CHAPTER THREE: FIRE, FIREFIGHTING AND FLAMES  
A. FIRE  
Fire is a state at which ignited material combines with oxygen and gives off light,  
heat and flame and combustion products.  
When controlled, fire can be beneficial and used for cooking, heating or industrial  
processes.  
COMPONENTS NEEDED TO START A FIRE (FIRE TRIANGLE)  
Three things are needed to start fire are: (i) Fuel (ii) Oxygen (iii) Heat energy  
These three components are known as fire triangle as seen in diagram below.  
If any of the three components is missing no fire will start or continue burning.  
For a fire to start a combination of heat, oxygen and fuel is needed in the suitable  
proportions.  
(i) Fuel: is a substance that releases energy when burning. Examples; petrol, diesel,  
kerosene, charcoal, fire wood, coal, natural gas etc.  
(ii) Oxygen (air): Oxygen supports combustion. A fuel will only burn if there is  
sufficient supply of oxygen.  
Combustion is the process of burning a substance in the presence of oxygen.  
(iii) Heat: Heat is the thermal energy transferred from a hotter object (system) to a  
cooler system that are in contact. For a fire to start, the temperature should be at  
the kindling point of that fuel or above it. Every fuel has its own kindling point.  
Below the kindling point, the fuel will not catch fire.  
B. FIREFIGHTING  
Firefighting is the act of extinguishing of harmful fires and mitigating (reducing)  
their effects.  
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Uncontrolled fires can be dangerous and destructive leading to injuries, property  
damage and environmental harm.  
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Materials which are used to put out fires are called Fire extinguishers.  
Firefighting involves eliminating at least one of the three components in the fire  
triangle.  
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Most firefighting equipment work by cutting off the oxygen supply to the fire to  
extinguish it effectively.  
CLASSIFICATION OF FIRES  
To extinguish fire, one must know which class of fire is it. Fires are classified  
according to the burning materials. Use of wrong extinguisher may result in the  
spreading of fire.  
Fires are classified based on the type of burning materials. There are five classes of  
fire which are  
(i) Class A fires  
(ii) Class B fires (iii) Class C fires (iv) Class D fires (v) Class F fires  
CLASS BURNING MATERIAL  
APPROPRIATE EXTINGUISHERS  
(i) Use water.  
Ordinary SOLID combustible  
A
B
(ii) Any type of portable  
extinguishers except carbon  
dioxide.  
material eg wood, paper, rubber,  
clothing,  
Flammable liquids, such as  
petrol, diesel, alcohol(spirit),  
kerosene, oil-based paints  
(i) If fire is small use fire blanket or  
Sand.  
(ii) If fire is large use dry powder,  
foam or carbon dioxide  
extinguishers.  
NB: Water should not be used  
as it will make the oil to  
float and keep on burning.  
(i) Dry powder extinguisher.  
(ii) Carbon dioxide extinguisher.  
Flammable gases such as  
butane, propane, biogas,  
methane.  
C
Combustible metals such as  
magnesium, sodium, potassium,  
lithium especially in powder form.  
Cooking oils and fats  
(i) Dry powder extinguisher  
(ii) Foam extinguisher.  
D
F
Wet chemical extinguishers.  
Note:  
Fires caused by electricity are not given their own class because they can fall to any  
other classes. After all, it is not electricity that burns but the surrounding material  
which has been set alight by electric current. Electricity can be source of any of the  
fires class A, B, C, D or F. Therefore, the fires caused by electrical fault are  
extinguished based on the burning materials. Thus, dry powder, dry sand and carbon  
dioxide gas can be used to extinguish this fire.  
Before extinguishing the fire caused by electrical faults, the MAIN ELECTRIC  
SWITCH should be turned off.  
Summary on the classes of fires  
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•
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Class A: Is fire caused by burning solids such as paper, wood, clothing, rubber.  
Class B: Flammable liquids such as paraffin, petrol, oil, spirit, alcohol, etc.  
Class C: Is fire caused by burning flammable gases such as propane, butane,  
methane, hydrogen.  
•
•
Class D: Is fire caused by burning metals such as aluminium, magnesium,  
titanium, sodium, potassium.  
Class F: Is fire in which burning material is Cooking oil or fat in cooking pans.  
FIRE BLANKET EXTINGUISHER  
This type of extinguisher is used to help individuals by stopping fire burning on their  
clothes. The blanket is made of highly heat resistant fibrous silicate mineral called  
asbestos. It is rolled around the individual hence stopping the supply of oxygen.  
SAND BUCKET FIRE EXTINGUISHER  
It is the bucket which contains dry sand. In the accident of small fire, sand is poured  
from the bucket to cover the burning material, hence stops the supply of oxygen.  
PORTABLE FIRE EXTINGUISHERS  
A portable fire extinguisher is an equipment used to put out fires and can be  
easily moved from one place to another.  
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•
•
It is usually hung in an upright position in automobiles and on walls of building such  
as schools and public buildings.  
A portable fire extinguisher consists of a metal container that contains the  
extinguishing agent (substance) stored at high pressure.  
Portable fire extinguishers have ratings or codes on them. This means the  
extinguisher has good firefighting capacity for specific classes of fires.  
The following are different types of portable fire extinguishers are:  
(i) Air pressurized water extinguishers (APW)  
(iii) Carbon dioxide extinguisher  
(v) Foam extinguisher  
(ii) Dry chemical extinguisher (DC)  
(iv) Halon extinguisher  
(vi) Wet chemical extinguishers  
(viii) Blanket extinguisher  
(vii) ABC extinguisher  
(ix) Sand bucket extinguisher  
Reasons for carbon dioxide to be used as fire extinguisher are:  
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Carbon dioxide does not support combustion. It displace oxygen so that oxygen  
cannot come into contact with fire.  
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•
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Carbon dioxide is denser than air. It sinks in fire and smothers a fire.  
Carbon dioxide is very cold, so it cools the fuel.  
Carbon dioxide is not flammable, so it does not catch fire.  
The table below shows chemical composition of the extinguishing agents of  
different portable fire extinguishers  
Type  
Chemical  
composition  
of agent  
Suitable for  
Colour  
code  
Unsuitable for  
APW (Air  
pressurized  
water)  
Red  
Ordinary tap  
water  
pressurized by  
air  
Class A fires (wood,  
paper, rubber, cloth.  
Fires Class B, C and  
D
(will spread the  
flame)  
Dry  
chemical  
(DC)  
Blue  
Fine sodium  
bicarbonate  
powder  
Pressurized by  
nitrogen  
Classes A, B and C  
fires  
Air craft and  
electronics fires,  
Class D fires  
(corrosive to metals  
such as aluminium) ,  
NB: Although it is  
safe to use indoors it  
can obscure vision.  
Black  
Carbon  
dioxide  
Carbon  
dioxide gas  
under  
extreme  
pressure  
Class B, C and fires  
caused by electrical  
faults  
Class A fires  
(Material can re-  
ignite)  
Halon  
Foam  
Green  
Bromochloro-  
difluo-  
methane  
Proteins and  
fluoro-protein  
Potassium  
acetate  
Class A and fires  
caused by electrical  
faults  
Class A and B fires  
Class F  
Class B and C fires  
(least suitable)  
Cream  
Yellow  
Fires caused by  
electrical faults  
Fires caused by  
electrical faults  
Wet  
chemical  
Mono –  
Class A, B and C  
fires  
Fires on Electronic  
equipment  
ammonium  
phosphate  
with a  
ABC  
Blue  
nitrogen  
carrier  
Blanket  
extinguisher Red  
Made by heat Small fires Class A,  
resistant  
fibrous  
B and F, also used  
to rescue an  
Big fires  
Big fires  
mineral called individual by  
stopping fires on  
burning clothes  
asbestors  
Sand  
extinguisher  
sand collected Small fires class A  
in bucket and B  
Red  
NB: (i) For small class A fire (of combustible solids), water can be used to easily put  
out the flames. Small fires that involves flammable liquids should be put out  
using sand or fire blanket. These cut off the oxygen supply.  
(ii) Water should never be used to put out class B (flammable liquids) fires since  
it would spread the flame because it is denser than flammable liquids and the  
flammable liquids float above it.  
(iii)Halon extinguisher is dangerous to use because it is harmful to people’s  
health. But it is used by military forces or aircraft in only few exceptions.  
HOW TO USE A PORTABLE FIRE EXTINGUISHER  
Fire extinguishers should be used in the right way and on the right type of fire. All fire  
extinguishers operate in a similar manner. The acronym ‘PASS’ can be used for quick  
reference. The acronym stands for Pull, Aim, Squeeze and Sweep. The correct  
procedure is summarized below:  
1. Pull (remove) the pin at the top of the extinguisher to make the extinguisher ready  
for use.  
2. Aim at the base and not at the middle or top of the fire otherwise the fire only  
Spread  
3. Squeeze the top lever slowly to release the extinguishing agent in the extinguisher.  
4. Sweep from side to side until the fire is extinguished.  
PRECAUTIONS WHEN USING PORTABLE FIRE EXTINGUISHERS  
1. Keep a reasonable distance (at least 1.5 metres) from the fire as it may suddenly  
change direction.  
2. For a person on fire, use fire blanket instead of a portable extinguisher.  
3. Do not test a portable fire extinguisher at your school without permission.  
4. Do not return a used portable extinguisher to its place.  
5. Do not hold the discharge horn (nozzle) when using carbon dioxide type fire  
extinguisher as it becomes extremely cold that can lead to severe frost burns.  
6. When a fire gets out of control, notify the nearest firefighting squad (fire brigade).  
Causes of laboratory fires  
(i) Gas leakage in the laboratory  
(iv) Gas leakage in the laboratory  
(vii) Explosion of chemicals  
(ii) Smoking material  
(v) Carelessness  
(viii) Electrical faults  
(iii) Negligence  
(vi) Ignorance  
(ix) Inappropriate use of fuels and chemicals  
Ways or measures of preventing fire in the laboratory  
(a)  
(b)  
(c)  
(d)  
(e)  
Put out (extinguish) all glowing residues before you dispose them.  
Use the fuel which meant for a particular burner.  
Cool a burner completely before refilling it with a liquid fuel.  
All flammable chemicals should be locked out of the working laboratory.  
After taking a flammable liquid from its container for an experiment, remove  
the container from the laboratory before you start the experiment.  
Containers of flammable liquids should always be well stoppered.  
Never heat flammable liquids directly with a flame.  
(f)  
(g)  
(h)  
Never pour flammable liquids into the sink.  
Note: (a) The fire caused by burning metals should not be extinguished by water  
because the burning metal can react with water to give hydrogen which is  
another potential fuel hence fire will continue.  
(b) Water is not used to put off fires caused by electrical faults because water  
conduct electricity and give an electric shock that further spreads the fire.  
EXERCISE  
1. A track carrying kerosene was involved in an accident and unfortunately fire broke  
out. With explanation, suggest the fire extinguishers not suitable to use.  
2. A form one student reads a statement from a certain book, “If the clothes worn  
by your friend catch fire, cover them with a fire blanket”. Why a fire blanket is to  
be used in that case?  
3. With a support of vivid examples, explain how you will educate the community to  
avoid the causes of fire accidents.  
C. FLAMES  
Flame is a zone or region of burning gases that produces heat and light.  
It is the visible glowing part of a fire. The flame is formed as a result of burning fuel.  
Factors that determine the colour and temperatures (hotness) of the flame  
•
Type of the fuel used  
• Source of the flame  
• Amount of oxygen supplied  
Types of flames  
There are two types of flames: (i) Luminous flame  
(ii) Non-luminous flame  
LUMINOUS FLAME  
The term “luminous” means giving “giving off light” or “bright” or “shining”.  
Definition: Luminous flame is a flame which is bright yellow in colour and  
produced when the supply of oxygen is not enough to completely burn up of the fuel.  
•
In Bunsen burner, luminous flame is formed when air holes are closed.  
Luminous flame is produced by burning  
candle, spirit lamps, fire wood, piece of  
paper, tin lamp (kibatari) and hurricane  
•
The luminous flame is called a safety flame because it is easily seen, therefore, is  
less likely to cause accidents.  
Question  
Why luminous flame produces a black substance called soot and less heat?  
Answer: It produces soot and less heat because oxygen supplied is not enough to  
complete the burning up of the fuel.  
NON-LUMINOUS FLAME  
The term “non-luminous” means “not giving off light”.  
Non-luminous flame is a flame which is blue in colour because there is a sufficient  
supply of oxygen and so the fuel burns completely.  
•
In Bunsen burner, non-luminous flame is formed when air holes are opened.  
Non-luminous flame can be produced by gas  
stove, candle and Bunsen burner.  
•
Non- luminous flame can easily cause accidents in the laboratory because cannot be  
seen easily therefore, one may not be aware that the burner is on.  
NB: Gas stove, kerosene stove and Bunsen burner can be regulated to form both  
luminous and non-luminous flames.  
THE BUNSEN BURNER  
A Bunsen burner is a laboratory heat source which consists of a vertical metal tube  
connected to a gas source.  
The Bunsen burner is named after the German chemist Robert Bunsen who invented  
it in 1855. The Bunsen burner is able to produce a very hot flame of temperature up  
to 1000 oC from a mixture of gas and air.  
PARTS OF THE BUNSEN BURNER  
These include base, gas inlet, jet, collar (metal ring), air hole, barrel (chimney).  
FUNCTIONS OF DIFFERENT PARTS OF THE BUNSEN BURNER  
Base: It supports the Bunsen burner. It makes the burner stable.  
Gas inlet: Allows the gas to enter in the Bunsen burner from the gas supply.  
Jet: Directs the gas to the barrel (chimney).  
Collar: Controls (Regulates) the amount of air entering the burner.  
Air holes: Allow air to enter in the burner.  
Barrel: It is where mixture of air and gas burns.  
HOW THE BUNSEN BURNER WORKS  
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Gas enters the burner through gas inlet.  
Air enters the burner through the air holes.  
The amount of air entering the burner is controlled by turning the collar.  
At the top of the barrel, the mixture of air and gas burns to produce a flame.  
When air holes are closed the amount of oxygen is less and luminous flame is  
produced.  
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When air holes are partially opened, there is more oxygen and flame produced is  
medium.  
When the air holes are fully opened, there is enough oxygen and Non-luminous  
flame is produced.  
HOW TO LIGHT A BUNSEN BURNER  
The following are correct steps (procedures) on how to light the Bunsen burner:  
1. Close the air holes of the burner.  
2. Connect the Bunsen burner to the gas tubing (gas supply).  
3. Light a match or wooden splint and hold it on top of the barrel  
4. Slowly turn on the gas until the gas light up  
5. Open the air holes halfway and then fully (Turn the collar to adjust the air holes)  
6. Adjust the gas tap until the gas supply is enough to produce a non-luminous  
flame.  
BURNING BACK (STRICKING BACK) OF THE BUNSEN BURNER  
Burning back occurs when too much air enters the burner so that the flame burns  
back into the burner tube or at the jet.  
The following can be the causes of burning back of the Bunsen burner  
(i) Insufficient gas pressure  
(ii) Excessive air flow  
(iv) Damaged burner  
(iii) Blockage of the jet or gas inlet  
WHAT TO DO AFTER BURNING BACK?  
1. Turn off the gas tap  
2. Close the air holes  
3. Turn on the gas tap  
4. Re- lights the Bunsen burner.  
HOW TO PREVENT BURNING BACK  
1. Ensure gas supply is sufficient  
2. keep the burner nozzle (jet) and air inlet clean  
3. Avoid over heating or prolonged use of the burner.  
A. PARTS OF LUMINOUS FLAME  
Luminous – flame has four parts (zone) which are  
(i) Thin outer zone  
(ii) Yellow middle zone  
(iii) Inner unburnt zone  
(iv) Blue outer zone  
1. Thin Outer zone - This is a region of complete combustion of gas which gives out  
light. It is almost a colourless zone  
2. Yellow middle zone – This is a region of incomplete combustion of gas and gives  
out soot.  
3. Inner unburnt zone - This is dark, cool and contains unburnt gas  
4. Blue outer zone – Due to rising convectional current, there is sufficient supply of  
air for complete burning at this zone.  
B. PARTS OF NON-LUMINOUS FLAME  
Non – luminous flame has three parts (zones) which are  
(i) Colourless inner zone  
(ii) Blue – green middle zone  
(iii) Pale purple – blue outer zone  
1. Pale purple - blue outer zone: It is a zone (region) where complete burning of  
the gas occurs.  
2. Blue-Green middle zone - Part of the gas burns in this zone because there is  
no enough air to burn all the gas completely. The hottest part of the flame is at  
the tip of this blue- green zone.  
3. Colourless (Cool) inner zone – It is a zone (region) of unburnt gas.  
CHARACTERISTICS OF FLAMES  
LUMINOUS FLAME  
1. It has four (4) zones  
2.It forms soot  
NON-LUMINOUS FLAME  
It has three (3) zones  
Does not form soot  
3. It is yellow in colour  
4. It is not very hot  
It is blue in colour  
It is very hot  
5. It is not noisy (Burns quietly)  
6. It does not burn back  
7. It is tall and shapeless  
(Has a wavy flame) Has a  
It is noisy (Burns with roaring noise)  
Sometimes it burns back  
It is short and cone like  
(Has a triangular flame)  
triangular flame  
USES OF LUMINOUS FLAME: It is mainly used for lighting because  
(i) It is bright yellow in colour (ii) It is also not very hot;  
Therefore, it is safer for lighting than the non – luminous flame. It is not suitable for  
heating /cooling because it is not very hot and produces soot. Example candle flame,  
tin lamp flame, hurricane lamp flame.  
USES OF NON-LUMINOUS FLAME  
(a) It is used for heating because it gives a lot of heat.  
(Bunsen burner and liquefied petroleum gas burners can be used for heating)  
(b) It is used for cooking because it gives enough heat and it does not produce soot  
(c) It is used for welding because it is very hot.  
Welding is the joining together of metal pieces or parts  
(d) It is used in the flame test of some chemical substances.  
A flame test is the introduction of a sample of the desired substance to non-  
luminous flame and observing the colour change). Example sodium produce  
golden yellow flame and calcium produces brick-red flame.  
NB: • Natural sources of heat is the sun.  
•
Artificial heat sources are man-made sources such as heat from the spirit  
burner, Kerosene stove, Bunsen burner and gas stove.  
Heat sources used in the laboratory includes: (i) spirit burner  
(iii) Kerosene stove (iv) Bunsen burner (v) Electric burner  
(ii) Gas stove  
REVISION EXERCISE THREE  
1. (a) Why a luminous flame is preferred for lighting over a non-luminous flame?  
Give two reasons  
(b) Give four reasons why Bunsen burner is the best heat source compared to  
other burners in chemistry laboratory.  
(c) What are the similarities between luminous flame and non-luminous flame?  
(d) Why sprit lamp flame is not mostly used in the laboratory as source of heat?  
2. (a) The Bunsen burner produces both luminous flame and non-luminous flame.  
(i) Which between these flames is hotter than the other? Why?  
(ii) Which flame can be easily seen? Why?  
(iii) Which flame is preferred to be used in the laboratory? Why?  
(b) Why the outer zone of the flame is hotter than other parts of the flame?  
(c) Which part of the flame is coolest of all? Why?  
(d) Name three activities that need non-luminous flame to be used  
3. Students went to camp in an isolated area where they needed to make tea using  
a portable stove. Which type of flame would be selected, and what are the  
practical reasons behind their choice?  
4. What determine the choice of an appropriate firefighting equipment in the event  
of fire accidents?  
5. What are some common problems that could arise when using a Bunsen burner,  
and what solutions would you recommend?  
6. Why is not advised to use water for extinguishing Class B fire and the fire caused  
by electrical faults? Explain  
7. A student was preparing food for the family by a deep-frying method.  
Accidentally, the cooking pan tipped over and a huge fire spread on the kitchen  
floor.  
(a) Identify the fuel in this fire accident.  
(b) Which fire extinguishers would be suitable for putting out the fire? Explain  
(c) Which fire extinguishers would not be suitable for putting out the fire? Explain  
8. If a gas cooker is involved in a fire accident, what steps can be taken to  
extinguish the fire safely? Explain  
9. How a non-luminous flame is used in flame test of certain chemical substance?  
Explain.  
10. Give any three (3) differences between burning and combustion.  
11. Although water contains oxygen which supports combustion, but it is used to  
extinguish class A fires. Give two (2) reasons.  
12. The figure below is a diagram of the apparatus which is commonly used in the  
laboratory. Study it carefully and use it to answer the questions that follow.  
(a) Give the name of the apparatus and state its major uses.  
(b) Label the parts marked A, B, C, D, E and F and state the uses of each part.  
(c) How part ‘B’ should be adjusted so as to produce a clean flame? Explain  
(d) Why the apparatus is much preferred in the laboratory other than other  
apparatus like kerosene lamp and spirit lamp? Give three (3) reasons.