all chemicals in schools and most varieties do not break up into a hard-to-clean-up mud when wet.
Cat litter can be found in most supermarkets. Unless you are familiar with the particular brand, buy a
small, cheap bag first to test its stability when wet before buying larger 10 kg bags. Note that some
clay-based cat litter is calcined and will ‘fizz’ for a short time when applied to an acid but this is not
hazardous. Cat litter will absorb a liquid but will slowly settle out of the mixture if left in a bucket or
similar container. This means that the liquid can be easily decanted off for treatment and disposal and
the damp cat litter can be equally easily disposed of.
Some types of cat litter are based on Fuller’s Earth which is red, but this breaks up when wet.
Other than cat litter its possible to use Vermiculite, which floats in water rather than sinking, making
later separation of the liquid and the vermiculite difficult, and sand1, which does not absorb but adsorbs
which actually means it its relatively poor for the purposes of soaking up a spill. Absorbents based on
recycled paper or sawdust (sometimes sold for dealing with oil spills in garages or for use by caretakers
in cleaning up vomit) are unsuitable for chemical spills as they are both oxidised and combustible.
General spills kit
Contents of the spills kit
•
1 plastic bucket.
•
1 plastic dustpan and brush.
•
3 pairs of splash-resistant chemical-protective gloves (nitrile or natural rubber type; see section
20.12, Gloves).
•
Eye protection to EN166 3 (goggles or a face shield).
•
3 floor cloths (these could be disposable).
•
A pack of plastic ‘pedal-bin’ bags (which fit over a bucket) for the disposal of small amounts of wet
absorbent.
•
1 large chemical scoop.
•
2.5 kg mineral absorbent (divide this up into smaller containers, lighter to carry and handle).
•
0.5 kg of anhydrous, technical-grade sodium carbonate (to neutralise up to 250 ml of concentrated
sulfuric(VI) acid, for example).
•
0.5 litre of neat dispersing agent (ie detergent: ‘Teepol’ is a general-purpose detergent for
laboratories but others will suffice and may be cheaper).
•
0.5 kg of citric acid2 (to neutralise up to 250 ml of concentrated ammonia solution or 2.5 l of 2 M
sodium hydroxide solution).
•
A copy of the procedures to be followed in dealing with a spill.
•
One pair of gloves, goggles, the brush and the dustpan could be kept in the bucket so they can
easily be accessed and brought to the scene of a spill.
NB: Breathing apparatus would be needed to treat large spills of corrosive liquids (eg, if 2.5 l of 880
ammonia was spilled). The fire brigade will be needed. Evacuate the area and consult CLEAPSS if in
doubt.
1
The advantage of clay over sand is that the liquid penetrates into the clay particles, ie, is absorbed, whereas with
sand the liquid is adsorbed onto the surface.
2
Citric acid is chosen because it is a weak acid, a solid and has no odour. Ethanoic acid may also be used.
© CLEAPSS 2009
Section 7 - Page 41
Chemicals
Location of the spills kit
The spills kit should be kept in the internal chemical storeroom, if this is close to and in the same
building as the laboratories. If the department is on separate sites, there should be a kit in each
building. Large departments could keep a complete kit on each storey or group of rooms.
Each laboratory and prep room should have 1 kg of mineral absorbent on hand for teachers to
use in an emergency.
Mercury spills
The following kit should be available whenever mercury (including mercury thermometers) is used.
Instructions for its use follow the contents list.
Mercury spills kit
The special kit for mercury spills should contain the following items.
•
Mercury pooter or syringe (see diagrams).
•
1 small polythene bottle to take recovered mercury.
•
250 ml borosilicate beaker.
•
A mixture of 500 g flowers of sulfur and 500 g calcium hydroxide.
•
1 cheap paintbrush about 3 cm wide.
•
10 wooden spatulas (tongue depressors).
•
2 wooden strips 500 × 30 × 5 mm (eg, old half-metre rules).
Mercury spills procedure
!Do not use a vacuum cleaner or an unprotected vacuum pump to collect spilt mercury.
Recover as much of the split mercury as possible for specialist disposal1.
•
Remove any rings, bracelets, watches, etc, open windows and put on gloves.
•
Gather the bulk of the mercury together using strips of wood (wooden spatulas or half-metre rules).
•
Use a plastic syringe or connect a pooter to a vacuum pump and use it to collect up the bulk of the
mercury. Hold the specimen tube as nearly upright as possible and, if a rotary pump is used, make
sure a trap is fitted in the vacuum line to protect the pump2.
•
Empty the recovered mercury into the bottle prepared in the kit.
To hand vacuum
pump or water-jet
pump
6 mm medium
wall tubing
drawn to 3 mm
at the end
50
l
m
40
m
l
30
m
l
20
l
m
10
m
l
A plastic syringe
25 x 75 mm
speciment tube
or vial
A mercury pooter
1
Mercury waste and any materials or items contaminated with mercury must be sealed in a container and stored for
disposal by a hazardous waste contractor.
2
See section 10.6, Pumps.
Chemicals
Section 7 - Page 42
© CLEAPSS 2009
Clearing remaining small drops
•
Heat some of the lime / sulfur mix with a little water to make a smooth slurry. Spread this over the
contaminated area and leave to dry. It reacts with the mercury to form sulfur compounds.
•
When dry, use the paintbrush to sweep up as much of the mix as possible and put it in the bottle for
mercury waste.
•
Dust the area with some dry lime / sulfur mixture and brush it into any cracks.
And finally
•
Wash all the equipment and arrange for storage of the mercury-bearing waste
•
Bottles of waste should be labelled and stored securely until it is collected for transmission to a
specialist mercury-waste contractor.
Special procedure for schools without mains drainage
Schools not connected to mains drainage systems do not pass solutions or suspensions into a ‘foulwater drain’. A septic tank is usually supplied, in which bacteria digest the effluent (usually
anaerobically). This tank must be considerably larger than one used for a single house, to enable
dilution of waste chemicals to safe levels. Extremely large quantities of oxidising agents or other
substances that kill bacteria could destroy the bacteria. In this case, so long as a clay-based mineral
absorbent is used, the mixture of mineral absorbent and oxidising agent solution should be bagged up
and removed by a hazardous waste contractor.
7.8
Chemical hazards
The Chemicals (Hazard Information and Packaging for Supply) Regulations (commonly known as
CHIP) require suppliers of chemicals to provide information about their hazards to their customers. This
is achieved using a (materials) safety data sheet, with each chemical. You should file these sheets but
they are primarily designed for industry rather than schools so they have limited value in the school
environment. The information required for science departments is summarised on Hazcards.
The CHIP Regulations include hazard data on many hundreds of chemicals and, as well as safety data
sheets, the information may also be available on bottle labels and in catalogues. It’s also, of course,
available on Hazcards. Hazard information may be written and printed in full, it may be conveyed using
a hazard warning sign (see section 7.3 f) or via a numbered code called a risk number which relates to
a risk phrase. A list of all the risk numbers and what they stand for is given in Hazcards and shown in
table 7.14 overleaf.
!The existence of a hazard warning in any of these sources should be treated as a trigger to
consult a risk assessment.
Research into the hazards of chemicals continues all the time and there are regular amendments to the
regulations. Should there be any major changes that affect school chemicals then that information and
its consequences will be published in the CLEAPSS Bulletin. The UK government has now decided to
accept all relevant European recommendations so that there is a wide consensus of agreement on the
hazardous properties of a chemical.
Conflicting hazards and risk phrases
Unfortunately, not all school chemicals with hazards are included in the regulations. In this case,
suppliers are under an obligation to pass on their own hazard information and this can vary between
suppliers, especially if a company is based overseas.
There are three classes of hazard.
© CLEAPSS 2009
Section 7 - Page 43
•
Physico-chemical (eg, explosive, oxidising and flammable hazards).
•
Those which affect health (acute and chronic).
•
Those which affect the environment.
Chemicals
Physico-chemical hazards
Includes explosive, oxidising and flammable hazards.
Explosive chemicals
!These substances “may react exothermically without atmospheric oxygen thereby quickly
evolving gases, and which, under defined test conditions detonate, quickly deflagrate or upon
heating explode when partially confined”1.
The information conveyed by this classification and by risk numbers R1 to 6 is a little extreme for
laboratory use: substances such as ammonium dichromate may explode when handled in bulk but it
would probably be extremely difficult to persuade 200 g in a laboratory bottle to detonate.
Do be very careful with old bottles of picric acid (2,4,6-trinitrophenol) which is normally kept as a wet
paste. It is explosive when dry. There are no recorded incidents of bottles exploding on storage,
however some crystals may have lodged at the top of the bottle and opening the bottle quickly could
decompose the material.
!It would be wise not to open any old bottle of picric acid that may be found hidden in longforgotten cupboards: contact CLEAPSS for advice.
Oxidising chemicals
!These chemicals “give rise to highly exothermic reactions when in contact with… flammable
substances”1. They carry risk numbers R7 to 9.
Certain chlorate(V)s can produce explosive mixtures when mixed with combustible materials. Many of
the nitrates are included in this category and particular care must be taken during disposal. Organic
peroxides, after ignition, can burn without other combustible material present.
Restrictions in Northern Ireland
Many oxidising agents may be held in Northern Ireland only under a controlled substances licence from
the Royal Ulster Constabulary which requires them to be stored securely and for records to be kept of
each usage and disposal.
Table 7.7
1
Risk numbers and the associated risk phrases
Definition from the Chemicals (Hazard Information and Packaging for Supply) Regulations.
Chemicals
Section 7 - Page 44
© CLEAPSS 2009
Physico-chemical Hazards
Hazards which affect health
Hazards which affect the
environment
R1
explosive when dry
R20
harmful by inhalation
R50 very toxic to aquatic organisms
R2
risk of explosion by shock, friction,
fire or other sources of ignition
R21
harmful in contact with skin
R51 toxic to aquatic organisms
R3
extreme risk of explosion by shock,
friction, fire or other sources of ignition
R22
harmful if swallowed
R52 harmful to aquatic organisms
R23
toxic by inhalation
R4
forms very sensitive explosive
metallic compounds
R24
toxic in contact with skin
R53 may cause long term adverse
effects in the aquatic environment
R25
toxic if swallowed
R5
heating may cause an explosion
R26
very toxic by inhalation
R6
explosive with or without contact
with air
R27
very toxic in contact with skin
R28
very toxic if swallowed
R7
may cause fire
R29
contact with water liberates toxic gas
R8
contact with combustible material
may cause fire
R30
can become highly flammable in use
explosive when mixed with
combustible material
R31
contact with acids liberates toxic gas
R32
contact with acids liberates
very toxic gas
R33
danger of cumulative effects
R34
causes burns
R35
causes severe burns
R36
irritating to the eyes
R9
R10 flammable
R11 highly flammable
R12 extremely flammable
R14 reacts violently with water
R15 contact with water liberates
extremely flammable gases
R16 explosive when mixed with
oxidising substances
R17 spontaneously flammable in air
R18 in use may form
flammable / explosive
vapour-air mixture
R19 may form explosive peroxides
R37
irritating to the Respiratory system
R38
irritating to the skin
R39
danger of very serious
irreversible effects
R40
limited evidence of carcinogenic effects
R41
risk of serious damage to eyes
R42
may cause sensitisation by inhalation
R43
may cause sensitisation by
skin contact
R44
risk of explosion if heated
under confinement
R45
may cause cancer
R46
may cause heritable genetic damage
R48
danger of serious damage to health
by prolonged exposure
R49
may cause cancer by inhalation
R60
may impair fertility
R61
may cause harm to the unborn child
R62
possible risk of impaired fertility
R63
possible risk of harm to the unborn
child
R64
may cause harm to breast-fed babies
R65
harmful: may cause lung damage
if swallowed
R66
repeated exposure may cause
skin dryness or cracking
R67
vapours may cause drowsiness
or dizziness
R68
possible risk of irreversible effects
(Numbers 13 & 47 are currently unused.)
R54 toxic to flora
R55 toxic to fauna
R56 toxic to soil organisms
R57 toxic to bees
R58 may cause long term adverse
effects in the environment
R59 dangerous for the ozone layer
© CLEAPSS 2009
Section 7 - Page 45
Chemicals
Flammable chemicals
The classification of flammability of a chemical (usually organic liquids) depends largely on its flash
point (as in table 7.15), although this category now includes solid substances “which become hot and
finally catch fire in contact with air…” or “which, in contact with water or damp air, evolve highlyflammable gases in dangerous quantities”. Examples of these solids would include phosphorus and
sodium. Knowledge of this hazard is important when considering storage or disposal.
Flash point
The flash point is the minimum temperature at which the vapour of the chemical could catch fire just
above the surface of the liquid should there be a source of ignition and sufficient oxygen present. Table
7.8 shows how the hazard is related to flash point. A list of flash points is given in section 20.64 of the
Handbook and, for individual chemicals, they are also published in Hazcards.
Table 7.8
The relationship between flash point and the flammability hazard
Hazard
Flash point
Extremely flammable R12
F
Highly flammable R11
Less than 0 °C and These are very dangerous as ignition can occur
a boiling point of
over large distances between the liquid and the
flame, etc. Storage code FL. Ethoxyethane is a
less than 35 °C.
common example.
Below 21 °C.
Many organic chemicals (eg, ethanol, propanone)
come within this category. The fire hazard symbol
is still displayed and the storage code is still FL.
Between
21 °C and 55 °C.
Should the flammables cupboard be full (ie,
contains more than 50 litres), these chemicals
could be stored with general organic chemicals.
Examples include phenylethene (styrene) and
phenylethanone (acetophenone).
F
Flammable R10
No warning symbol
Comments
Health hazards
Substances or preparations classified as presenting health hazards can cause chronic (long term) or
acute (immediate) damage to health or even death, when inhaled, swallowed or absorbed via the skin.
Chemicals that may destroy living tissue (ie, corrosives) also fall into this category.
C
Several corrosive chemicals are in regular use in schools and all present a serious
danger to the skin and eyes as the results are irreversible. Eye protection and
gloves are essential in their handling. Animal skins are used to assess the extent
of the hazard. If the skin is destroyed within 3 minutes then the substance is said to
“cause severe burns” (R35). If destruction of the skin tissue occurs in a time
between 3 minutes and 4 hours, it is said to “cause burns” (R34). The CORROSIVE
sign is assigned to any chemical with a R34 or R35 risk phrase.
Chemicals
Section 7 - Page 46
© CLEAPSS 2009
Chemicals which may inflame living tissue
H
Inflammation occurs as a result of the body’s defences coping with an invading
harmful substance. Thus the skin might go red, the eyes might water or coughing
and sneezing may start. Chemicals that can cause inflammation of the skin (R38),
eye irritation (R36) or respiratory irritation (R37) are assigned the IRRITANT
symbol. These effects should be reversible if the correct treatment is followed.
However, irritant chemicals should be handled with care, wearing eye protection
and possibly using gloves. Individuals who are prone to dermatitis or skin allergies
will certainly need to use them. Similarly, those with asthma or other bronchial
conditions should be particularly careful of chemicals that are irritant to the
respiratory system.
Chemicals which may be lethal
T
Table 7.9
Category
Very toxic
T
Toxic
T
Harmful
H
Volunteers are reluctant to come forward to test the toxicity of chemicals, so
published results rely mainly on animal studies. The hazard is classified on the
basis of LD50 (d for dose) or LC50 (c for concentration) values. This is a
statistically-calculated concentration or dose which causes death in 50% of a
population of animals which is usually either rat or rabbit. Table 7.16 shows how
these results are interpreted.
How chemicals are classified according to acute toxicity
Limits if swallowed
Limits in contact
with the skin
Limits by inhalation
of gases
Limits by inhalation
of aerosols or
particulates
LD50 oral,
rat ≤ 25 mg kg-1
(R28)
LD50 dermal,
rat or rabbit
≤ 50 mg kg-1 (R27)
LC50 inhalation,
rat ≤ 0.5 mg litre-1
over 4 hr (R26)
LC50 inhalation,
rat ≤ 0.25 mg litre-1
over 4 hr (R26)
25 < LD50 oral,
rat ≤ 200 mg kg-1
(R25)
50 < LD50 dermal,
rat ≤ 400 mg kg-1
(R24)
0.5 < LC50
inhalation,
rat ≤ 2 mg litre-1
over 4 hr (R23)
0.25 < LC50
inhalation,
rat ≤ 1 mg litre-1
over 4 hr (R23)
200 < LD50 oral,
rat ≤ 2000 mg kg-1
(R22)
400 < LD50 dermal,
rat ≤ 2000 mg kg-1
(R21)
2 < LC50 inhalation,
rat ≤ 2 0 mg litre-1
over 4 hr (R20)
1 < LC50 inhalation,
rat ≤ 5 mg litre-1
over 4 hr (R20)
Extrapolating these values to humans is difficult and often based on experience (accidents and
murders!). But for human adults of average mass, it can be estimated that less than 2 g of a very toxic
substance could cause death. Between 2 and 15 g would be deemed TOXIC and between 15 and
125 g would be rated HARMFUL. These values are affected by age and size so these values would be
reduced for children. CLEAPSS knows of a girl who was killed by drinking saturated copper sulfate
solution, which is only rated HARMFUL! However, she drank a much larger quantity than would usually
be available in a school situation.
© CLEAPSS 2009
Section 7 - Page 47
Chemicals
Chemicals which act as sensitisers
Many people are allergic to chemicals (eg, nickel in cheap jewellery), pollen or other fine particulates
emanating from animals, car exhausts or dusts. The allergy may result in a rash on the skin, the eyes
may stream or there may be an increase in catarrh (as in ‘hay fever’).
H
In some cases people can become ‘sensitised’. This term is used to describe that
situation in which the allergic reaction is produced by a very low concentration of the
substance. It is believed that previous exposure to the substance, which has often
been over a long period but may be a single incident, has conditioned the body’s
defence mechanism to react to even a very small amount of that substance. In the
most-serious cases a minute trace of the allergen triggers an extreme
immunological response named ‘anaphylaxis’, as in some reactions to peanuts or
bee venom. If there is evidence that a substance or preparation causes sensitisation
in humans at a significant frequency, then it is labelled either HARMFUL (by
inhalation) or IRRITANT (skin contact) on the bottle, with risk phrases R42 and R43.
Chemicals which act as carcinogens
A carcinogen is a chemical that can induce cancer. Some chemicals are now known to be carcinogenic
to humans and many more are suspected of having this property. This is naturally an emotive subject
and it is littered with rumours. Results from different testing laboratories all over the world often conflict,
so CLEAPSS relies on the information provided by the Health & Safety Executive. Carcinogenicity
poses problems that are quite different from acute toxic effects. First, there is usually a long period after
exposure before the cancer appears and secondly, there is the fear that carcinogens may be effective
at levels that do not produce any immediate toxic effects. In industry, large amounts of substances are
used repeatedly, whereas in school laboratories, substances are used in small amounts and only
infrequently. Those substances that cause cancer in lengthy and high-level industrial exposure are
most unlikely to present a threat to a careful laboratory worker using sensible precautions to control the
risk from any toxic effects. Known, potent human carcinogens are rightly excluded from school use.
Assuming sensible laboratory technique is used, there is little need to worry about carcinogenic
hazards in school science. Most relevant chemicals are only used a few times in a year so any one
person will receive minimal exposure.
Carcinogens are divided into three categories depending on the information available about them.
However, it often happens that a substance merits the classification TOXIC because of its chemical
effects while the carcinogenicity only merits HARMFUL.
Chemicals
Category 1
carcinogens:
T
Section 7 - Page 48
© CLEAPSS 2009
These are the known human carcinogens. Chemicals in this category are subject to
strict legal controls1 that effectively ban some of them from schools. Risk numbers
associated with the hazard are either R45 (may cause cancer) or R49 (may cause
cancer by inhalation). The category includes benzene (R45) and any preparation
containing more than 0.1% benzene, ie, crude oil and petrol. Other materials in this
category which may be found in schools are asbestos (R45), zinc chromate (R45),
nickel oxide (R49) and chromium(VI) oxide (R45).
Asbestos
It is extremely unlikely that the current strict guidelines for asbestos fibres in the air
could be exceeded through laboratory use and the most dangerous form of
asbestos (‘blue asbestos’ or crocidolite) is never found in laboratory apparatus.
Asbestos products were not used in school equipment after 1974. Heatproof mats
bought since then will not contain asbestos although they might look like it.
Benzene
Benzene may no longer be used in education as a solvent, as a chemical reagent or
even as a minor constituent of genuine crude oil or in petrol bought from a pump.
Chromium(VI)
oxide
This was used with concentrated sulfuric(VI) acid to form a solution (chromic acid)
which removed organic stains from glass. It should not be used.
Nickel(II) oxide
This may be found in a pottery department as a glaze.
Zinc
chromate(VI)
Zinc chromate(VI) is prepared by a precipitation reaction between a zinc salt and
potassium chromate(VI) solution. This may be done in schools; however, the solid is
best not isolated and dried but immediately flushed way.
Other
recognised
carcinogens
AM 3/70 (originally issued by the DES) recommends very strongly that certain
chemicals are not stored or used in schools. This recommendation is widely
regarded as a ban and many of these chemicals are actually banned in industry.
The chemicals listed are: naphthalen-1-amine (α-naphthylamine)2 naphthalen-2amine (β-naphthylamine) nitrosoamines (see below) nitrosophenols
nitronaphthalenes chloroethene (vinyl chloride) Biphenyl derivatives with at least
one nitro and/or primary amino group including those with further substitution by
halogeno, methyl or methoxy groups. Possible examples include: biphenyl-4,4'diamine (benzidine), 4-aminobiphenyl (xenylamine), 3,3'-dimethylbiphenyl-4,4'diamine (o-tolidine), 3,3'-dimethoxybiphenyl-4,4'-diamine (o-dianisidine).
1
Control of Substances Hazardous to Health Regulations.
2
This chemical is no longer considered a carcinogen although the ban still applies. Many years ago, supplies of this
amine were heavily contaminated with the carcinogenic isomer which is no longer the case.
© CLEAPSS 2009
Category 2
carcinogens:
T
Section 7 - Page 49
Chemicals
These substances should be regarded as if they were carcinogenic to humans
because although there is no direct evidence, long-term animal studies and other
information implies that there is a link. Chemicals in this category include acrylamide
(R45), cadmium chloride (R45), calcium chromate(vi) (R45), 1,2-dibromoethane
(R45), 1,2-dichloroethane (R45), hydrazinium salts (R45), 2-nitronaphthalene (R45),
potassium bromate (R45), strontium chromate (R45) and beryllium and its
compounds (R49).
Acrylamide
Polyacrylamide gels used for DNA electrophoresis are low hazard and not
carcinogens.
1,2-dibromoethane, etc
1,2-dibromoethane and 1,2-dichloroethane are very volatile and exposure is not
easy to control. They were used in making thiokol rubber in which they were heated.
It is not advisable to carry out these experiments now as the resulting rubber
contains much unreacted monomer.
Potassium
bromate
Potassium bromate is only toxic if swallowed and so there should be no problem in
still making up and using 0.01 M solutions in titration experiments. When treated
with an excess of bromide ion and acid, it provides bromine water of known
concentration.
Category 3
carcinogens:
This category lists substances which cause concern but as yet there is no direct
evidence to link them to human cancers. Tumours have normally been found when
the chemical has been given to some mammals in large doses. To be on the safe
side, they are given a R40 warning (‘limited evidence of carcinogenic effects’).
There continues to be close monitoring of these substances by the Health and
Safety Executive and, if new information comes to light, it will be relayed in the
CLEAPSS Bulletin.
H
Chemicals which act as mutagens
A mutagen is a substance or agent that causes an increase in the rate of change in genes. These
mutations (changes) can be transferred to new cells as the cell reproduces, sometimes leading to
defective cells or cancer. Ethidium bromide and acrylamide are mutagens. Mutagens, like carcinogens,
are divided into three classes according to the information available on their properties and could carry
either TOXIC or HARMFUL symbols and risk phrases R46 or R68.
Chemicals which are toxic to reproduction (once called teratogens)
Some chemicals affect human fertility while others can pass across the placenta wall and affect the
development of the unborn child. Both are ‘toxic to reproduction’, are divided into three classes, and
may carry either TOXIC or HARMFUL symbols and risk phrases R60 to 63. CLEAPSS has produced
Guidance Leaflet PS13 (New & Expectant Mothers Taking Part In School Science). Carbon monoxide
and all lead salts affect development and are placed in class 1. This is yet another reason why the
electrolysis of lead bromide should be carried out in a fume cupboard and, indeed, why care should be
taken during the heating of all lead compounds. Lead salts are also thought to affect human fertility but
are placed only in class 3 for this hazard because the evidence that this can happen is from some
animal studies only.
Chemicals
Section 7 - Page 50
© CLEAPSS 2009
Environmental hazards
Dangerous for the
Environment:
N
Chemicals which are “dangerous for the environment” is the most recent hazard
classification and the number of substances given risk numbers R50 to R59 will
increase as more evidence comes to light. 1,1,1-trichloroethane and
tetrachloromethane are examples of chemicals responsible for depleting the ozone
layer and fall into this category. They are no longer available; see guide L195,
Safer Chemicals, Safer Reactions. Existing stocks should not be used for
‘diffusive purposes’.
Future hazard classifications
CLEAPSS reviews Health & Safety Executive publications, journals, etc, regularly to see if any
substances previously thought to be safe for school use present a significant carcinogenic risk. In June
2007, a European Union (EU) regulation came into force concerning the Registration, Evaluation,
Authorisation and restriction of Chemicals - REACH. The main aims of REACH are to improve the
quality and amount of information we have about the chemicals that we use and to improve the
protection of human health and the environment. This will affect Material Safety Data Sheets.
At some stage in the future, a number of chemicals may become difficult to obtain. This may be for
economic reasons or because a small number of certain chemicals, those categorised as being
’substances of very high concern’, will become subject to restrictions or their use will require
authorisation. This scenario is still some way off, there are many thousands of chemicals to be
processed and the REACH process is likely to be very slow. Up to the end of 2009, this has not
affected the chemicals used in schools. We will keep you fully informed about REACH with articles in
the Bulletin and updates on our web site.
Finally, the United Nations has initiated a “Globally Harmonised System of Classification and Labelling
of Chemicals (GHS)”. This will be recognised by all the countries in the world. Should you ever see the
pictogram below, you will know that GHS is here.
© CLEAPSS 2010
7.9
Section 7 - Page 51
Chemicals
Control of airborne chemical exposure
(See also CLEAPSS guidance leaflet PS15.)
The control of airborne chemical exposure significantly influences the scale of practical work that can
be carried out in an open laboratory, rather than a fume cupboard.
The Control of Substances Hazardous to Health (COSHH) Regulations require risks to be assessed
when using or making any substance that:
•
is assigned a Work Exposure Limit (WEL),
•
produces a dust or fume at significant concentration.
The sections that follow provide information about chemicals which are assigned work exposure limits
which form part of the basis for the model risk assessments in Hazcards and in writing CLEAPSS
supplementary and special risk assessments.
Workplace Exposure Limits (WEL)
WELs are given in the HSE publication Guidance Note EH40. Some hazardous chemicals are not listed
in EH40 because the HSE has been unable to establish, to its own satisfaction, a safe exposure limit,
for example sulfur dioxide and nitrogen dioxide. The absence of a chemical from EH40 cannot
therefore be taken to imply that the chemical is considered safe. WELs have replaced Maximum
Exposure Limits (MELs) and Occupational Exposure Standards (OESs). The limits are updated
regularly in the light of developing information and research. Future changes that affect work in school
science will be published in the CLEAPSS Bulletin and ultimately in new editions of Hazcards.
The revised list from EH40 can be found at www.hse.gov.uk/coshh/table1.pdf.
Until 2005 it had been normal for HSE to publish a new paper edition of EH40, or at least an
amendment, each year. However, with increasing use of its web site the HSE has not recently
published a revised hard copy edition, or amendment. It has updated the table on its web site in both
2006 and 2007 but not since.
A WEL is the maximum concentration to which employees may be exposed by inhalation (averaged
over a certain time span). The value is not a distinction between levels which are unsafe or safe, and,
in practice, exposure should be kept well below any relevant WEL value. If the substance is a class 1 or
2 carcinogen or a sensitiser, the level of exposure should be reduced to substantially below the WEL,
at a level that is still reasonably practicable.
Values for WELs are found in all the relevant Hazcards; an example from Hazcard 43A is shown below.
There are two values provided, a long-term exposure limit (LTEL: 8 hours) and short-term exposure
limit (STEL: 15 minutes) each of which is an average value over the specific period of time. This is
known as a Time-Weighted Average (TWA). Within each time period the actual amount of airborne
contaminant may vary but it must not exceed the average over the period. Thus, for example, a gas
may momentarily exceed its WEL but be quickly removed by ventilation so that over the period of
15 minutes the average is below the STEL.
Chemicals
Section 7 - Page 52
© CLEAPSS 2010
Where EH40 does not specifically define a STEL for a particular chemical, it recommends that a figure
of three times the LTEL be used as a guideline. The absence of a WEL value does not imply that a
substance is safe. Should more information be required, contact CLEAPSS. Employers may set their
own WELs for non-listed chemicals, and CLEAPSS has done this, on behalf of its members, for sulfur
dioxide and nitrogen dioxide, using European data and practice.
Types of contaminants and units used in WELs
Airborne contaminants include gases, vapours, and particles, such as fumes, dusts and fibres. Fumes
are airborne particles, including solid particles, generated by chemical reactions or condensed from the
gaseous state. For example, ammonium chloride can form a fume on heating and where ammonia and
hydrogen chloride gases combined.
Concentrations of airborne particles are quoted in mg m-3. Concentrations of gases and vapours are
also quoted in ppm (parts per million) as well as mg m-3. Hazcards provides values in mg m-3 but many
books and measuring instruments use ppm as the unit.
The equation below shows the relationship between the two units.
WEL in ppm =
WEL (mg m −3 ) × 24.05526
molar mass(g mol −1 )
Fibres of man-made mineral fibre (MMMF) are defined as particles with a length greater than 5 µm, a
diameter of less than 3 µm and a ratio of length to diameter greater than three to one. It is most unlikely
that levels for such fibres will be exceeded in a school laboratory. In correspondence with CLEAPSS’
sister organisation in Scotland, SSERC, the HSE Employment Medical Advisory Service has advised
that levels of MMMF in schools would be very low and added that in their experience:
(i)
the amounts were very small and, if carefully handled, then the fibre count would almost certainly
be so low as to be immeasurable;
(ii)
the time of exposure was very short and when averaged over the 8-hour day the Time-Weighted
Average concentration would be even lower.”
Relevance to schools
It is worth repeating that the control of airborne chemical exposure is an important consideration on
how practical work can be carried out. It provides a very persuasive argument for a move towards
using smaller amounts of chemicals as in microscale chemistry.
The values given in WELs, based upon years of research and experience in the work environment, are
designed essentially for industrial activities. Applying the values for work in schools is not easy but the
following guidance has helped CLEAPSS to produce model risk assessments on Hazcards.
A school laboratory of over 80 m2 has a typical volume of 240 m3. Older rooms may be larger
whereas prep and store rooms are much smaller and hence airborne concentrations could be
larger.
If 1 g (ie, 338 cm3) of chlorine gas is released in a 240 m3 room, the concentration of the gas is
1000 / 240 or 4.2 mg m-3. (This is the above the STEL of 1.5 mg m-3.) This is why work with gas
jars of chlorine should always take place in fume cupboards.
© CLEAPSS 2010
Section 7 - Page 53
Chemicals
The value of a WEL represents the contaminant evenly distributed throughout a room that has no
ventilation. Naturally, a contaminant that has just been released will be more concentrated near the
position of release than in areas further away, although diffusion may be quite rapid. Despite the
obvious unevenness of concentrations, the calculation above is still useful for preparing an assessment
on potential airborne concentrations of contaminants.
Chemical storage rooms may be subject to a gradual leakage of gas and vapour from stored
chemicals. In general, staff do not stay in these rooms for long periods unless they are dispensing or
stock-taking so WELs are very unlikely to be approached or exceeded. However, should the chemicals
be kept in a prep room or laboratory, the 8-hour LTEL may need to be considered and a special risk
assessment may be required.
If chemical reactions, dispensing or accidental spills involve the release of gases or vapours, STEL
values are used to provide guidance.
Pupils with a lower body mass and high metabolism are more susceptible to chemicals in the
atmosphere than adults. Therefore it would not be sensible to expose pupils to levels close to the WEL.
A worked example of potential exposure concentrations
15 groups of pupils, (in an open lab of volume 240 m3) are to make 0.2 g of iron(II) sulfide [Mr(FeS) is
88 g mol-1] which they react with acid to release hydrogen sulfide [Mr(H2S) is 34 g mol-1]. This takes
10 minutes. Will the WEL for hydrogen sulfide be exceeded? (14 mg m-3 for the 15 minute TWA.)
1 mole of iron(II) sulfide produces 1 mole of hydrogen sulfide. So 88 g of iron sulfide produces 34 g of
hydrogen sulfide, hence 0.2 g of FeS produces 0.077 g or 77 mg of H2S.
The average concentration of H2S will be 77 × 15 / 240 or 4.8 mg m-3.
The value averaged over the 15 minute-TWA is 4.8 × 10 / 15 or 3.2 mg m-3 - well below the limit.
The calculation demonstrates that this experiment could be done in an open laboratory. In practice,
this procedure might be limited to a demonstration because the revolting odour of hydrogen sulfide
can be detected at levels around 0.01 mg m-3. In addition, those working in adjacent laboratories
would object to the smell.
Odour levels
Sometimes, the concentration of a chemical in the laboratory atmosphere can be estimated by its
odour. Values for the concentration at which some substances can be just detected are given in HSE
Guidance Note EH64, and may also appear on some Safety Data Sheets. We have reproduced this
data in Table 7.10. However, reliance on odour thresholds can be unreliable because:
•
some materials can cause fatigue in the olfactory nerves and destroy the sense of smell (eg,
hydrogen sulphide);
•
the level at which odour is detected by the nose varies from one person to another;
•
some materials may be present in excess of their WELs but undetectable by smell (fortunately,
this is very rare with school chemicals);
•
published values vary from one source to another;
•
workers may become tolerant to a commonly-occurring odour.
Despite these issues, it is possible to use odour as a guide that should warn you to take action.
Chemicals
Section 7 - Page 54
Table 7.10
Name
1-
© CLEAPSS 2010
Odour levels
3
WEL (mg/m )
Odour
level
3
(mg/m )
Name
3
WEL (mg/m )
Odour
level
3
(mg/m )
aminobutane
15 (LTEL), 45 (STEL)
5.5
hydrogen chloride
2 (LTEL), 8 (STEL)
1.2
ammonia gas
18 (LTEL), 25 (STEL)
3.7
hydrogen sulfide
7 (LTEL), 14 (STEL)
0.01
benzene
3.3 (LTEL)
39
methanal solution
2.5 (LTEL), 2.5 (STEL)
1.0
bromine
0.7 (LTEL), 1.3 (STEL)
0.34
methanoic acid
9.6 (LTEL), 28.8 (STEL)
94
bromoethane
906 (LTEL), 1130 (STEL)
14
methanol
200 (LTEL), 333 (STEL)
133
butan-1-ol
154 (STEL)
2.6
methyl 2-
208 (LTEL), 416 (STEL)
0.35
methylpropenoate
butan-2-ol
308 (LTEL), 462 (STEL)
8.0
methyl ethanoate
616 (LTEL), 770 (STEL)
0.12
butane gas
1450 (LTEL),1810 (STEL)
6510
methyl methanoate
250 (LTEL), 374 (STEL)
12
butanone
600 (LTEL), 899 (STEL)
16
methylamine
13 (LTEL), 39 (STEL)
4.1
methylamine gas
13 (LTEL), 39 (STEL)
4.1
methylbenzene
191 (LTEL), 384 (STEL)
11
(40% solution)
butyl ethanoate
724 (LTEL), 966 (STEL)
1.9
carbon dioxide
9000 (LTEL), 27000 (STEL) 135000
carbon disulfide
32 (LTEL), 96 (STEL) Sk
0.35
3-
methylbutan-1-ol
366 (STEL), 458 (STEL)
0.15
carbon monoxide
35 (LTEL), 232 (STEL)
120000
3-
methylphenol
22 (LTEL)
0.01
72 (LTEL), 143 (STEL)
0.03
chlorine
1.5 (STEL)
0.91
2-
methylprop-3eneoic acid
chlorobenzene
23 (LTEL), 70 (STEL)
3.2
2-
methylpropan-1-ol
154 (LTEL), 231 (STEL)
0.13
cyclo-1,4-oxybutane
150 (LTEL), 300 (STEL)
6.0
2-
methylpropan-2-ol
308 (LTEL), 462 (STEL)
145
cyclohexane
700 (LTEL), 2100 (STEL)
87
naphthalene
10 (LTEL), 30 (STEL)
0.45
cyclohexanol
208 (LTEL), 624 (STEL)
42
nitrobenzene
1(LTEL), 2 (STEL)
0.09
cyclohexanone
41 (LTEL), 82 (STEL)
3.6
nitrogen dioxide
1.9 (LTEL), 1.9 (STEL)
0.71
cyclohexene
1020 (LTEL)
0.61
ozone gas
0.2 (STEL)
0.09
1,4- dichlorobenzene
153 (LTEL), 306 (STEL)
1.1
pentane
1800 (LTEL), 5400 (STEL)
1200
1,2- dichlorobenzene
153 (LTEL), 306 (STEL)
1.8
pentyl ethanoate
270 (LTEL), 541 (STEL)
0.29
1,2- dichloroethane
21 (LTEL), 63 (STEL)
70
phenol
7.7 (LTEL), 23.1 (STEL)
0.12
dichloromethane
350 (LTEL), 1060 (STEL) Sk 883
phenylamine
4 (LTEL), 12 (STEL) Sk
4.3
diethylamine
15 (LTEL), 30 (STEL)
0.57
phenylethene
430 (LTEL), 1080 STEL)
1.4
dimethylamine
2 (LTEL), 6 (STEL)
0.63
phosphine
0.14 (LTEL), 0.28 (STEL)
24
ethanal
37 (LTEL), 92 (STEL)
0.09
propan-1-ol
500 (LTEL), 625 (STEL)
6.5
ethanenitrile
70 (LTEL), 210 (STEL)
290
propan-2-ol
999 (LTEL), 1250 (STEL)
55
ethanoic acid
25 (LTEL), 37 (STEL)
1.2
propanoic acid
31 (LTEL), 46 (STEL)
0.49
ethanoic anhydride
2.5 (LTEL), 10 (STEL)
0.55
propanone
1210 (LTEL), 3630 (STEL)
31
ethanol
1920 (LTEL), 5760 (STEL)
1.6
propyl ethanoate
849 (LTEL), 1060 (STEL)
2.8
ethoxyethane
310 (LTEL), 620 (STEL)
27
pyridine
16 (LTEL), 33 (STEL)
0.56
ethyl ethanoate
681 (LTEL), 1362 (STEL)
14
sulfur dioxide
2.7 (LTEL), 2.7 (STEL)
2.9
ethyl methanoate
308 (LTEL), 462 (STEL)
95
tetrachloroethene
345 (LTEL), 689 (STEL)
883
ethylamine
3.8 (LTEL), 11 (STEL)
1.8
tetrachloromethane
13 (LTEL), 39 (STEL)
615
ethylamine
3.8 (LTEL), 11 (STEL)
1.8
555 (LTEL), 1110 (STEL)
666
hexane
72 (LTEL), 216 (STEL)
465
trichloroethene
550 (LTEL), 820 (STEL)
153
hydrogen bromide
10 (STEL)
6.7
trichloromethane
9.9 (LTEL), 29.7 (STEL) Sk
420
1,1,1 -trichloroethane
Note: in Table 7.10 above, Sk means absorbed through the skin.
© CLEAPSS 2010
Section 7 - Page 55
Chemicals
For odours from:
•
Bromine or trichloromethane, ventilate the room immediately to remove the vapour because the
odour level is well above the WEL. Take steps to prevent further leaks.
•
Ethanoic acid, hexane or phenylamine, take steps to remove the vapour and prevent its
recurrence but, since the level is only just above the WEL STEL, if the exposure is only for a few
minutes, this is less important.
Many other substances used in schools may produce an odour but these are detected by the nose at
levels well below the STEL values. Further evidence of high concentrations of contaminant is
necessary before action becomes essential.
Carbon dioxide has no odour and the WEL is so high that it would appear to prevent few problems.
However, it is a product of human respiration and gas combustion, and unless ventilation is present,
CO2 levels can cause deterioration in pupil performance and an uncomfortable working environment.
See Guidance leaflet PS15 for further details.
Measuring WELs in schools
Electronic measurement is not cheap. CLEAPSS have an electronic mercury sensor should any school
or local authority wish to have mercury levels monitored. There will be a charge for this service.
Chemical methods draw gas through a chemical-filled tube that changes colour. A pump is also
required. Costs of these systems will come to a couple of hundred pounds but if the school carries out
the annual test of its own filter fume cupboard(s), it will have one of these systems.
The Gastec
Dositube
system
a1-envirosciences group
Head Office (UK & Eire)
20 Charles Street,
Luton, Bedfordshire
UK, LU2 0EB
Tel: + 44 (0) 1582 747502
Fax: + 44 (0) 1582 747503
a1-info@a1-envirosciences.co.uk
www.a1-envirosciences.com
Draegar
Tubes for
Long-term
Measuremens
Draeger Safety UK Ltd.
Ullswater Close
Blyth Riverside Business Park
Blyth
Northumberland NE24 4RG
United Kingdom
Tel +44 1670 35 2891
Fax +44 1670 356 266
Chemicals
Section 7 - Page 56
© CLEAPSS 2010
Estimation of exposure levels using chemical equations.
Calculations such as these could be used with post-16 chemistry students to teach and practice the
process of calculations of stochiometric reactions
Example 1
Find the maximum mass of copper(II) nitrate(V)-3-water (Mr:241.5 g mol-1) which could be heated
safely in a laboratory of volume 240 m3 so that the concentration of NO2 (STEL 1.9 mg m-3) is not
exceeded.
2Cu(NO3)2.3H2O(s) → 2CuO(s) + 4NO2(g) + O2(g) + 3H2O(l)
Maximum mass of nitrogen dioxide allowed in the room is 1.9 × 240 or 456 mg.
To produce 456 mg of nitrogen dioxide (0.0104 mol) requires the complete decomposition of 0.052 mol
of copper(II) nitrate(V)-3-water (12.6 g).
•
This means a class of 15 groups would be able to decompose only 0.8 g per group and a teacher
demonstrating the reaction only 12.6 g.
•
The calculation makes no allowance for localised concentrations. Hence the person doing the
experiment will suffer before those further away.
•
The calculation makes no allowance for ventilation or other control.
In general, therefore, heating copper nitrate should be carried out in a fume cupboard, either as a
teacher demonstration or possibly by students as part of a circus of experiments.
Example 2
Will the electrolysis of sodium chloride solution produce an unsafe level of chlorine in the laboratory?
(STEL for chlorine of 1.5 mg m-3.)
A current of 0.05 A is passed through sodium chloride solution for 15 minutes (15 × 60 seconds) by
15 sets of pupils in a 240 m3 room.
Amount of charge is 0.05 ×15 × 60 = 45 Coulombs per group.
A Faraday (96500 C) is the charge carried by one mole of electrons,
For any one group: the amount of electrons carried is 45 ÷ 965000 = 0.00047 mol.
The equation which represents the discharge of the chlorine at the anode is:
2Cl–(aq) - 2e– → Cl2(g)
The amount of chlorine formed per group is 0.00047 × 71 × 0.5 = 0.17 g or 170 mg.
The average concentration in the room would be 170 ÷ 240
= 0.7 mg m-3.
For 15 groups the concentration of chlorine would be 10.5 mg m-3, which is 10 times the STEL.
Therefore:
•
This practical activity should not go ahead in this form since the chlorine level is ten times the
STEL.
•
The level of chlorine could be reduced to about the STEL value by ensuring that students switch
off the electric current once observations have been made (eg, that moist blue litmus is
bleached), ie, after 2 minutes or less.
•
Reducing the time the for the electrolysis to just 1 minute will reduce exposure but even so, those
breathing difficulties may need to take care.
These conclusions and comments are summarised on the Hazcard for sodium salts.
© CLEAPSS 2010
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Appendix 7A Legal issues affecting storage of chemicals
Schools must comply with the few legal requirements that apply to the storage of small amounts of
chemicals. In some cases, there will also be rules made by the employer, which must be followed. Any
requirements made as a consequence of the fire risk assessment must also be followed.
Special stores and cupboards
The common issues raised about chemical storage are to do with the storage of flammable and
corrosive liquids, the potential for flammable and other harmful vapours and the risk of fire. Advice is
often contradictory, and has produced a large number of enquiries to CLEAPSS requesting clarification.
In terms of special stores or cupboards, there is a requirement for fire-resistant storage of highly and
extremely flammable liquids. This could be the store itself, or a special flammables cupboard.
A fire-resisting store
A fire-resisting store is required if there is more than 50 litres of highly flammable material.
External stores are often of prefabricated construction and such units are available with various
degrees of fire resistance. Under DSEAR, the following materials are deemed to be of minimal risk and
do not require to be tested further; concrete, fired clay (brick), ceramics, steel, concrete blocks and
plaster and masonry containing not more than 1% by weight or volume of organic material. Otherwise,
if the building adjoins the school1, the building material will need 60 minutes fire resistance.
Whether internal or external, flammable-liquid stores should be particularly carefully sited, account
being taken of the need to:
•
maintain escape routes in a fire,
•
ensure that, in the interests of safe handling, dangerous chemicals should be kept as near as
possible to the laboratories in which they are most likely to be used,
•
prevent access by vandals, and
•
shade from direct heating by the Sun.
Heating for frost and condensation protection is desirable in external stores (eg, with a thermostat set
to 10 °C) and the cost of this is one of the major arguments against an external site.
Windows should be avoided; they are not permitted on internal walls (ie, walls common to a main
building and an external store) and are not advisable for security reasons on external walls.
One door only is preferable unless the store is very large (for a school) in which case more exits may
be required for fire safety. Doors should open outward. It should not be possible for somebody to be
inadvertently locked inside the store. The entrance to the store should be ramped so that a trolley can
be wheeled in.
Much is made of containment but the catastrophic destruction of all containers in the store is extremely
remote. If the free floor space is 3 m by 2 m and a full 25-litre drum suddenly leaks, then the depth of
the spill is less than 0.5 cm! If the floor slopes slightly to the centre, the spill will collect in an accessible
place (not a drain) and possibly2 dealt with the spill kit that is kept inside the store.
1
Schools are mentioned in DSEAR as a vulnerable audience.
2
Teachers and technicians should not themselves at risk when dealing with the spill of a hazardous chemical.
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Flammables cupboards must conform to data found in Appendix 2
of The Storage Of Flammable Liquids1. Typical examples are shown
in the photograph. Amongst the requirements are at least 30 minute
fire integrity, class 0 surface spread of flame, fastenings that have a
melting point greater than 750 °C and sufficiently durable that any
spillages within the cabinet can be contained and removed without
affecting fire resistance.
A special corrosives cupboard is often suggested for keeping
corrosive chemicals. Not surprisingly, these cupboards corrode,
especially the locks and hinges, (which always disappoints those
who buy them). They are usually made of steel with thick coating of
paint and while they are suitable for unopened bottles of
concentrated acids but once opened corrosive vapours escape and
attack the locks and hinges. Schools can store unopened bottles of
corrosives on a shelf; so we do not recommend these cupboards.
Mechanically-ventilated cupboards are available but are very expensive. However, if you are having a
new ducted fume cupboard installed then many of the manufacturers will put a cupboard underneath
which is connected to the fume cupboard. Even if the fume cupboard is not on and the sash is closed,
the fumes will vent up the flue but obviously, when the fume cupboard is on, the cupboard will be
completely vented of any fumes. Such a vented cupboard is useful for storing corrosives. To ensure
regular ventilation, a time switch can be installed to operate the fume cupboard for a few minutes very
few hours. However, any waste and electrical services below the fume cupboard must be protected
from the corrosive fumes
Ventilation in a chemical store
The Workplace (Health, Safety and Welfare) Regulations 19922 state, in section 6 (1), “Effective and
suitable provision shall be made to ensure that every enclosed workplace is ventilated by a sufficient
quantity of fresh or purified air.”
The Education (School Premises) Regulations 19993 state, in 21 (2), “All teaching accommodation,
…… shall also be capable of being ventilated at a minimum rate of 8 litres of fresh air per second for
each of the usual number of people in those areas when such areas are occupied”.
And in section 21(4) “Adequate measures shall be taken to prevent condensation in, and remove
noxious fumes from, every kitchen and other rooms in which there may be steam or noxious fumes.”
1
HSG51, ISBN 0717614719, HSE Books. Although published under the previous Regulations, this is still the basis of
current advice.
2
Statutory Instrument 1992 No. 3004.
3
Statutory Instrument 1999 No. 2.
© CLEAPSS 2010
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These rules are amplified in guidance in Ventilation In School Buildings, BB1011, which states;
“Chemicals should preferably be stored in a dedicated chemical store room. As these are not occupied
for significant lengths of time, a ventilation rate of 2 ach (air changes per hour) should suffice. Store
rooms with well-sealed fire doors can preclude inward make-up air to replace exhausted air. This
problem may also arise to a lesser extent with modern laboratories and prep rooms with highly sealed
windows. Pathways for make-up air, and the location of intakes in relation to outlets, therefore need to
be considered carefully. It is sometimes possible to fit grilles, even in fire doors.”
It also emphasises original advice from CLEAPSS: “Preparation rooms usually adjoin science labs and
tend to suffer from inadequate ventilation. Often they are used to store chemicals, but regardless of
this, CLEAPSS suggests a ventilation rate of 5 ach should be adequate.”
Electrical fittings, switch gear in the store and assessment of fire risk
There are many reports of electrical switch gear being placed in the chemical store or the prep room
where the flammables cupboard is cited. CLEAPSS is often asked if this is allowed, because of the
possibility of sparks setting off a fire or explosion2. In addition, it is commonly expected that special
electrical fittings will be necessary in a place where flammables are stored. Siting switch gear in a store
should be resisted because it takes up precious wall space.
The requirements for electrical fittings in flammable atmospheres are laid down by British Standard
BS 5345 which defines three categories of risk and divides an area into corresponding ‘zones’.
•
A region where a flammable mixture of vapour and air is normally present is called ‘Zone 0’. It is
difficult to imagine a situation where this would ever occur in schools.
•
A region where a flammable mixture is likely to be present is called ‘Zone 1’. This might occur in
the immediate vicinity of a petrol-driven lawn mower and a container of fuel in a store.
•
A region where a flammable mixture is unlikely to be or is infrequently present is called ‘Zone 2’.
A Zone 2 region usually surrounds a Zone 1 (or Zone 0) region.
A laboratory where flammable liquids are used might contain a small Zone 2 region but the whole room
is not automatically regarded as Zone 2. Similar conditions are to be expected in a prep room where
flammable liquids are occasionally dispensed or used.
A store only contains a hazardous region when it is also used for dispensing: an activity that is more
likely in an external store than in an internal one. Whether this is Zone 1 or Zone 2 or both depends on
the liquids dispensed, the frequency with which this is done and whether or not there is forced
ventilation. If conditions are judged to be Zone 2 over the dispensing bench, this does not imply that the
whole store reaches that level of hazard and standard lighting fittings and fans could be acceptable.
1
DfES, ISBN 0112711642. Download from
www.teachernet.gov.uk/management/resourcesfinanceandbuilding/schoolbuildings/environ/iaq/.
2
To our knowledge, this has never happened in a school. Fires are mostly caused by electrical problems in electrical
wiring faults or arson. In science departments that have burnt down, the only recognisable structure left is the
flammable cabinet with the containers inside intact! (Which is as it should be.)
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Where fittings are to be located in a Zoned area, they must meet the requirements contained in
BS 5345. Electrical equipment for a Zone 2 area now requires certification to standard ‘N’ or above as
specified in BS 6941 (1988) and it requires inspection at two-yearly intervals. Clearly, it is much simpler
to avoid the hazard:
•
by dispensing in the largest, well-ventilated area available;
•
by locating switches outside the store if they might otherwise be in a Zone 2 area;
•
by resisting any attempt to combine the chemical storage with that used by grounds staff1.
Assessment of fire risk from flammable vapours in a chemical store
The following points will enable you to assess the risk from flammable vapour levels and therefore the
need for spark-proof electrical fittings.
•
Will any highly-flammable liquids be poured from one container to another in the store?
If the answer is ‘No’, then the risk is minimal and no special precautions are required.
•
If the answer is ‘Yes’, what volume will be transferred during any 15-minute period?
If the answer is ‘100 ml or less’, then the risk is minimal and no special precautions are required.
•
If the answer is ‘More than 100 ml’ then it is necessary to estimate the ventilation rate of the store.
This can be done using an air-flow meter (as used for testing fume cupboards) next to the air brick
or fan extract. The product of the flow rate and the area of the aperture gives the volume flow rate
which can be converted to m3 h-1 and divided by the room volume to obtain the number of air
changes per hour. (See example below.)
•
If there are 5 air changes per hour, then the risk is minimal and no special precautions are required.
If there are only 3 air changes per hour, then there could be a Zone 2 region over the dispensing
bench, extending up to 1 m from the filled container in every direction. If the ventilation is minimal,
there could be a Zone 1 region within 50 cm of the container with a Zone 2 region around that up to
1.5 m from the container. If the light fitting lies in this zone, it should be to BS 6941 standard N. The
light switch would be best located outside the store.
Example calculation
Suppose the flow rate through an air brick is 0.4 m s-1 (measured with an air-flow meter used for fumecupboard testing) and the air brick is 0.14 m by 0.22 m of which half the area is actually open holes.
The store is 1.5 m wide, 3 m long and the ceiling is 3 m from the floor.
The volume flow rate is given by…
0.14 × 0.22 × 0.5 × 0.4 m3 s-1
= 6.1 × 10-3 m3 s-1 (m3 per second) or 6.1 × 10-3 × 3600 m3 h-1 (m3 per hour)
= 22 m3 h-1
The volume of the store is then given by = 1.5 × 3 × 3 m3 =13.5 m3
So the number of air changes per hour
22
= 13.5 = 1.6
This number of air changes per hour is quite low so there may be a build-up of highly flammable vapour
should dispensing of highly flammable liquids be carried out. Consequently, this store is not suitable for
dispensing highly-flammable liquids unless the light fitting is to BS 6941 standard N.
1
See also section 8.8, Refrigerators and freezers.
© CLEAPSS 2010
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Appendix 7B Model risk assessment for chemical storage
CLEAPSS Helpline enquiries often begin along the lines of ‘we have been asked for a COSHH
assessment for all the chemicals in the store’ or ‘we have been asked for a risk assessment for the
chemical store’.
As long as storage is well considered, well organised and secure there are almost no risks from the
chemicals. Therefore, to help science departments simply and sensibly complete a risk assessment we
have constructed a model risk assessment of the storage of chemicals. This establishes and confirms
that certain procedures are followed. Once completed the document would be useful to help keep
others in the school, not necessarily in the science department, informed.
Much detail will depend on the situation of your school. Table 7.10 is a model for a chemical storage
risk assessment, but it will probably need tailoring to your situation. A customisable document for you to
modify can be found in the customisable documents section in the Secondary Resource part of the
CLEAPSS web site and the Science Publications CD-ROM.
Table 7.10 Model Risk Assessment for the Storage of Chemicals
Issues to be dealt with
Planned practice and procedures
Managing the store
Day to day running of the chemical store is managed by …………
who will liase with ………… the relevant line manager.
Staff training
The person managing the chemical store will read section 7.3 of the
Handbook. Science technicians and science teachers, new to the
school, will be shown how chemicals are, stored in the school and
requisitioned and delivered for use in experiments.
Security of the store
The storeroom will be locked when not occupied by authorised
personnel. The key is kept ………… .
Where chemicals are stored
The chemicals are stored in ………… .
Which chemicals are stored
The person managing the store should update the inventory of the
chemicals once a year.
Communication (Who needs to
know what is stored?)
The science teachers and technicians are required to know where the
inventory is. The finance office should also have a list and if possible, a
list should be kept in a building not attached to the science department
in case of fire. The responsibility for this communication rests with
………… .
Deliveries of chemicals to the
school / store
When chemicals arrive at the school office, the technician will be
immediately called. If no technician or science teacher is available, the
chemical will be put in a secure room. Office staff must be given advice
on dealing with this situation.
Moving chemicals in and in and
out of the store
The use of bottle carriers and trolleys must be adhered to. See
department safety policy.
Clear identification of hazardous
properties
All bottles, whether stock or waste, are labelled with their name, hazard
symbol and date of purchase (if relevant).
Location of hazard information
Hazard data sheets are kept in ………… .
However, these sheets are more relevant to bulk storage of
chemicals Hazcards will be more suitable for school use and are
kept in ………… .
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© CLEAPSS 2010
Table 7.10 Model Risk Assessment for the Storage of Chemicals (continued)
Issues to be dealt with
Planned practice and procedures
Spills
A spillage kit will be provided in the store room(s).
Determining quantities to be
stored
A relevant risk assessment will be undertaken before any purchase of a
large volume or mass of dangerous substances.
Dispensing chemicals
To ensure there is no chance of a dangerous or explosive atmosphere,
no dispensing of chemicals will take place in the chemical store. If,
under exceptional circumstances this cannot be avoided, a suitable risk
assessment should be made by ………… .
Storing gas cylinders
Gas cylinders will be kept securely in ………… .
Conditions in the store
The temperature of the store will be monitored to ensure that it does not
fall below 0 °C or regularly exceed 28 °C. If the latter temperature is
exceeded, the bottles in the flammable store will be opened and
resealed to relieve a build up of pressure within the bottle. In either
case, the situation will be reported to a member of the school senior
management.
Ensure good ventilation in room(s) where flammable liquids are
stored by ………… . (It is not necessary for highly-flammable liquids
cupboards to be ventilated.)
Clean vents and check the rate of air extraction regularly (at least
once per year and possibly more frequently).
Routine inspection and
maintenance
The lids of all bottles will be checked, by whoever is moving them, for
tightness, whenever they are returned to the store.
The person responsible for the store will periodically (termly?) check
the security of all container for leaks, etc.
Metallic surfaces will be checked termly for corrosion.
Ventilation systems will be checked weekly to ensure they are
working.
Fire precautions
The store has been checked for the possibility that flammable vapour
could be ignited by electrical sparks and necessary actions taken
(see Appendix A)
Suitable hazard signs are in place on the door and on containers in
the store
In the event of a fire in the school, the rooms containing chemicals
will be made secure.
In the event of a fire in or very close to a chemical store, evacuate
the building.
Updating the risk assessment
This Risk Assessment will be reviewed periodically and in any event
when significant changes are made to the quantity or range of chemicals
stored.
© CLEAPSS 2010
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Appendix 7C Waste disposal, the law and environmental
issues
There is a range of legislation covering the disposal of waste (ie, mostly solids) and effluent (ie, via the
drains) but much of it is concerned with the licensing of sites, etc. There have been many recent
changes and more are planned.
In all consideration of waste disposal it is important to distinguish between waste which is collected
and taken away (usually solids and non-aqueous liquids) by any waste removal organisation, and
effluent which is disposed of via the drains (as solutions in water). Most legislation applies to only
one type of waste.
The legislation that drives all the regulations applicable to waste is the Environmental Protection Act
1990. This is a fundamental Act that has given rise to a whole series of Regulations. It introduces an
explicit duty of care to all those handling waste, including those producing it. There is a duty of care on
the disposer to ensure that waste does not harm future handlers. (Radioactive waste is not at present
covered by this Act.)
Recent European legislation on waste is implemented in the UK by The Hazardous Waste Regulations
2005 (as amended 2009) and The List of Wastes Regulations 2005. An important detail of these
Regulations is that, school waste is no longer regarded as domestic (or household) waste and this has
implications for how it must be dealt with. It confirms that how we might dispose of material at home is
not necessarily what we can do at school. (In fact, waste from school laboratories has not been
regarded as domestic waste since 1996.)
In general, The Environment Agency needs to know if any organisation produces waste. However,
schools and colleges in England are exempt from notification if they produce less than 500 kg of
hazardous waste in any one year but the limit still remains at 200 Kg in Wales. Hazardous waste may
include many things in addition to hazardous chemicals, for example, fluorescent light tubes, computers
and refrigerators. Thus, although it is unlikely that the science department will produce sufficient waste
to require notification, the school as a whole may well do so. The Environment Agency must be notified
before the limit is reached.
Schools may produce substances proscribed by these regulations but will do so in such tiny quantities
as to not require any particular action.
Hazardous waste collection
Hazardous waste must be collected by a Registered Waste Carrier.
Waste chemicals are considered hazardous if they are describes as hazardous in the List of Wastes
Regulations. Mixtures are considered hazardous only if the concentration of hazardous components
exceeds a threshold (which varies according to the nature of the hazard). It is illegal to mix hazardous
waste deliberately with an inert dilutant (eg, sand) to reduce its concentration to below the threshold.
On the other hand, if a mixture is produced accidentally, eg, as a result of clearing up a spill, and if the
final concentration is below the threshold, then the mixture can be disposed of in the normal refuse,
without using a Registered Waste Carrier.
Hazardous waste being collected will be listed on a Consignment Note, a copy of which will be sent by
the Registered Waste Carrier (or one exempt from registration) to the Environment agency. Another
copy will be given to the school, which must keep this securely for at least three years. It would be
prudent to make further copies for the school office and the relevant department. Unfortunately, there
are some ‘cowboys’ around in the waste disposal business. Schools should ask to see the evidence of
the carrier’s registration (or exemption). Waste producers (including schools) have a legal duty to check
that any Waste Carrier they use is registered (or is exempt).
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© CLEAPSS 2010
All schools will need to use the services of a Registered Waste Carrier from time to time and this must
be budgeted for. As most of the hazardous waste generated in schools will not originate in the science
department, it would seem unreasonable for the costs to be charged to the department.
CLEAPSS produces and maintains a list of Registered Waste Carriers; see PS5. It is not a list of
‘approved’ companies but we do know that they have worked with schools. The local Yellow Pages will
probably suggest further names but be warned that local does not necessarily mean cheaper.
SIC code. Some schools have been asked by waste-disposal contractors for their SIC code. The
current UK Standard Industrial Classification (SIC) of Economic Activities 2003 lists general secondary
education as code 85.31. The codes for technical and vocational secondary education are 80.22 and
85.32 respectively; these would apply to most FE colleges and perhaps some sixth-form colleges.
Disposal of waste in the refuse collection
It is now illegal to dispose of any chemical classed as hazardous in the refuse collection. Modern
bottles will normally have a hazard warning label but older ones may not. You can find hazard
information on Hazcards, the electronic document E233 and in section 1.3 of the Handbook (Chemicals
Hazard and Storage Data) [all of these are on the secondary resource part of the web site and on the
CLEAPSS Science Publications CD-ROM]. If none of these provide a hazard classification for a
chemical you wish to dispose, of contact CLEAPSS.
Any waste which is not hazardous can be disposed of in the normal refuse. This would include any low
hazard materials or hazardous materials at a sufficiently low concentration in a low hazard matrix (see
Hazcard W, code W8).
Effluent
Effluent is liquid that is poured down the foul water drain. However not all liquids and solutions can be
poured away, but as is so often the case, the distinction between permitted and not permitted is not
always clear.
List I. Those which cannot be poured down the drain include the following.
•
Mercury, cadmium and their compounds.
•
Organohalogen compounds, including tetrachloromethane, 1,1,1-trichloroethane and
trichloromethane.
•
Persistent mineral oils and hydrocarbons of petroleum origin.
•
Persistent synthetic substances, which may float, remain in suspension or sink and which may
interfere with any use of the waters.
•
Many insecticides and other pesticides.
List II. Some substances can be poured down the drain but the amount must be minimised. The list of
these substances is often referred to as the Grey List.
•
The following metalloids / metals and their compounds (see box for those marked “*”):
Antimony*
Arsenic
Barium
Beryllium*
Boron
Chromium*
Cobalt
Copper*
Lead*
Molybdenum
Nickel*
Selenium*
Silver*
Tellurium
Thallium
Tin
Titanium
Uranium
Vanadium*
Zinc*
Those marked * are often seen on lists of substances where the Trade Effluent Discharge Consent
permits no more than 10 mg / litre at the point at which it enters the public sewer.
© CLEAPSS 2010
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Even the most parsimonious secondary school is likely to discharge 14 litres of waste water per pupil
per school day (some, twice that amount). Thus every pupil in the school would be able to pour more
than 0.5 g copper sulfate down the drain every day and the school would still remain within the Trade
Effluent Discharge Consent Limits. CLEAPSS surveys suggest that the average secondary school uses
about 1821 g of copper sulfate per year. A 900-pupil secondary school could pour this amount down
the drain every day and still remain within the limits. Schools consume much smaller quantities of
almost everything else. So List II should not inhibit schools from disposing of the small amounts of
water-soluble chemicals that they use down the drain.
•
Biocides and their derivatives not appearing in List 1.
•
Substances that have a deleterious effect on the taste and/or smell of products for human
consumption derived from the aquatic environment and compounds liable to give rise to such
substances in water.
•
Toxic or persistent organic compounds of silicon and substances that may give rise to such
compounds in water, excluding those that are biologically harmless or are rapidly converted in
water to harmless substances.
•
Inorganic compounds of phosphorus and elemental phosphorus.
•
Non-persistent mineral oils and hydrocarbons of petroleum origin.
•
Cyanides, fluorides.
•
Certain substances which may have an adverse effect on the oxygen balance, particularly
ammonia and nitrites.
So, in general, chemicals that dissolve in water (W7 on Hazcards) can be disposed of down the drain
as effluent. Some, especially if present in larger quantities, will need neutralisation or other chemical
treatment (Wspec on Hazcards) to make them less hazardous. For acids and alkalis, aim at a pH of
between 5.5 and 9 which is achieved by adding sodium carbonate or ethanoic acid, as appropriate
(W4 and W5 on Hazcards). Some simply need dilution with large amounts of water. In such cases, it is
usually best to pour the contents of the buckets down a foul-water drain (ie, a toilet) and flush it away,
further diluting it.
Disposal into the atmosphere
Gases and vapours expelled from a ducted fume cupboard will go into the atmosphere. Certain
chemicals could be allowed to evaporate in a ducted fume cupboard or could be burnt on a small scale
(W6 on Hazcards)
The Montreal Protocol 1992 drastically reduced the production (and hence release) of ozone-depleting
chemicals. Substances such as tetrachloromethane and 1,1,1-trichloroethane can no longer be
purchased by schools. They must no longer be used for ‘diffusive purposes’. Note, however, that only
some chlorinated hydrocarbons are ozone-depleters, not all.