UNIT 12 FIRE HAZARDS
Structure
12.1 lntroduction
Objectives
12.2 Fire Hazards in the Laboratory
The Firt Tria~igle
Causes of Fires
Classification of Fires
12.3 Precautions for Fire Preventioi~
Fire Alarms
Fire Escapes
Fire Barriers
12.4 Extinguishing a Fire
Fire Exting~~ishers
Use of Fire Extinguishers
12.5 Summary
12.6 Terminal Questions
12.7 Answers
12.1 INTRODUCTION
In the first unit of this block you read about hazards due to electricity and gases
in the science laboratories. 'The second unit deals with yet another type of
common hazard which is because of fire. The consequences of fire are well
known; still many do not take enough precautions and preventive measures.
According to National Crime Record Bureau, the number of deaths in our
country due to fire accidei~tsduring 1994 and 1995 are 23050 and 21226,
respectively. The person-in-charge of any laboratory should have a knowledge
to handle a fire hazard. In case the fire spreads beyond control, the laboratory
staff should know how to call the fire brigade, raise the alarm and ask for other
help. In this unit, you will learn about the major causes of fire, its
classification, precautions and prevention. You will also learn about the fire
extinguishers. The next unit deals with hazards in handling chemical and
radioactive materials.
Objectives
After studying this unit you should be able to:
explain the significance of the fire triangle,
list common causes of fire,
describe the purpose and use of fire alarms, escapes and barriers,
classify different types of fires,
list the main types of fire extinguishers,
describe the use of different types of fire extinguishers, and
describe how to use a fire blanket and the purpose of the buckets.
12.2 FIRE HAZARDS IN THE LABORATORY
The average science laboratory is a particularly hazardous area when it comes
to fire. Flammable liquids, compressed and liquefied gases, hazardous and
Hazards in Laboratories reactive materials, are all either in use or in store in the laboratory. In addition,
there are many sources of ignition available. Before you learn about the major
causes of fire, let us see in the following subsection the factors that are required
for fire to burn.
12.2.1 The Fire Triangle
Generally, a fire needs three things to burn:
Fuel - something to bum, e.g.oi1.
Oxygen - to maintain combustion.
Ignition - something to start the fire, e.g. excessive heat, electrical spark, etc.
This principle can be depicted in the form of a triangle as shown in Fig. 12.1.
Fig.lZ.1: The fire triangle.
By removing any one of the three sides of the triangle, fire is prevented. For
example, many fires obtain oxygen from the air where it is about 20% by
volume. Fire extinguishers, e.g. sand or foam (subsection 12.4.2), prevent
oxygen being available to the fuel or ignition source. Although air is the most
common source of oxygen, other sources are,
chlorates
permanganates
nitrates
peroxides
dichromates
other oxidising agents
The essence of fire prevention is to prevent the formation of fire triangle.
With air containing oxygen all around us, this consists primarily of keeping
fuel and ignition sources apart.
12.2.2 Causes of Fire
The potential fire risk arises from the presence of combustible solids, liquids or
gases in conjunction with ignition sources. One or more class is generally
found in most laboratories.
The 10 commonest causes of accidental fire are:
i) Smoking materials (matches, cigarettes, etc.)
ii) Misusedlfaulty electrical installations
iii) Mechanically produced heat or sparks
iv) Naked lights
v) Oxyacetylene equipment
vi) Malicious or intentional ignition
vii) Children at play Fire Hazards
viii) Gas installations
ix) Oil installations
x) Rubbish burning
And the most likely fuel sources for accidental fires are: Flammable means the
Waste and rubbish same as inflammable, i.e.
likely to catch fire and
Packing and wrapping materials their opposites are non-
Flammable liquids flammable and non-
Electrical insulation materials inflammable. Because
"inflammable" has often
Fires are sometimes caused by the 'magnifying glass' effect of bottles and been confused with "non-
flammable", the word
spherical flasks filled with liquid and standing in the direct rays of the sun. "inflammable" is hardly
used. We recommend
Now try to do the following SAQ and check for the answer at the end of this that you keep to current
unit. usage, i.e. "flammable"
and "non-flammable".
SAQ 1
Suppose there is a beaker containing a flammable solvent and it catches fire.
Keeping in mind the fire triangle, can you suggest a way this fire can be
extinguished ?
12.2.3 Classification of Fires
As explained in subsection 12.2.2 also. we can say that the four main sources of
fire risk in the science laboratory are:
i) flammable substances,
ii) compressed and liquefied gases,
iii) hazardous materials and reactions, and
iv) the availability of sources of ignition.
It is standard international practice to classify the main sources of fire
according to their nature. In many directions and instructions on fire fighting
equipment, a fire classification code is generally used to describe certain types
of fires. The classification is summarised in the table given below.
Table 12.1: Classification of fires.
Class Type or nature of fire
of fire
A Fires involving materials which contain carbon, e.g. wood, cloth, paper, rubber.
5 Fires involving flammable liquids, e.g, petrol, oil, alcohol and many other organic
solvents.
I C
D
I Fires involving flammable gases, e.g. methane, propane, hydrogen, ethyne
(acetylene) and butane.
Fires involving flammable metals, e.g. sodium, potassium, calcium, magnesium
and other combustible metals or their hydrides.
E I Electricity and electrical appliances. J
.-
Hazards in Laboratories After getting familiar with the general causes and types of fires, you will study
in the next section about the precautions to be taken to prevent any type of fire.
Before proceeding to next section, try to answer the following SAQ.
SAQ 2
"The application of heat is needed in a large amount of scientific work and the
Bunsen burner is the cheapest and most efficient way of supplying heat to any
point in the science laboratory. For all its advantages, though, the Bunsen
burner is a fire risk".
Write down, in a few words only, any points you can think of that could justify
this statement.
12.3 PRECAUTIONS FOR FIRE PREVENTION
Legal regulations In the event of fire or explosion occurring there should be a prearranged plan of
regarding fire are the necessary action to be taken. All personnel must be made aware of this and
discussed in Sec. 17.6 fire drill should be carried out at least twice a year in order to familiarise staff
of Unit 17. with these procedures. The essential procedures generally to be followed by
the laboratory staff are explained in the following subsections.
12.3.1 Fire Alarms
Most modern fire alarm systems are electric and can be activated from several
points throughout a building. These points usually consist of glass-covered
switches which should be painted red and sited no more than 30 metres apart.
Some sophisticated systems integrate alarm buttons with a smoke detector
system, and it is usual for a complete ban on smoking to be enforced in a
building protected by a smoke detector system. The fire brigade should be
called in case there is a need. The person-in-charge should be trained to assess
the severity in case of an outbreak of fire and act accordingly.
12.3.2 Fire Escapes
When a fire breaks out in a building, it is not unusual for people to panic.
Sometimes flames can spread rapidly, especially if fanned by blow of air from
open or broken windows and doors, and blinding and choking smoke can soon
envelop clear spaces. In such circumstances it is essential that escape routes
are well known, clearly indicated and free from obstruction. Suitable escape
routes are not susceptible to blockage or failure in emergencies. Similarly
alarm points and assembly areas must be well indicated and accessible.
12.3.2 Fire Barriers
When a fire starts in a building it spreads quickly by:
a) Radiation - Intense heat radiates to neighbouring surfaces which are
rapidly heated to ignition point. ~ a t e i i a l themselves
s then ignite or when
heated give off flammable gases and vapours.
b) Convection - Flames and hot gases rise by convection increasing the Fire Hazards
effects of radiation and burning the surfaces they touch. Thus ceilings
quickly ignite and staircases and lift shafts often become quickest ways of
spreading a fire.
The spread of fire can be limited by cornpartmentalising the interior of a
building with fire barriers such as
fire doors
fire retardant walls
fire resistant floors
Fire doors are fitted with self -closing hinges and are always hung so as to Most people who die in
open outwards towards the fire exit. They act in two additional ways in fire accidental fires, die not
prevention from burning but from
asphyxiation or
i) they restrict oxygen supply to the fire. poisoning from the
ii) they act as smoke barriers. fumes and smoke emitted
by fire.
Fire doors should always be kept closed and should never be obstructed.
SAQ 3
Lifts should not be used as fire escapes. Why do you think so?
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We know that inspite of precautions taken at the work place there may be a fire
outbreak. In such cases, the person-in-charge should know the use of fire
extinguishers. In the next section we will study different types of fire
extinguishers and their use.
12.4 EXTINGUISHING A FIRE .
The techniques and equipment which you will learn about in this section relate
to the standard kinds of fire fighting equipment found in buildings open to the
public. This equipment is meant only to contain and extinguish small fires and
is a first-aid fire fighting measure only. .It does not in any way turn the user
into a fireman. If for some reason you were unable to contain or extinguish a
fire immediately, you would be well advised to evacuate the building and await
the arrival of the fire brigade who are better able to control fire.
It is difficult for you to judge when it is best to desert the fire. Obviously if
you've exhausted your extinguisher and 'the fire is still raging, it would be time
to go. If you are using a fire hose, the decision is harder to make. Just
remember that lives can easily be lost in an effort to rescue an over-zealous but
unwise amateur fireman! Let us give a look at the different types of fire
extinguishers in the next subsection.
1 Hazards in Laboratories 12.4.1 Fire extinguishers
You would recall the classification of fires dealt in subsection 12.2.3. Table
12.2 summaries the type of extinguisher used for different classes of fire.
Table 12.2: Summary of fire extinguishers for different types of fire.
Extinguisher
Water
coz
Foam
Vapourising liquids:
Halon is a halogenated CC14 (carbon tetrachloride)
hydrocarbon used as an BCF (bromochlorodifluoro
extinguishing medium. methane-halon)
Dry powder
Dry sand
1 Fire blanket
Based on this unit, two
activities are included in
This table as you can see only shows which type of fire extinguisher is to be
Exercise 1 1 of Block 5 used for what class of fire. However the laboratory staff should be trained to
dealing with the practical make use of fire extinguishers for different situations. Let us study this in the
component of this next subsection. Before that try to answer the following SAQ.
course.
SAQ 4
Using the list given in (a) below, state the name of appropriate fire
extinguishers for each of the fires mentioned in (b).
(a) sand, carbon dioxide, fire blanket and water
(b) i) fire involving flammable liquids and organic solvents ..................
ii) fire because of burning clothing ..................
iii) fire involving carbonaceous materials ..................
iv) fire because of flammable and combustible metals ..................
12.4.2 Use of Fire Extinguishers
We know that one type of fire extinguisher cannot serve the purpose on all
kinds of fire. In this subsection you will study about the use of different types
of fire extinguishers, fire buckets and fire blankets. How would you use a foam
extinguisher, for instance? Would you just point it at a fire and force a jet of
the extinguishing agent? Would you do the same with a water extinguisher or a
carbon dioxide extinguisher?
There's no simple answer to any of these questions, but there is a technique to Fire Hazards
be learnt for each type of extinguisher. In the same way that you would use
certain kinds of fire extinguisher for certain kinds of fire, you would use an
appropriate technique for each kind of fire extinguisher. To do otherwise
would be wasting valuable resources, probably at a time when these resources
are most needed. The difference between knowing what fire extinguisher to
use and how to use it, and not knowing this information could be the difference
between life and death for someone. However, remember that fire
extinguishers are usually suitable only for small fires.
Use the following procedure for fire fighting.
(1) Always take a position between the fire and the exit so your escape route
cannot be cut off. Fire extinguishers should always be placed close to
doors and other exits for this reason.
(2) Do not continue to fight a fire if it is dangerous to do so or if there is a
possibility that your escape route may be cut off by fire or smoke. A
potentially fatal asphyxiating concentration of carbon dioxide can build
up quickly if C 0 2 extinguishers are operated in an enclosed space.
(3) If you have to withdraw, close doors or windows behind you, wherever
possible.
The recommended procedures for operating the different types of fire
extinguishers are given below.
(a) Water extinguishers
Direct the jet at the base of the flame and keep it moving across the fire.
Attack a fire which is spreading vertically at its lowest point and follow the fire
upwards. Concentrate the jet on any hot spots once the main fire is
extinguished.
(b) Carbon dioxide, dry powder and vapourising liquid extinguishers
Fires produced by spilled liquids should be extinguished by directing the jet or
discharge horn towards the near edge of the fire and with a rapid sweeping
motion drive the fire towards the far edge until all the flames are extinguished
(Fig. 12.2). Other types of fire may be extinguished by directing the jet directly
at the burning material. The current should be switched off first if the fire is
close to electrical equipment. The controlled discharge type of extinguisher
may be turned off once the fire is out, but the fire should not be left unattended
as re-ignition may occur. Vapourising liquid extinguishers should not be used
in a confined space if there is a danger that the fumes may be inhaled.
I
Fig.12.2: Use of carbon dioxide and vapourising liquid extinguishers.
Hazards in Laboratories A fire blanket may be used in conjunction with a carbon dioxide extinguisher,
for example, for flammable liquids and other fires. The fire is first smothered
with the blanket and the carbon dioxide extinguisher is used to ensure that all
Glass fibre is less than a the flames are extinguished. Burning clothing should be extinguished by
quarter of a micrometer in rolling the victim in the fire blanket on the floor. Fire blankets are more
diameter, that is woven into
a cloth and impregnated usually made of glass fibre than of asbestos. You will study more about fire
with various resins. blankets shortly. You will learn to use a carbon dioxide fire extinguisher in
Exercise 11 of Block 5 of this course.
Asbestos is a type of fibrous
silicate mineral, mainly
(c) Foam extinguishers
calcium magnesium silicate.
It is used as a heat insulating
material and for fire proof
If the burning liquid is in a container the jet should be directed at the inside
fabrics. edge of the vessel or at a vertical surface in order to break the jet and allow the
foam to build up and spread across the surface of the liquid (Fig. 12.3). If this
is not possible, the correct procedure is to stand well back (perhaps as far as 6
or 7 m) and to direct the jet with a gentle sweeping movement to allow the
foam to drop down and form a layer on the surface of the liquid (Fig. 12.4). Do
not aim the jet directly into the liquid as this will drive the foam under the
surface where it will be ineffective in extinguishing the fire and may spread the
fire by splashing the liquid on the surroundings.
Fig. 12.3: Use of foam extinguisher-I. Fig.12.4: Use of foam extinguisher-11.
(d) Fire Buckets
All labs should be equipped with a fire bucket. The buckets are not used only
for carrying water to a fire. This is one of their uses. The other way a fire
bucket is used is by keeping it filled with sand and a scoop. You will find that
sand can extinguish fire quickly and effectively. It is particularly useful for
dealing with liquid spillage or with reactive chemicals such as alkali metals.
Other advantages of sand are that it is easy to use and it is easy to clear up.
If you use sand as an extinguisher or absorber, use it liberally. Speed is
important when controlling fire or dangerous spillage, but you must be careful
not to throw a large quantity of sand onto the hazard in your haste. This could
cause splashing which would make the hazard worse. Of course, sprinkling too
little sand onto the hazard is equally useless. Quick, liberal pouring is the best
method and you should aim to cover the whole area of the flames or spillage,
working from the outer edge inwards. Sand buckets should be three-quarters
full, and covered with a loose cardboard disc with a hole in the centre. This
sand should not be used for sand baths.
(e) Fire Blankets
We have already discussed the use of fire blankets, but it is worth noting that
fire blankets are now made of glass fibre instead of asbestos, and that they are
I usually installed in conjunction with another type of extinguisher. The
important points when using a fire blanket are to ensure that the blanket is:
1) spread out as much as possible.
Fire Hazards
2) laid as flat as possible on the burning surface.
Remember the following in case of using fire blanket for extinguishing fire on
someone's clothes:
You must hold the blanket with the tapes wide apart.
Knuckle: The joint
The bottom edge must trail on the ground. connecting a finger to the
You must hold the blanket so that it protects your fingers from the flames, rest of the hand.
e.g. in clenched fists so that it hangs over your knuckles and forearms.
You must wrap your arms around the casualty and pull him to the ground Forearms: The part of the
to avoid flames reaching the face and hair. arm between elbow and
b wrist.
SAQ 5
I
Tick (4)mark the correct answerls. When using a foam fire extinguisher, do
YOU
i) direct the jet at the base of the flame ?
ii) direct the jet at a surface adjacent to the flame to break the jet and allow
the foam to settle on the burning surface ?
iii) project foam so that it falls on to the surface from a distance ?
iv) hold the extinguisher upside down ?
12.5 SUMMARY
Let us recall briefly what all we have learnt about fire hazards in this unit. Fire
accident can happen due .to a number of reasons, like, flammable liquids, faulty
electrical and gas installations, etc. Three factors, fuel, ignition and oxygen are
essential for fire to take place. Therefore, it is advisable to control at least one
of these to prevent fire hazard.
The fires are classified into five main categories depending upon their nature.
The laboratory incharge should be aware of all precautioning procedures like
fire alarms, fire escapes, fire barriers etc, in case of an outbreak of fire. The
staff should be trained in using different types of fire extinguishing devices
like, fire extinguishers, blankets, buckets, etc. The laboratory staff should be
able to judge the class of fire and act accordingly. This will help in preventing
any casualty in the work place.
12.6 TERMINAL QUESTIONS
1. Imagine that the fire alarm has sounded, smoke is coming through the far
end of the lab, and you are waiting for the last few people to come out of
the lab. This gives you about ten seconds in which to perform one last
task before leaving the lab door. Would you
i) pack as many of your notes and belongings as possible into a brief
case and carry them out?
ii) find any fire extinguishers you can and take them with you?
iii) close all windows?
iv) put your lab coat on ?
Choose the correct answer and explain.
Hazards in Laboratories 2. Wedging the door open is common practice in hot, stuffy weather, or
when some particularly distasteful smell dominates the atmosphere. If
the lab door is a fire door, do you think that wedging it open is
justifiable? Briefly, write down reasons to support your judgement.
3. Bearing in mind the fire triangle, briefly state the principle behind the use
of sand as an extinguisher and state for what type of fire can sand be used
for.
4. Write down at least two examples for each of the following type of fire
risk.
i) carbonaceous materials iii) hazardous materials
ii) flammable liquids iv) sources of ignition
5. What are the three general principles for fire-fighting'?
1
12.7 ANSWERS
Self-assessment Questions
1. The fire can be extinguished by putting a cover on the beaker and cutting
off the supply of oxygen.
2. The burner is a fire risk because of
i) its naked flame and proximity to fuel sources.
ii) difficulty in seeing whether the burner is on or off because of its
invisible flame.
iii) the gas from the burner may leak and get ignited by a source of
ignition.
3. Lifts are not to be used as fire escapes because a fire may cause electrical
failure and jam the lift. Also the lift shaft is likely to fill with smoke and
fumes.
4. i) carbon dioxide iii) water
ii) fire blanket iv) sand
5. ii) and iii). Remember that the principle behind the foam extinguisher is
to blanket the flames with a layer of foam. Method i) would not achieve
this but would probably spread the fire. Method (iv) does not apply to
modern extinguishers at all.
Terminal Questions
1. iii), Closing windows cuts off the oxygen supply in the same way as fire
doors and thus helps to reduce the spread of the fire.
2. It is definitely a bad idea. This action defeats the main objects of a fire
which are:
i) to present a flame barrier to any fire,
ii) to limit the oxygen supply to a fire by stopping air flow, and
iii) to contain fumes and smoke.
3. Application of sand deprives a fire of oxygen (or its supporting medium )
and prevents combustion. Sand is suitable for all types of small fires
particularly those involving alkali metals.
4. i) wood, paper, timber iii) sodium, potassium
ii) petrol, benzene, alcohol iv) excessive heat, sparks
5. i) Always position yourself between the fire and an exit.
ii) Do not continue to fight a fire if it is dangerous to do so or your
escape route is likely to be cut off by fire or smoke.
iii) Where possible, close all doors and windows if you have to
withdraw.
