HT6
FREE AND FORCED CONVECTION
HEAT TRANSFER
HT6
ISSUE 11
MARCH 1998
ARMFIELD LIMITED
OPERATING INSTRUCTIONS AND EXPERIMENTS
HT6
PAGE NO.
SAI-ETY
1
INT'RODUCTION
5
REC'EIPT OF EQUIPMENT
6
DEE,CRIPTION
8
INSTALLATION REQUIREMENTS
10
COI@NECTION TO SERVICES
11
C014MISSIONING
12
ROIJTINE MAINTENANCE
15
IND,EX TO EXPERIMENTS
16
GE@@RAL SAFETY RULES
a
SAFETY IN THE USE OF EQUIPMENT SUPPLIED BY ARMFIELD
Befiz)re proceeding to install, commission or operate the equipment described in this
instruction manual we wish to alert you to potential hazards so that they may be
avoided.
Alt]4ough designed for safe operation, any laboratory equipment may inv@Dlve
processes or procedures which are potentially hazardous. The major potential
hazards associated with this particular equipment are listed below.
~
INJURY THROUGH MISUSE
0
INJURY FROM ELECTRIC SHOCK
0
INJURY FROM ROTATTNG COMPONENTS
0
BURNS FROM COMPONENTS AT HIGH TEMPERATURES
Accidents can be avoided provided that equipment -@s regularly maintained and
staff and students are made aware of potential hazards. A list of general safety rules
is included in this manual, to assist staff and students in this regard. The list is not
intended to be fully comprehensive but for guidance only.
Pleikse refer to the notes overleaf regarding the Control of Substances Hai,,ardous to
Health Regulations.
I
The COSHII Regulations
The Control
(1988)
of Substances
Hazardous
to Health
Regulations
The COSHH regulations impose a duty on employers to protect employees and
others from substances used at work which may be hazardous to health. The
regulations require you to make an assessment of all operations which are liable to
expose any person to hazardous solids, liquids, dusts, vapours, gases or microorganisms. You are also required to introduce suitable procedures for handling these
substances and keep appropriate records.
Since the equipment supplied by Armfield Limited may involve the use of
substances which can be hazardous (for example, cleaning fluids used for
maintenance or chemicals used for particular demonstrations) it is essential that the
laboratory supervisor or some other person in authority is responsible for
implementing the COSHH regulations.
Part of the above regulations are to ensure that the relevant Health and Safety Data
Sheets are available for all hazardous substances used in the laboratory. Any person
using a hazardous substance must be informed of the following:
Physical data about the substance
Any hazard from fire or explosion
Any hazard to health
Appropriate First Aid treatment
Any hazard from reaction with other substances How
to clean/dispose of spillage
Appropriate protective measures
Appropriate storage and handling
Although these regulations may not be applicable in your country, it is strongly
recommended that a similar approach is adopted for the protection of the students
operating the equipment. Local regulations must also be considered.
USE OF RESIDUAL
SAFETY DEVICE
CURRENT
DEVICE
AS AN ELECTRICAL
The equipment described in this Instruction Manual operates from a mains
voltage electrical supply. The equipment is designed and manufactured in
accordance with appropriate regulations relating to the use of electricity.
Similarly, it is assumed that regulations applying to the operation of electrical
equipment are observed by the end user.
However, it is recommended that the Residual Current Device (RCD) supplied
alternatively called an Earth Leakage Circuit Breaker - ELCB) be fitted to this
equipment. If through misuse or accident the equipment becomes E!Iectrically
dangerous, an RCD will switch off the electrical supply and redu(,e the severity of
any electric shock received by an operator to a level which, under normal
circumstances, will not cause injury to that person.
If the electrical supply to the laboratory already incorporates an RCD, then the device
supplied with the equipment need no@-be used. If the electrical supply does not
incorporate such protection then the loose RCD supplied by ArmfiE!ld Ltd should
be fitted by a competent electrician either in the supply tc, the laboratory or in the
supply to the individual item of equipment. Drawing Number BM20491 gives full
installation instructions.
Note: If any doubt exists whether the electrical supply incorporates a deirice then the
RCD supplied should be fitted.
At least once each month, check that the RCD is operating correctly by pressing the
TEST button. The circuit breaker MUST trip when the button is pressed. Failure to
trip means that the operator is not protected and the equipment must be checked and
repaired by a competent electrician before it is used.
3
INTRODIJCTION
Heat transfer by simultaneous conduction and convection, whether free or forced,
forms the basis of most industrial heat exchangers and related equipment. The
measurement and prediction of heat transfer coefficients for such circumstances is
achieved in the Armfield apparatus by studying the temperature profiles and heat
flux in an air duct with associated flat and extended transfer surfaces. The vertical
duct is so constructed that the air temperature and velocity can be readily measured,
and a variety of /'plug-in" modules of heated solid surfaces of known dimensions
can be presented to the air stream for detailed study. A fan situated at the top of the
duct provides the air stream for forced convection experiments.
An independent bench mounted console contains temperature measurement, power
control, and fan speed control circuits with appropriate instrumentation.
Temperature measurement, to a resolution of 0.1'C is effected using thermistor
sensors with direct digital read-out in oc.
Air velocity is measured with a portable anemometer mounted on the duct.
The power control circuit provides a continuously variable, electrical output of 0-100
watts with a direct read-out in watts.
Using the instrumentation provided, free and forced convective heat transfer
characteristics may be determined for:1
A flat surface
.
An array of cylinders (pinned heat sink) A@n
2
array of fins (finned heat sink)
.
3Each module may be used independently on the bench, to demonstrate free
.convection in a horizontal mode.
The apparatus is fully self-contained
5
I
RECE:-IPT OF EQUIPMENT
I
SALES IN THE LINITED KINGDOM
The a- paratus should be carefully unpacked and the components checked .P
again-it the Advice Note. A copy of the Advice Note is supplied with this instruction
manual for reference.
Any omissions or breakages should be notified to Armfield Ltd within three,days of
receipt.
SALES OVERSEAS
The apparatus should be carefully unpacked and the components checked
against the Advice Note. A copy of the Advice Note is supplied with this
instruction manual for reference.
Any c)missions or breakages should be notified immediately to the Insurance Agent
stated on the Insurance Certificate if the goods were insured by Armfield Ltd.
Your own insurers should be notified immediately if insurance was arranged by
yourselves.
6
DESCRIPTION
Ali numerical references relate to the diagram on page 9.
The apparatus consists of a vertical rectangular duct supported by a bench mounted
stand (1). A flat plate (3) pinned (4) or finned (5) exchanger may bE! installed in the
duct and secured by a quick-release catch (18) on each side. Each exchanger
incorporates an electric heating element
with thermostatic protection against
overheating. The temperature at the
base of each exchanger is monitored by a
thermistor sensor (19)
with connecting lead (7).
The exchanger in use may be viewed through an acrylic window (14) in the wall of
the duct.
A@n upward flow of air may be generated in the duct with a variable speed fan (21)
mounted at the top.
A:ir velocity in the duct, whether natural or forced, is indicated on a portable
anemometer (2) held in a bracket (15) on the duct wall. The anemometer sensor (16)
is inserted through the wall of the duct.
A therrnistor probe (6) permits measurement of the in-going and out- going air
temperatures together with surface temperatures of exchanger pins and fins.
These temperatures are determined by inserting the probe through access holes (20)
in the duct wall.
An electric console (8) incorporates a variable auto-transformer with a digital
readout to control and indicate power supplied to the exchanger on test. The
exchanger is connected to a terminal box (11) mounted on the vertical duct which in
turn is connected to the console via the supply lead (10). A variable low voltage DC
supply is provided for the fan via the supply lead (17). A digital readout indicates
the temperature using a therrnistor probe connected to a flexible lead (6).
Power is supplied to the equipment via a supply lead (9) connected to the rear
of the console.
INSTALLATION
REQUIREMENTS
ELECTROMAGNETIC COMPATIBILITY
This apparatus is classified as Education and Training Equipment under the
Electromagnetic Compatibility (Amendment) Regulations 1994. Use of the
apparatus outside the classroom, laboratory or similar such place invalidates
conformity with the protection requirements of the Electromagnetic Compatibility
Directive (89/336/EEC) and could lead to prosecution.
FACILMES REQUIRED
The equipment should be installed on a firm, level work surface. A single phase
electrical supply will be required.
No other services are necessary.
10
CONNE(@PTION TO SERVICES
ELECTRICAL SUPPLY FOR VERSION HT6-A
The equipment requires connection to a single phase, fused electrical supply. The
standard electrical supply for this equipment is 220/24OV, 5OHz. Check that the
voltage and frequency of the electrical supply agree with the label attached to the
supply cable on the equipment. Connection should b(? made to the supply cable as
follows:EARTH
LIVE (HOT)
NEUTRAL I
AMP
GREEN/YELLOW BROWN
BLUE
Fuse Rating
ELECTRICAL SUPPLY FOR VERSION HT6-B:
The equipment requires connection to a single phase, fused electrical supply. The
standard electrical supply for thi@- equipment is 12OV, 6OHz. Check that the
voltage and frequency of the electrical supply agree with the label attached to the
supply cable on the equipment. Connection should be made to,the supply cable as
follows:EARTH LIVE
(HOT)
NEUTRAL 2
AM]?
GREEN/YELLOW BROWN
BLUE
Fuse Rating
ELECTRI'CAL SUPPLY FOR VERSION HT6-G,
The equipment requires connection to a single phase, fused electrical supply. 'The
standard electrical supply for this equipment is ??0/24OV, 6OHz. Check that the
voltage and frequency of the electrical supply agree with the label attached to the
supply cable on the equipment. Connection should be made to the supply cable as
follows:EARTH
LIVE (HOT)
NEUTRAL I
AMP
GREEN/YELLOW BROWN
BLUE
Fuse Rating
11
CONIMISSIONING
Having connected the apparatus to the electrical supply, (page 11) correct operation
should be checked as follows:Turn the heater power control (A) and fan speed control (B) fully anti- clockwise.
Connect the fan supply lead (17) at the base of the duct to the socket (C) beneath the
fan speed control on the instrument console.
Connect the thermistor probe lead (6) to the socket (D) beneath the temperature
meter on the instrument console.
Connect the heater supply lead (10) to the socket (E) beneath the power control knob
on the instrument console.
Clamp the flat plate heat exchanger (3) into the duct using the two toggle clamps (18)
and connect the supply lead to the socket on the cover.
Connect the exchanger temperature lead (7) to the socket (F) on the heat exchanger.
Install the four 'AA' Alkaline Manganese batteries in the anemometer (2) as shown
on the battery holder.
To check the condition of the batteries in the anemometer, set the switch to
'Velocity' and observe the battery low' LED. If the LED remains illuminated the
batteries should be changed before using the instrument.
To set the anemometer to the zero position, slide the protective cover forward over
the probe head to isolate it from any air movement. Set the switch to 'Velocity' and
adjust the knurled wheel marked 'Zero' until the pointer is aligned with the zero on
the scale.
Carefully slide the protective cover rearwards to expose the probe head then
locate the probe (16) into the bush fitted to the duct. Place the meter into the
bracket (15) situated on the side of the duct.
Ensure that the arrow on the tip of the probe is aligned with the direction of the
airflow when inserting the probe through the wall of the duct. Set the switch to 'off'
when the anernorneter is not being used.
Switch the equipment on by depressing the ON/OFF switch on the left hand side of
the console.
Check that the LED temperature meter and wattmeter are illuminated
12
Check that the temperature meter indicates ambient temperature.
Increase the heater power in the exchanger by rotating the power control knob
clockwise. The power supplied to the exchanger should be shown in watts on
the meter.
NOTE:
The wattmeter is calibrated to read in the range 0 to 99.9 watts.
Depending on the supply voltage it may be possible to exceed the
maximum reading on the wattmeter if the power control knob is turned
fully clockwise. This will not cause damage to the wattmeter but
readings in excess of 99.9 watts will commence again at 0 watts. As the
suggested experiments do not exceed 80 watts this characteristic will not
affect the operation of the equipment.
Switch on the fan and increase the speed by rotating the fan speed control knob (B)
clockwise.
Set the switch to 'Velocity' on the anemometer and observe that the air velocity is
indicated on the meter scale.
-TConnect the exchanger temperature lead (7) to the socket (D) on the console. Check
that the temperature meter indicates the increasing temperature of the heat exchanger
metalwork.
Set the heater power control knob and fan speed control knob to minimum (anticlockwise).
Set the ON/OFF switch on the console to the OFF position.
Commissioning of the equipment is now complete.
13
ROUTINE MAINTENANCE
To preserve the life and efficient operation of the equipment it is important
that the equipment is properly maintained. Regular servicing/maintenance of
the equipment is the responsibility of the end user and must be performed by
qualified personnel who understand the operation of the equipment.
In addition to regular maintenance the following notes should be observed:The equipment should be disconnected from the electrical supply when not in
use.
2.
The exterior of the equipment should be periodically cleaned. DO NOT use
abrasives or solvents.
T'he Digital Wattmeter is protected by a fuse which is located in a holder on the rear
panel of the electrical console. If replacement is necessary the fuse should be rated
250 niA, 20mm x 5mm, Quick Blow (F), ceramic.
15
INDEX 'rO EXPERIMENTS
Page No.
EXPERIMENT A
A-1
To demonstrate the relationship between power input and
surface temperature in free convection.
EXPERIMENT B
B-1
To demonstrate the relationship between power input and
surface temperature in forced convection.
EXPERIMENT C
C-1
To demonstrate the use of extended surfaces to improve heat
transfer from the surface.
EXPERIMENT D
-r-
D-1
To determine the temperature distribution along an
extended surface.
EXPERIMENT E
E-1
Comparison of a horizontal and vertical flat plate in free
convection.
16
EXPERIMENT A
OBJECT OF EXPERIMENT
To demonstrate the relationship
temperature in free convection.
between power input and surface
EQUIPMENTSET-UP.
SUMMARY OF THEORY.A heated surface dissipates heat primarily through a process called convection. Heat
is also dissipated by conduction and radiation, however these effects are not
considered in this experiment. Air in contact with the hot surface is heated by the
surface and rises due to a reduction in density. The heated air is replaced by cooler
air which is in turn heated by the surface and rises. This process is called free
convection.
The hotter the temperature of the surface, the greater the convective currents and the
more heat (power) will be dissipated.
If more power is supplied to a surface, the temperature of the surface must rise
to dissipate this power.
A-1
RF-ADINGS TO BE TAKEN.
Place the finned heat exchanger into the test duct. Record the ambient air
temperature (tA). Set the heater power control to 20 Watts. Allow sufficient time to
achieve steady state conditions before noting the heated plate temperature (tH).
Repeat this procedure at 40, 60 and 80 Watts.
RF-SULTS:
oc
Ambient air temperature (tA) =
Plot a graph of power against surface temperature (tH - tA).
T-@'PICAL--GRAPH OF POWER AGAINST SURFACE TEMPERATURE,
A-2
EXPEPIIMENT B
OBJECT OF EXPERIMENTTo demonstrate the relationship
temperature in forced convection.
between power input and surface
EQUIPMENT SET-UP:
SUMMARY OF THEORY.
In free convection the heat transfer rate from the surface is limited by the small
movements of air generated by this heat. More heat is transferred if the air velocity is
increased over the heated surface. This process of assisting the movement of air over
the heated surface is called Forced Convection. Therefore a heated surface
experiencing forced convection will have a lower surface temperature than that of
the same surface in free convection, for the same power input.
READINGS TO BE TAKEN.
Place the finned heat exchanger into the duct. Note the ambient (tH). Set the heater
power control to 50 Watts. Allow sufficient time to achieve steady state conditions
before noting the heated plate temperature (tH). Set the fan speed control to give a
reading of 0.5m/s on the thermal anemometer, allow sufficient time to achieve
steady state conditions. Record heated plate temperature. Repeat this procedure at
I.Om/s and I.Sm/s.
B-1
RESULTS:
Ambient air temperature (tH)
~
OC
Power input
~
Watts
Plot a graph of air velocity against temperature.
VELOCIT
Y
mIs
B-2
EXPERIMENT'
OBJECT OF EXPERIMENT.To demonstrate the use of extended surfaces to improve heat transfer from the
surface.
EQUIPMENT SET-UP.
Air
t ffovv
Fan
Tairnporature probe (t H)
~
Hext*r
Tomptratures
(tH, tA)
Heated Flat plate
test box
Temperature
Heater
Wattmeter I
powwor
(0)
-Tl-
proi3o ( t A )
control
a
I
010
11--
'
ON 'switch
r--=i
8 C3
I
I-
-q 0 --C
SUMMARY OF THEORY.
Heat transfer from an object can be improved by increasing the surface area in
contact with the air. In practice it may be difficult to increase the size of the body to
suit. In these circumstances the surface area in contact with the air may be increased
by adding fins or pins normal to the surface. These features are called extended
surfaces. A typical example is the use of fins on the cylinder and head of an air
cooled petrol engine. The effect of extended surfaces can be demonstrated by
comparing finned and pinned surfaces with a flat plate under the same conditions of
power input and air flow.
READINGS TO BE TAKEN.
Place the flat plate heat exchanger into the duct. Record the ambient air temperature
(tH). Set the heater power control to 75 Watts. Allow the temperature to rise to 80'C,
then adjust the heater power control to 20
C-1
Watts until a steady reading is obtained. Record heated plate temperature (tH). Set
the fan speed control to give Im/s using the thermal anemometer. Repeat this
procedure at 1.5 and 2.0m/s for the flat plate. Replace the flat plate with the finned
plate and repeat experiment. Replace the finned plate with the pinned plate and
repeat experiment.
RESULTS:
Ambient air temperature =
Input power
0c
= 20
Watts
Plot graphs of velocity against temperature for each of the plates.
Comment on the correlation between total surface area of the heat exchanger
and the temperature achieved.
FURTHER EXPERIMENTS:
Increase power input and repeat experiments.
C-2
--r-
EXPERIMENT D
OBJECT OF EXPEPIMENT
To determine the temperature distribution along an extended surface
EQUIPMENT SET-UP.
SUMMARY OF THEORY.
For a heat exchanger to be 100% efficient the complete extended surface
temperature must be the same as the back plate. In practice however this does not
occur because heat must flow along a pin or fin by conduction, which causes a
temperature gradient to occur. The steeper the gradient the less efficient the heat
exchanger. The efficiency however must not be confused with surface area e.g.
comparing pinned and finned. In reality the pin is more efficient, but in this
particular case the fin is marginally more efficient because of its surface area.
READINGS TO BE TAKEN.
Measure from the back plate the distances of the three access holes on the pinned
and finned heat exchangers. Place the pinned heat exchanger into the duct. Note the
ambient air temperature (tA). Set the heater power control to 60 Watts. Allow
sufficient time to achieve steady state conditions before noting the heated plate
temperature (tH). Insert the anemometer probe into the duct through the hole nearest
the heated plate ensuring that the tip of the probe is in contact with the pin. A small
D-1
amount of heat conducting compound on the tip will ensure a good thermal contact.
Note this temperature (tl). Record the pin temperatures (t2 and t3) using the
remaining two holes. Repeat this procedure at I-Om/s and 2m/s.
Remove the pinned heat exchanger and replace with the finned heat exchanger.
Repeat complete experiment.
PESULTS:
Ambient air temperature (tH)
~
Power input
~
Watts
Distance of nearest hole
~
mm
Distance of middle hole
~
mm
Distance of farthest hole
~
mm
Air velocity m/s
ti
-oc
Temperature 'C
t2 I t3
t4
0
1
2
Plot graphs of surface temperature against distance from back plate for the two heat
exchangers at various air velocities.
D-2
oc
For a heat exchanger to be 100% efficient, the whole of the extended surface must be
at the same temperature as the backplane.
In practice, this cannot occur because the flow of heat along the pins or fins by
conduction causes a temperature gradient to occur. The greater this gradient, the less
efficient the heat exchanger will be.
The efficiency of the heat exchanger must not be confused with the effect of a
change in surface area. For example, if the pinned and finned heat exchangers
supplied with the equipment are compared, the pin is more efficient than the fin
(slightly smaller temperature gradient) but the finned exchanger has a significantly
larger surface area than the pinned exchanger and can dissipate more heat for the
same surface temperature.
D-3
EXPERIMENT E
OBJECT OF EXPERIMENT.
Comparison of a horizontal and vertical flat plate in free convection.
EQUIPMENTSET-UP.
SUMMARY OF THEORY.
When a temperature difference is established between a wall and a stationary fluid,
the fluid adjacent to the wall will move upward if the wall temperature is higher than
that of the fluid, and downward if the wall temperature is lower. Density gradients
are set up in the fluid resulting in buoyancy forces and free convective currents. The
rate of heat transfer depends mainly on the fluid motion. The orientation of the plate
affects this movement of air. A horizontal plate restricts the movement of air and
reduces the heat transfer. The same plate mounted vertically will give improved heat
transfer.
READINGS TO BE TAKEN.
NOTE:
The wattmeter is calibrated to read in the range 0 to 99.9 watts.
Depending on the supply voltage it may be possible to exceed the
maximum reading on the wattmeter if the power control knob is turned
fully clockwise. This will not cause damage to the
E-1
wattmeter but readings in excess of 99.9 watts will commence again at 0
watts.
Place the flat plate exchanger horizontally onto a suitable surface. Record the
ambient air temperature (tA). Set the heater power control to 15 Watts. The surface
temperature of the flat plate (tH) can be recorded using the temperature probe, the
tip of the probe being held in contact with the surface by hand. To ensure good
contact the thermal compound should b used. Allow sufficient time to achieve
steady state conditions before noting the heated plate temperature. The plate
temperature should be taken at the centre of the plate. Place the flat plate vertically
taking care not to touch the heated surface with your hands. Repeat the experiment.
PESULTS.
Ambient air temperature (tA)
~
Input power
= 15
oc
Heater Temt) (tH) 'C
Watts
tfi - ta-gc-
Horizontal
Vertical
Comment on the effects of plate orientation on surface temperature.
E-2
GENERAL SAFETY RULES
I
Follow Pelevant Instructions
a
Before attempting to install, commission or operate equipment, all
relevant suppliers'/manufacturers' instructions and local
regulations should be understood and implemented.
It is irresponsible and dangerous to misuse equipment or ignore
instructions, regulations or warnings.
Do not exceed specified maximum operating conditions (eg.
temperature, pressure, speed etc.-
b
c
2
a
b
c
d
e
f
Installatio
n
Use lifting tackle where possible to install heavy equipment. Where manual
lifting is necessary beware of strained backs and crushed toes. Get help from
an assistant if necessary. Wear safety shoes where appropriate.
Extreme care shc@uld be exercised to avoid damage to the equipment during
handling and unpacking. When using slings to lift equipment, ensure that the
slings are attached to structural framework and do not foul adjacent
pipework, glassware etc. When using fork lift trucks, position the forks
beneath structural framework ensuring that the forks do not foul adjacent
pipework, glassware etc. Damage may go unseen during commissioning
creating a potential hazard to subsequent operators.
Where special foundations are required follow the instructions provided and
do not improvise. Locate heavy equipment at low level.
Equipment involving inflammable or corrosive liquids should be sited in a
containment area or bund with a capacity 50% greater than the maximum
equipment contents.
Ensure that all services are compatible with the equipment and that
independent isolators are always provided and labelled. Use reliable
connections in all instances, do not improvise.
Ensure that all equipment is reliably earthed and connected to an electrical
supply at the correct voltage. The electrical supply must incorporate a
Residual Current Device (RCD) (alternatively called an Earth Leakage
Circuit Breaker - ELCB) to protect the operator from severe electric shock in
the event of misuse or accident.
Potential hazards should always be the first consideration when deciding on a
suitable location for equipment. Leave sufficient space between equipment
and between walls and equipment.
9
a
3
Commissioning
a
Ensure that equipment is commissioned and checked by competent membera
of staff before permitting students to operate it.
4
Operation
a
Ensure that students are fully aware of the potential hazards when operating
equipment.
Students should be supervised by a competent member of staff at all times
when in the laboratory. No one should operate equipment alone. Do not leave
equipment running unattended.
Do not allow students to derive their own experimental procedures unless
they are competent to do so.
Serious injury can result from touching apparently stationary equipment when
using a stroboscope to 'freeze' rotary motion.
b
c
d
5
Maintenance
a
Badly maintained equipment is a potential hazard. Ensure that a competent
member of staff is responsible for organising maintenance and repairs on a
planned basis.
Do not permit faulty equipment to be operated. Ensure that repairs are
carried out competently and checked before students are permitted to operate
the equipment.
-r--
b
6
Using Electricity
a
At least once each month, check that ELCB's (RCCB's) are operating
correctly by pressing the TEST button. The circuit breaker must trip when
the button is pressed (failure to trip means that the operator is not protected
and a repair must be effected by a competent electrician before the equipment
or electrical supply is used).
Electricity is the commonest cause of accidents in the laboratory. Ensure
that all members of staff and students respect it.
Ensure that the electrical supply has been disconnected from the equipment
before attempting repairs or adjustments.
Water and electricity are not compatible and can cause serious injury if they
come into contact. Never operate portable electric appliances adjacent to
equipment involving water unless some form of constraint or barrier is
incorporated to prevent accidental contact.
Always disconnect equipment from the electrical supply when not in use.
b
c
d
e
b
7
Avoiding fires or explosion
a
9
Ensure that the laboratory is provided with adequate fire extinguishers
appropriate-to the potential hazards.
Where inflammable liquids are used, smoking must be forbidden. Notices
should be displayed to enforce this.
Beware since fine powders or dust can spontaneously ignite under certain
conditions. Empty vessels having contained inflammable liquids can contain
vapour and explode if ignited.
Bulk quantities of inflammable liquids should be stored outside the laboratory
in accordance with local regulations.
Storage tanks on equipment should not be overfilled. All spillages should be
immediately cleaned up, carefully disposing of any contaminated cloths etc.
Beware of slippery floors.
When liquids giving off inflammable vapours are handled in the laboratory,
the area should be ventilated by an ex-proof extraction system. Vents on the
equipment should be connected to the extraction system.
Students should notbe allowed to prepare mixtures for analysis or other
purpose without competent supervision.
8
Handling poisons, corrosive or toxic materials
a
e
Certain liquids essential to the operation of equipment, for example mercury,
are poisonous or can give off poisonous vapours. Wear appropriate protective
clothing when handling such substances. Clean up any spillage immediately
and ventilate areas thoroughly using extraction equipment. Beware of
slippery floors.
Do not allow food to be brought into or consumed in the laboratory. Never
use chemical beakers as drinking vessels.
Where poisonous vapours are involved, smoking must be forbidden. Notices
should be displayed to enforce this.
Poisons and very toxic materials must be kept in a locked cupboard or store
and checked regularly. Use of such substances should be supervised.
When diluting concentrated acids and alkalis, the acid or alkali should be
added slowly to water while stirring. The reverse should never be attempted.
9
Avoiding cuts and bums
a
Take care when handling sharp edged components. Do not exert undue force
on glass or fragile items. '
Hot surfaces cannot, in most cases, be totally shielded and can produce severe
burns even when not 'visibly hot'. Use common sense and think which parts of
the equipment are likely to be hot.
b
c
d
e
f
b
c
d
b
c
10
Eye protection
a
Goggles must be worn whenever there is a risk to the eyes. Risk may arise
from powders, liquid splashes, vapours or splinters. Beware of debris from
fast moving air streams. Alkaline solutions are particularly dangerous to the
eyes.
Never look directly at a strong source of light such as a laser or Xenon arc
lamp. Ensure that equipment using such a source is positioned so that
passersby cannot accidentally view the source or reflected ray.
Facilities for eye irrigation should always be available.
b
c
11
Ear protection
a
Ear protectors must be wom when operating noisy equipment.
12
Clothing
a
Suitable clothing should be wom in the laboratory. Loose garments can cause
serious injury if caught in rotating machinery. Ties, rings on fingers etc.
should be removed in these situations.
Additional protective clothing should be available for all members of staff and
students as appropriate.
b
13
Guards and safety devices
a
Guards and safety devices are installed on equipment to protect the operator.
The equipment must not be operated with such devices removed.
Safety valves, cut-outs or other safety devices will have been set to protect the
equipment. Interference with these devices may create a potential hazard.
It is not possible to guard the operator against all contingencies. Use common
sense at all times when in the laboratory.
Before starting a rotating machine, make sure staff are aware how to stop it in
an emergency.
Ensure that speed control devices are always set at zero before starting
equipment.
b
c
d
e
14
First aid
a
If an accident does occur in the laboratory it is essential that first aid
equipment is available and that the supervisor knows how to use it. A
notice giving details of a proficient first-aider should be prominently
displayed.
A 'short list' of the antidotes for the chemicals used in a particular
laboratory should be prominently displayed.
b
c
d