The University of Warwick
Physics Department
SAFE OPERATING PROCEDURE
FOR
THE USE OF HYDROFLUORIC ACID
AND
SOLUBLE FLUORIDES
Emergency number for internal phones: 22222
M. G. Dowsett
February 2013
1
The University of Warwick
Physics Department
SAFE OPERATING PROCEDURE FOR THE USE OF HYDROFLUORIC
ACID AND SOLUBLE FLUORIDES
1. Nomenclature
3
2. Introduction
3
3. Use of HF and soluble fluorides in the Physics Department
4
3.1 Approved users
4
3.2 The Operator – Observer (OO) Principle
4
4. Toxicity of HF and soluble fluorides
5
4.1 The effects
5
4.2 Routes into the body
6
5. First aid and subsequent steps
6
5.1 Introduction
6
5.2 The six steps in assisting a victim with fluoride exposure to the skin:
6
5.3 The four steps in assisting a victim of inhalation or ingestion
7
5.4 The four steps in assisting a victim with hydrofluoric acid splashed in their
eyes
7
5.5 A note on the use of calcium gluconate gel
8
6. Personal Protective Equipment (PPE)
8
6.1 Requirements
8
6.2 Dress code
9
6.3 Care and maintenance
9
6.4 Gloves
9
7. Working environment
10
7.1 The Chemicals
10
7.2 The Laboratory
10
7.3 The Work Station
11
7.4 Porterage
11
8. Materials for use with HF
12
9. Accidents and emergencies other than personal exposure
15
9.1 Power cuts
15
9.2 Spills inside the work station
15
9.3 Spills outside the workstation
15
10. Safe disposal
16
10.1 General procedure
16
10.2 Approved neutralizing agents, quantities and by-products
17
10.3 Neutralizing HF(aq)
17
10.4 Neutralizing sodium fluoride solution
19
10.5 Neutralizing other soluble fluorides and (hexa)fluorosilicic acid
20
11. Safe Working Regulations
21
References
22
Contact Sheet
23
2
The University of Warwick
Physics Department
SAFE OPERATING PROCEDURE FOR THE USE OF HYDROFLUORIC
ACID AND SOLUBLE FLUORIDES
Curiosity may have killed the cat, but curiosity about your work may save your life.
1. Nomenclature
DSO
Departmental Safety Officer
HF
Used here as a generic term for substances containing hydrogen
fluoride at any strength. The dangers of other soluble fluorides,
e.g. sodium fluoride, are similar, and this document applies to
all these, even where only HF is mentioned specifically. These
substances are extremely toxic because they are a source of
fluorine.
HF(aq.)
Used when referring specifically to the aqueous solution of HF
(hydrofluoric acid)
Hypocalcaemia
Lack of calcium in blood and body fluid – a principal cause of
death when fluorine gets into the body.
Hypomagnesaemia
Lack of magnesium in the blood and body fluids, also
extremely dangerous.
Spill kit
A proprietary kit to be kept by each workstation for use in the
event of a minor spill outside the workstation.
Work station
A fume cupboard, wet bench or other facility designated
specifically for the use of HF.
2. Introduction
HF is a virulent neurotoxin, a muscle inhibitor, and causes bone disintegration, all in
addition to its corrosive and tissue destroying effects as an acid. It is also hard for
emergency services to deal with because almost all the normal palliative actions
triggered by the word “acid” either have no useful effect, or make things worse. For
example, typical treatment for acid burns involves the use of a saline loaded dressing.
In the case of HF, this results in the local production of sodium fluoride which
exhibits exactly the same hazards as above with the addition of being mutagenic. HF
is readily absorbed through the skin, mucus membranes, and the lungs. HF(aq.) is an
effective source of HF gas, so the acquisition of lethal dose by inhalation is
straightforward. Untreated or incorrectly treated exposure to HF is usually fatal.
3
Rinsing an exposed area is inadequate on its own because the substance is so rapidly
absorbed that the internal consequences need to be dealt with at once. For example1,
in 1995 a laboratory technician in Perth (Australia) provided with totally inadequate
personal protection equipment (PPE) spilt about 100 ml of HF at an unknown
concentration down one leg. He immediately hosed the region off with water, called
the emergency services, and waited for them in a nearby swimming pool. He did not
apply any topical remedy (calcium gluconate gel was not available) and he did not
remove the affected clothing. Only 9.5% of his body area was exposed.
Nevertheless, although his leg was amputated and he received intensive treatment
designed to restore the calcium levels in his body, he died after 15 days from
hydrogen fluoride poisoning. It is suspected that a significant contribution to his
death was inhalation of HF gas from the spill in the first few seconds of the accident.
These rules are intended to ensure that nothing remotely like this ever happens here.
3. Use of HF and soluble fluorides in the Physics Department
3.1 Approved users
The use of HF is governed by the local rules contained in this document. HF and
related substances may only be handled in a work station or fume cupboard
designated specifically for the purpose. Only individuals on the list of Approved
Users may work with these materials. To become an Approved User it is necessary
to take the Department’s HF safety course and pass the associated tests. A detailed
knowledge of this document will be expected.

Under no circumstances will undergraduates be allowed to work with HF or
soluble fluorides.

The devolution of responsibility for working with HF to an untrained person is
a disciplinary offence.

Approved Users do NOT have a mandate to give training.
3.2 The Operator – Observer (OO) Principle
The Department’s safety procedure is based on the operator-observer (OO)
principle. An individual working with HF (the operator) will be accompanied at all
times by an observer.

The operator’s role is to run the necessary process in accordance with the rules
herein.

The observer’s role is to render immediate assistance in the event of an
accident where this is consistent with their own personal safety, to summon
more general first aid, to ensure that the emergency services are called, to
make sure that any other necessary action is taken (this may include
evacuation of the laboratory or the building) and, if necessary, to act as a
source of information on HF to ensure that any medical or hospital treatment
is relevant to the problem. To ease the latter role, a contact sheet is provided
4
at the end of this document and should be presented to medical, paramedical
or casualty staff.

The OO principle applies equally to work in the laboratory and to carriage of
materials between approved stores and the laboratory. i.e. ONLY approved
users may carry containers of HF around the building and they must be
accompanied by an observer.
4. Toxicity of HF and soluble fluorides
4.1 The effects
The reaction between calcium and fluorine ions in solution goes like this:
Ca++ + 2F-  CaF2
The calcium is precipitated as insoluble calcium fluoride. This is both the key to
making the substance safe, and to its deadly action on the humans and animal life
generally. The viability of the human body depends on calcium ions in solution in
body fluids. Calcium ion exchange plays a key role in both neurotransmission and
muscle action. The action of any fluorine ions entering the body is to precipitate the
calcium causing severe hypocalcaemia. (HF also gives rise to a similar effect on
magnesium causing hypomagnesaemia.) Fluorine ion absorption inhibits vital
processes first locally, and very soon afterwards (as little as 15 s for a severe
exposure) systemically. Localized exposure may go unnoticed because the sharp
pain which would be felt with another acid is dulled by the killing of the pain
receptors, and their links to the brain.
The effects of exposure are highly variable and may not result in obvious symptoms
until hours or even days afterwards.
Depending on the level of exposure they include








severe tissue damage resulting in mortification of bones, muscles, skin, etc.
extreme pain, a dull ache, lack of sensation
paralysis
shock
confusion
massive organ failure
unconsciousness
death
Absorption of fluorine ions can cause long term damage. The bones are attacked and
their microscopic cross-linked structure is destroyed. The resulting material has no
mechanical strength and collapses leaving the tissue unsupported. For example,
during World War II a female technician working with hydrofluoric acid in the early
days of uranium separation was exposed repeatedly through an unnoticed pin hole in a
glove. The technician survived, but lost her hand because of the severe bone and
tissue damage. Some version of this accident has occurred repeatedly since then2,3,
5
and even where the victim survives, recovery is painful and can take months or even
years3.
4.2 Routes into the body




ingestion –
the substance is swallowed
inhalation – the vapour is breathed
instillation – the substance is absorbed via the eyes or the nose following
exposure to droplets
absorption – entry is through the skin
5. First aid and subsequent steps
5.1 Introduction
Past fatalities have occurred for two reasons only.
(i) Massive untreatable exposure.
(ii) Treatment failure following exposure (delayed, incorrect or none).
Individuals have been killed by exposures of 2.5% of body area or less to
concentrated HF(aq) because of poor post exposure treatment.
Conversely,
exposures as high as 22% have been survived where the correct measures were taken
immediately.
IN ALL CASES, SUSPECTED EXPOSURE SHALL BE TREATED AS
EXPOSURE.
The Observer is responsible for the giving of immediate HF specific first aid.
At the earliest opportunity phone 22222 (or get someone else to do this) and arrange
for an ambulance. You may also summon help from Departmental First Aiders.
5.2 The six steps in assisting a victim with fluoride exposure to the skin:

Make the area safe and take precautions to make sure that neither you, nor
anyone working nearby, is jeopardized. This may entail other personnel
leaving the laboratory. Don the appropriate protective equipment (see §6,
Personal Protective Equipment).

Remove all affected clothing as rapidly as possible, but with as little further
contact to the affected individual as possible. Lay this aside safely (e.g. in a
bucket of water in the work station for later safe disposal or double bagged in
polyethylene bags). DO NOT RINSE THROUGH CLOTHING – this will
spread the problem around.

Rinse/sluice off the affected area for 3-5 minutes with copious quantities of
fresh water in a jet or from a soft dispersal nozzle.
6

Immediately apply liberal quantities of calcium gluconate gel to the affected
region. Keep on rubbing this in both locally and around the affected area.

The victim MUST be removed to hospital, and calcium gluconate treatment
MUST be continued in the ambulance (see Contact Sheet).

Medical and paramedical staff must be made aware that the patient has been
exposed to hydrogen fluoride (see Contact Sheet) and that the remedial
treatment differs from that for other acids.
5.3 The four steps in assisting a victim of inhalation or ingestion
(May be required additionally to 5.2)

Make the area safe and take precautions to make sure that neither you, nor
anyone working nearby, is jeopardized (see §6, Personal Protective
Equipment).

If the victim has HF splashed in the nose, apply calcium gluconate gel directly
to the inside of the nostrils, do not attempt irrigation.
OR
If the victim has swallowed HF wash the mouth out with a cup of water. Do
not give large quantities to drink. Do not induce vomiting. It may be useful to
give about half a cup full of water, milk, or anti-acid (e.g. Milk of Magnesia in
water). If the victim vomits spontaneously, assist them with physical support.
The vomit should be treated as an HF hazard.

The victim must be removed to hospital as soon as possible, even if there are
no visible signs of exposure.

Medical and paramedical staff must be made aware that the patient has been
exposed to hydrogen fluoride vapour by inhalation or has ingested the liquid
(see Contact Sheet) and that specialized poisons treatment is urgently required.
5.4 The four steps in assisting a victim with hydrofluoric acid splashed in their
eyes

Make the area safe and take precautions to make sure that neither you, nor
anyone working nearby, are jeopardized (see §6, Personal Protective
Equipment).

If available, immediately treat with Hexafluorine eyewash according to the
instructions. OR Rinse the affected area with copious quantities of fresh water
from a soft dispersal nozzle, or using a non-saline eye wash.
7

The victim must be removed to hospital as soon as possible, even if there are
no visible signs of exposure.

Medical and paramedical staff must be made aware that the patient has been
exposed to hydrogen fluoride by instillation (see Contact Sheet) and that
specialized poisons treatment is urgently required.
An accident where an individual has the liquid spilt on their skin may also involve
spillage of hydrofluoric acid on the floor or exterior bench work. This must be made
safe where possible and the affected laboratory must be evacuated by non-essential
personnel. In the case of a larger scale spill (> 500 mL at > 30% w/w) it will be
necessary to evacuate the building and call the Fire Brigade.
5.5 A note on the use of calcium gluconate gel
Calcium gluconate gel feels cold and sticky and dries on the skin to form a white
peeling crust. Moreover, the underlying skin will appear to be red and inflamed, even
if there has been no exposure to HF. The white peeling surface and the red skin
below looks superficially like severe skin damage and may prompt medical staff to
react in the wrong way. See the Contact Sheet at the end of this document.
6. Personal Protective Equipment (PPE)
6.1 Requirements
Adequate PPE can reduce a potentially lethal event to a minor inconvenience.
For hydrofluoric acid, the Department works on the basis of informed personal
responsibility for PPE.
i.e. Each individual authorized to work with HF will be supplied with and maintain
their own PPE (with the exception of disposable gloves which will be available at the
work stations). PPE will not be shared between individuals. Suspect PPE will be
immediately destroyed and replaced. The responsibility for checking the integrity of
PPE rests with the individual using it.
The minimum PPE for working with hydrofluoric acid or soluble fluorides inside an
approved workstation is:





Full face splash proof visor to EN166 1 B 3 or better
Hydrofluoric acid resistant full length, long sleeved smock
Hydrofluoric acid resistant boots
Disposable hydrofluoric acid resistant gloves (two pairs, both to be worn) or
long HF resistant gloves (elbow or shoulder length) with a pair of disposable
gloves worn inside
Disposable HF nuisance mask e.g. 3M 9906 (for spills and porterage)
An individual giving first aid will need at least:
8


Disposable hydrofluoric acid resistant gloves (two pairs, both to be worn)
Disposable HF nuisance mask.
Some or all of the following may also be necessary depending on the level and
concentration of the exposure



Full face splash proof visor to EN 166 1 B 3 or better
Hydrofluoric acid resistant full length, long sleeved smock
Hydrofluoric acid resistant boots.
6.2 Dress code
1. The sleeves of the smock must be outside the gloves and not tucked into them,
unless the gloves are elbow length or more.
2. The bottom of the smock must have an overlap of at least 150 mm with the tops of
the boots, and must be worn outside them. i.e. it must not be possible for liquid
splashed on the smock to flow into the boots or gloves.
6.3 Care and maintenance
The storage and care of an individual’s PPE is their own responsibility. If HF is spilt
on the PPE, the affected item must immediately be carefully rinsed or sluiced off, in
the workstation or the emergency shower nearby. It may well be best to do this
without removing the item. This counts as a procedure involving HF and is subject to
all the rules herein. In particular, the process must not create an additional hazard for
the PPE owner or others in the vicinity.
Items must be thoroughly clean and dry prior to storage.
The user must be assured of the integrity of the clothing, and any doubtful items must
be replaced.
6.4 Gloves
GLOVES DO NOT MAKE YOU SAFE!
The most common cause of HF exposure is a pinhole in a glove, so pay special
attention to these.
There appears to be no rigorous scientific basis for the recommendation of any
common glove material over any other. Company representatives simply do not have
the specialized knowledge to help with a recommendation and merely repeat what it
says in their catalogue. None out of natural rubber, Nitrile, Polychloroprene, Vinyl,
Neoprene or the rest forms anything more than a short term barrier and the author is
not aware of reliable tests of any of these materials above HF strengths of 48%
anyway. Worse still, different sources (even from the same supplier) conflict about
their relative effectiveness, some rating natural rubber as the best, some extolling
Nitrile, and some claiming neither can be used.
9
What is true is:







Gloves of whatever type must be seamless
Gloves only ever offer splash protection.
You must NEVER immerse gloved fingers in HF
ANY glove splashed with HF should be rinsed, removed and discarded (in that
order).
All gloves are permeable to HF except (possibly) as noted below.
If you use outer gloves which are “non-disposable” they must be replaced as
above if splashed, and in any case every six months.
A typical suppliers disclaimer is that a purchaser is responsible for testing
gloves themselves.
Gloves should be worn like this:





Wear your gloves for 30 minutes at most.
Rinse the outer pair and discard if they are disposable.
Rinse the inner pair and discard.
Wash your hands.
Don new gloves.
Linear low density polyethylene (LLDPE) gloves provide the most resistance in any
published test and this is consistent with the material properties as listed in reference
4. They are hard to source.
7. Working environment
7.1 The Chemicals
Open HF containing vessels must not be taken outside a workstation. Open HF
containing vessels must never be left unattended except in an emergency. All
chemicals which are left unattended, or which are to be transported, must be in closed
containers made from suitably resistant materials and have secure lids. Such
containers must be clearly and indelibly labelled with the name of the chemical they
contain and its strength. Chemicals in sealed containers must be returned to an
appropriate store and not left in the work station.
7.2 The Laboratory
The laboratory environment must be clear and uncluttered with free access to the
emergency shower and sinks. There will be no loose items on the floor. Work
benches will contain the minimum amount of equipment and containers required for
the processes under way. Unused materials and equipment will be put away
immediately. Sinks and drainers will not be left covered in chemical ware requiring
cleaning.
10
7.3 The Work Station
The working surfaces in the work station will be kept clear and uncluttered using the
minimum amount of space for chemical containers and equipment. The work station
will not be used to store chemicals. HF resistant materials (see §8) will be used for
vessels and equipment in the workstation. The safety equipment listed in Table 1 will
be available immediately adjacent to any workstation using HF or soluble fluorides in
the Physics Department. The operator and observer should ensure that this is the case
before commencing work.
What
Minimum quantity
Comment
Small tubes are not acceptable.
Calcium gluconate gel
2 x 500 g tubs
Topical application to exposed skin.
Wall mounted grab
Effective chelation and barrier for HF
Hexafluorine eye wash
pack
in eyes or on face
Essential chaser if HF swallowed
Milk of magnesia
1 x 200 mL bottle
(MgO chelates fluorine ions)
Natural rubber, nitrile or neoprene.
MUST BE SEAMLESS.
Gloved hands must NOT be immersed
in HF.
No gloves exist which form a
permanent
impermeable barrier to HF.
If gloves are splashed, rinse
S, M, L, and XL
remove, discard immediately.
to be supplied
Wear two pairs, or one pair inside
Snug fit disposable gloves 1 pk 100 in use,
"non disposable" gloves.
(surgical glove style)
1 pk 100 full
Do not wear for more than 30 min.
High proportion of MgO,
suitable for spills outside work
Spill-X-A powder
1 x 22.7 kg plastic pail stations
Spill-X-A powder
1 x 1.1 kg container For small spills
Table 1: Minimum level of safety equipment to be provided adjacent to a work
station.
Work with the sash in the lowest practical position, and never raise the sash above the
maximum level marked when the work station contains any HF. Never put your head
inside the workstation when attempting to clean up spills.
7.4 Porterage
From time to time it will be necessary to carry HF or a related substance through the
building to the laboratory where it is to be used. The following procedure will be
adopted.
11





Porterage must be planned in advance and carried out when the levels of
traffic on stairwells and in corridors is low (e.g. avoid the period between fiveto and five-past the hour during term time).
Lifts must not be used.
The OO pair will carry HF resistant disposable gloves and HF nuisance masks
to be worn in the event of an emergency.
The operator will carry the material in an approved container which must be
sealed and in a bottle carrier or crate.
The observer will accompany them (walking in front) to assist with
appropriate action in the event of a spill. (See §9)
8. Materials for use with HF
HF dissolves silica and silica related materials such as glass, so these materials must
not be used with HF at any strength. The substance also causes stress cracking in
polymer and resin based materials such as polypropylene and acrylic (e.g. Perspex®)
so these materials can become defective and must not be used. (An exception to this
is the use of polypropylene containers made from sheet welded at the edges. These
containers must be limited to a maximum of 40% w/w HF(aq), and users are advised
to inspect them regularly for evidence of failure.) Many other polymers are suitable
for the containment of HF, especially fluoropolymers (with the exception of
fluorinated polyethylene (FPE)). Polyethylene itself is also suitable up to quite high
concentrations. Suitable fittings and pipework are commercially available in PVDF,
ETFE and PTFE, and polyethylene, PTFE, PVDF, PCTFE, are suitable materials for
vessel fabrication or purchased chemical ware. They are available as rod or sheet, and
may be welded by a specialized fabricator. Polyethylene is difficult to machine
successfully, but is excellent in cast and injection moulded items. PTFE and PCTFE
can be machined readily to a good surface finish and tolerances significantly smaller
than 0.1 mm. PCTFE is harder and more dimensionally stable and is more suitable
for threading and intricate detail, but it is much more expensive. All polymers have
high expansion coefficients in comparison to metals (>120 ppm / °C compared to 720 ppm / °C). For sealing materials (e.g. gaskets and O rings) you should seek
specific information according to the application.
Note that all fluoropolymers decompose to emit or become coated with HF if heated
excessively. (Typically excessive heating means over 300 °C or burning.) They
therefore become hazardous in their own right and are regularly the cause of
accidents.
Table 2 gives more information on limitations and range of use of common
engineering polymers and speciality fluoropolymers.
NEVER USE POLYMERS CONTAINING FILLER SUCH AS FLUROSINT.
POLYMERS SHOULD BE “NATURAL” OR SIMPLY PURE.
Fluoropolymers may not be cast or welded in the Physics Department as this requires
specialized facilities.
Caution must be exercised when machining fluoropolymers. Sharp tooling is
required, and the work must not overheat.
Never smoke whilst handling
12
fluoropolymers or fluorpolymer waste – the dust is converted to HF when it is drawn
into a cigarette.
13
Acronym/
Trade
Max % at
name
20 °C

®
Delrin

Max % at
30 °C


Perspex®
<20%
ETFE
FPE

100 % (anhydrous)
at 23 °C
Comments


Limited use for <1 day, not
recommended

4
70 ✓

70 ✓

Not listed

5
4
High density polyethylene HDPE
Low density polyethylene LDPE
Medium density
polyethylene
MDPE
60 ✓
40 ✓
60 ✓
40 ✓


60 ✓
60 ✓

Polychlorotrifluoroethylene PCTFE
Polyetheretherkeytone
PEEK
60 (23°C) ✓

Not listed

✓(7 Days)

Common Name
Acetal Copolymer
Acetal Homopolymer
Acrylic
Ethylene
Tetrafluoroethylene
Fluorinated polyethylene
Polyethylene cross linked
Polyimide
XPE
Kapton®

40 ✓

40 ✓
Not listed
Not listed
Polypropylene
PP
40 ✓ Not
injection
moulded
40✓ Not injection
moulded

Polytetrafluoroethylene
Polyvinylidene fluoride
PTFE
PVDF
60✓
70✓
60✓
70✓
✓(Time not listed)
✓(7 Days)
Slight permeability above 60%.
Resistance varies with form.
Sources
4
4
4
4,6
4
Longer exposures at 100%
result in discoloration
Not suitable - may stress crack
at any concentration
Test duration 4 days
Stress cracking observed at higher
concentration. Do not use injection
moulded products (e.g. Azlon®
beakers)
Never use filled or sintered PTFE
(e.g. Fluorosint)
Exposure at ≤ 70% is >30 days
5
5
5
5
4,6
5
5
Table 2: Suitability of various polymers for use with HF(Aq) and NaF (aq).  Not suitable.  Suitable (with limitations).
14
9. Accidents and Emergencies other than personal exposure
9.1 Power cuts
Power cuts are not uncommon. All laboratories approved for HF use must have
emergency lighting. In the event of a power cut the extraction on the workstation or
fume cupboard with stop.
You must cover any open sources of HF if it is safe and practical to do so.
All personnel must leave the laboratory and the doors must be shut.
The laboratory must not be re-entered until one hour after the extraction has restarted.
(Or until tests with an HF detector show that it is safe.)
9.2 Spills inside the work station
If it is safe and practical to do so, neutralize the HF in situ (see §10, Safe Disposal).
In any case flush the HF away with a large quantity of water (large means at least 100
times the volume of split material) taking care that there is no splash back out of the
workstation onto yourself. Ensure that no HF remains on any surfaces or in the sump
underneath the workstation. If necessary, after rinsing off the perforated bench work,
lift this up carefully and clean the under side, and the sump.
9.3 Spills outside the workstation
All unprotected personnel must leave the laboratory or the area at once.
In the event of a catastrophic spill in the laboratory (for example the disruption of a
full container of concentrated acid):



Deal appropriately with personal exposure, summoning help to deal with other
matters.
Evacuate the laboratory, sound the fire alarm and leave the building.
Continue the treatment of an exposed person using copious amounts of
calcium gluconate gel to neutralize unrinsed acid.
You must contact a fire marshal (wearing a yellow day glow tabard), the DSO,
the Departmental Administrator, The Head of Department or any other senior
member of staff at the first opportunity after leaving the building and explain
the circumstances. DO NOT ATTEMPT TO DEAL WITH THE SPILL.
In the event of a catastrophic spill on a stairwell:


Personal injury (e.g. exposure) to the operator must be dealt with first. In
such an event, the observer must immediately summon help so that the rest of
the procedure can be carried out whilst first aid treatment is given.
Provided they are uninjured, the operator will don an HF nuisance mask and
remain in the vicinity to prevent others from going near the spill until 1 minute
after the fire alarm has sounded.
15


The observer will contact the DSO, the Departmental Administrator or the
Head of Department who will take whatever measures are needed to ensure
that the stairwell remains unused (e.g. deputation of Fire Marshals and the
observer).
Only when this has been done, sound the fire alarm and evacuate the building.
In the event of a non-catastrophic spill:



The operator and observer will don HF nuisance masks, gloves and face
shields.
Other personnel will evacuate from the laboratory, or be warned away from
the site.
The operator will then contain and neutralize the spill using the dry material
from a Spill-X® tub as follows:
1.
2.
3.
4.
Do not lean over the spill
Using the Spill-X-A powder to make a dam around the spill
Gently apply a large quantity of Spill-X-A onto the spill
After 10 minutes collect and store the solid product for waste disposal.
10. Safe disposal
10.1 General procedure
Bear in mind that HF(aq) above 50% reacts violently and exothermally with water,
and violently with glass and other silicon containing materials such as concrete. This
will result in the emission of extremely toxic fumes of HF or SiF4 (silicon
tetrafluoride).




Dilution, if required, should be gradual. Concentrated acid should be added to
water.
Glass or silica containers must be avoided at all stages.
Except in the event of a spill, the procedure will take place inside a work
station
In the event of a small spill outside a work station, a breathing mask will be
required (see §6).
Calcium and magnesium fluorides have very low solubilities in water and solutions of
these do not represent a significant hazard. The safe disposal of HF or soluble
fluorides involves




Do not add water to concentrated acid (>20%).
Slowly add a precipitating agent to the correct amount (note for large
quantities of high strength solution this may take several hours or even days).
Check that the reaction is complete (except where calcium chloride has been
used, the solution should be pH neutral or slightly alkaline).
For neutralization of solutions containing less than 10 g of anhydrous HF at
any strength the residues may be flushed down the drain at a dilution with
water of at least 100:1
16

Larger quantities must be placed in an authorized container, clearly labelled,
and sent for chemical waste disposal.
10.2 Approved neutralizing agents, quantities and by-products
The Department approves the compounds in Table 3 as neutralizing agents:
Compound
Calcium
carbonate
Calcium
hydroxide
Formula* Comment
Evolves
CaCO3
CO2
CaCl2
Magnesium
oxide
MgO
CaCO3 + 2HF  CaF2+ CO2 + H2O
Ca(OH)2 + 2HF  CaF2 + 2H2O
Ca(OH)2
Calcium
chloride
Reaction
Small
amounts of
HF only.
Use for NaF
CaCl2 + 2HF  CaF2 + 2HCl
CaCl2 + 2NaF  CaF2 + 2NaCl
MgO + 2HF  MgF2 + H2O
Table 3: Approved neutralizing agents and their reactions. *Note: Formulae do not
include water of crystallization and so are not necessarily indicative of molar mass.
Sodium compounds and other compounds where the reaction produces a soluble
fluoride are not permitted for neutralization of HF (even though you will find them
recommended elsewhere). Calcium chloride may only be used for the neutralization
of solutions containing up to 10 g of anhydrous HF (or 25 g of NaF) whatever their
strength, as CaF2 is slightly soluble in hydrochloric acid. This must be flushed to
waste with water at a ratio of 100:1. Neutralization of the HCl with alkali is
undesirable because the CaF2 is also soluble in alkaline solutions.
10.3 Neutralizing HF(aq)
The strength of HF is normally quoted as a percentage. This is percentage by mass
and is given by P where:
P
Weight of HF
 100
Weight of solution
.
1
So, for example, if I have 100 g of 40% HF(aq) it contains 40 g of hydrogen fluoride.
One mole of a substance contains Avogadro’s number (6.022  1022) of molecules of
that substance. The mass of one mole in grams (the molar mass) is obtained by
adding up the atomic masses of its constituent atoms in Daltons, including any water
of crystallization. The molar mass of HF is therefore 20 g, so the 40 g of HF above is
2 mol. of the substance. At 20 C, the specific gravity of 40% HF is 1.13, so 1 L of
solution weighs 1.13 kg and will contain 452 g or 22.6 mol of HF.
A 40% solution therefore has a molarity of 22.6 (i.e. there are 22.6 mol. HF per litre
of solution -which is extremely high).
17
The room temperature (20 C) molarity, MHF, can be calculated from the weight
percentage P of the HF from
M HF  0.565P .
2
Because one atom of calcium and magnesium each lock away two atoms of fluorine,
it takes 0.5 mol of one of the calcium or magnesium salts listed in Table 3 to
neutralize 1 mol of HF.
When calculating the weight of neutralizing agent required it is essential to know
whether it is anhydrous or not, and take account of any water of crystallization in the
formula. Molar masses for common forms of the approved agents are given in
Table 4. The molecular weight can normally be found on the manufacturer’s
packaging.
Compound
Anhydrous calcium
chloride
Calcium chloride
dihydrate
Calcium carbonate
Calcium hydroxide
Magnesium oxide
Hydrogen fluoride
Sodium Fluoride
Magnesium fluoride
Calcium Fluoride
Formula
CaCl2
Molar mass Wm / g
110.98
Solubility
74.5
CaCl2 2H2O
147.01
74.5
CaCO3
Ca(OH)2
MgO
HF
100.09
74.09
40.30
20
NaF
MgF2
CaF2
42
62.30
78.07
0.00153
0.12
0.0006
Miscible in any
proportion
4.06
0.013
0.0016
Table 4: Molar masses of the common forms of the approved neutralizing agents, and
fluorine containing substances together with their solubilities in grams per
100 g of water7.
As a rule, the operator will know the volume of HF(aq) they are using V in mL (rather
than the mass), and its percentage strength P. In order to determine the number of
moles of HF in the solution, the density  is required (g cm-3 in Equation 3, below).
This is given in Figure 1 as a function of P with temperature as a parameter. Then the
number of moles of HF in the solution is given by
M HF 
P V
.
100 20
3
The minimum weight in grams wmin of neutralizing agent for this number of moles
will be
wmin  0.5M HFWm 
P VWm
,
4000
4
18
where Wm is obtained from Table 4. In practice, 10% extra of neutralizer should be
added to a level wsafe, so, finally, in grams:
For HF
wsafe  2.75  10 4 P VWm .
5
Figure 1: Density of HF(aq) as a function of percentage concentration9,10.
Temperature is a parameter.
10.4 Neutralizing sodium fluoride solution
Saturated solutions must first be diluted with water until there is no solid residue.
The maximum amount of NaF in aqueous solution at room temperature will be in the
range 4.0-4.2 g per 100 ml of water7. This is sufficient to kill. In acidic or other
solutions the concentration may be higher. Normally, sodium fluoride solution will
have been made up by the operator to a known percentage or molarity, or will be
present in a proprietary etch at a known concentration.
19
Calcium chloride solution is convenient for the neutralization of sodium fluoride
solution, precipitating out the fluorine ions as CaF2 (see Table 3). The result is a
white, gelatinous precipitate of calcium fluoride8.
The molar mass of NaF is 42 g so, by analogy with Equation 3, the number of moles
of NaF in a solution percentage P, volume V, solution density NaF will be:
M NaF 
P  NaFV
.
100 42
6
Then the safe weight of neutralizer (in grams) is given by:
For NaF
wsafe  1.31  10 4 P  NaFVWm .
7
Wm must be selected for the appropriate form of calcium chloride (see e.g. Table 4).
However, it is unlikely that NaF will be known in practice, so it is simpler to proceed
from the molarity of the solution, MNaF, if known, or from the weight of NaF in
grams, wNaF actually used. In the former case, for a volume of solution V in mL, the
safe weight of neutralizer in grams will be,
For NaF
wsafe  5.5  10 4 VM NaFWm ,
8
wsafe  1.31  10 2 wNaFWm .
9
and in the latter,
For NaF
10.5 Neutralizing other soluble fluorides and (hexa)fluorosilicic acid
Fluorosilicic acid is formed in a mixture with hydrofluoric acid when siliceous
material has been dissolved. It evolves two highly toxic gases, silicon tetrafluoride,
SiF4 and HF. Neutralization should proceed in a similar way to that for HF, but
specific reactions with the neutralizing agents should be checked.
Other soluble fluorides should be neutralized according to the general principles in
§10, modifying the amounts of neutralizing agent according to the molar weight of the
substance. Care should be taken that reaction routes do indeed result in the
precipitation of calcium or magnesium fluoride, and where doubt exists, a small
quantity should be tested prior to any large scale experimentation.
20
11. Safe Working Regulations
1. Only Approved Users authorized by the Departmental Safety Officer (DSO)
may work with HF or soluble fluorides.
2. The operator must have completed the COSHH Hazard Assessment Procedure
prior to commencing the process. In the case of PhD students there must be
documentary evidence that the supervisor has seen the relevant content of the
student’s laboratory notebook and any supplementary notes made during the
procedure.
3. Lone working is absolutely forbidden. An operator must have an observer
within eyeshot. The observer must also be an approved user.
4. Procedures (other than those requiring no intervention) involving HF or
soluble fluorides must only be carried out between 08:00 and 18:00.
5. An HF designated workstation must be used.
6. HF resistant materials must be used for all containers, stirrer flees, tweezers
etc.
THE USE OF GLASS, FUSED SILICA (QUARTZ), AND INJECTION
MOULDED POLYPROPYLENE EQUIPMENT IS PROHIBITED.
7. Only a single operator may run a process in a workstation at any one time.
8. An operator must wear the specified PPE.
9. Operator and observer MUST assure themselves that in-date HF gluconate gel,
disposable HF resistant gloves, Hexafluorine eyewash, HF nuisance masks,
and an HF spill kit are available adjacent to the workstation before
commencing work.
10. The observer must have their PPE to hand in case of need.
11. Processes above room temperature are not permitted under these rules and will
require special safety approval.
12. HF may not be taken outside a workstation or transported through the
Department in any quantity at any strength except in a sealed high density
polyethylene container. (Other materials may be suitable, see Table 2.) The
container must be carried in a bottle carrier or a custom designed carrier
approved by the DSO. Porterage between the chemical store and the point of
application is allowed. Porterage between different laboratories is prohibited
(e.g. you may not mix an etch in one place and use it elsewhere).
13. HF may only be stored in an extracted cupboard or ventilated area approved
for the purpose by the DSO.
14. Spillages outside the workstation MUST be reported to the DSO
15. Individuals exposed to HF, HF(aq) or soluble fluorides must be given
immediate first aid and the emergency services must be called.
16. Ignoring these rules, encouraging others to ignore them, and devolving any
responsibility for working with HF to personnel who are not Approved Users,
are all disciplinary offences.
21
References
1. L. Muriale, E. Lee, J. Genovese and S. Trend, Ann. occup. Hyg. 40 (1996) 705-710
2. L. R. Goldfrank, The Journal of Emergency Medicine 17 (1999) 1055-1064
3. http://cint.lanl.gov/source/orgs/mpa/cint/integration_lab/docs/MED105HF.pdf
accessed February 2013.
4. W. A. Woishnis and S. Ebnesajjad (Eds.), Chemical Resistance of Thermoplastics,
Elsevier Inc. 2012.
5. W. A. Woishnis and S. Ebnesajjad (Eds.), Chemical Resistance of Speciality
Thermoplastics, Elsevier Inc. 2012.
6. ISO/TR 10358:1993 Plastics pipes and fittings; combined chemical-resistance
classification table, International Standards Organization 1993
7. Kaye and Laby, Tables of Physical and Chemical Constants,
http://www.kayelaby.npl.co.uk
8. R. C. Saunders (Ed.), Fenton’s Notes on Qualitative Analysis, Cambridge University
Press (1951), p28.
9. Kirk-Othmer Encyclopedia of Chemical Technology, 2nd Edition, Volume 9 (1996)
610-625
10. Anhydrous hydrogen Fluoride and Hydrofluoric Acid Physical Properties, Solvay
Special Chemicals,
http://www.solvaychemicals.com/Chemicals%20Literature%20Documents/Fluor/HF_
Inorg_Fluoride/HF_Physical_Properties.pdf
22
The University of Warwick
Department of Physics
HAZARD CONTACT SHEET
Aqueous solution of hydrogen fluoride (hydrofluoric acid)
Hydrogen fluoride gas
Other soluble fluorides in solution or solid form
The casualty has been in contact with one of the above substances and
may be suffering from acute poisoning due to absorption, ingestion,
inhalation or instillation.
Please seek immediate advice from a toxicologist.
Appropriate first aid treatment using calcium gluconate gel. (skin exposure),
Hexafluorine (eyes), Milk of Magnesia, or similar (ingestion) may already have been
given. The casualty may already have been externally decontaminated. The
accompanying person can give more information.

Medical staff should take precautions to minimize risk to themselves
should the casualty still be externally contaminated. This may include
an HF nuisance mask. Two pairs of surgical gloves and eye protection
should be worn when initially handing the patient. Gloves should be
rinsed prior to removal to prevent inadvertent contact with the
substance.

Vomit should be treated as chemically hazardous as it may be
contaminated with HF.

The casualty may
hypomagnesaemic.

Symptoms such as paralysis, loss of sensation, shock, severe burning,
confusion, unconsciousness may be apparent immediately, or may
develop over several days, depending in the level of exposure.
be,
or
become,
hypocalcaemic
and
Professor Mark Dowsett
Department of Physics
The University of Warwick
Coventry, CV4 7AL
Phone: 02476 523900
Emergency only: 07855 269693
23