Title F I , NOTES, 2025, FIRE, FIRE FIGHTING AND FLAMES TOPIC 4.pdf ✅

1 FIRE, FIRE FIGHTING AND FLAMES 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. (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 Most firefighting equipment work by cutting off the oxygen supply to the fire to effectively extinguish it. NB: (i) Fuel: is a substance that releases energy when burning eg 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. (iii) Heat: 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. FIRE FIGHTING Uncontrolled fires can be dangerous and destructive leading to injuries, property damage and environmental harm. Firefighting is the act of extinguishing of harmful fires and mitigating (reducing) their effects. Materials which are used to put out fires are called Fire extinguishers. Fire fighting involves eliminating at least one of the three components in the fire triangle. Most firefighting equipment work by cutting off the oxygen supply to the fire to extinguish it effectively. CLASSIFICATION OF FIRE 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 A Ordinary SOLID combustible material eg wood, paper, rubber, clothing, (i) use water (ii) Any type of portable extinguishers except carbon dioxide. B 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 C Flammable gases such as butane, propane, biogas, methane etc (i) Use Dry powder extinguisher (ii) Use Carbon dioxide extinguisher D Combustible /burning metals, such as magnesium, sodium, potassium, lithium especially in powder form. (i) Dry powder extinguisher (ii) Foam extinguisher
2 F Cooking oils and fats Use wet chemical extinguishers NB: Fires caused by electricity are not given their own class because they can fall to any other classes. This is because it is not electricity that burns but the surrounding material which has been set a light 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 but before starting to extinguish the fire MAIN SWITCH should be put (turned) off. SUMMARY ON THE CLASSES OF FIRES Class A: Is fire caused by burning solids such as paper, wood, clothing, rubber, etc 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, etc 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 etc PORTABLE FIRE EXTINGUISHERS Portable fire extinguisher is an equipment used to put out fires and can be easily moved from one place to another. 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) (ii) Dry chemical extinguisher (DC) (iii) Carbon dioxide extinguisher (iv) Halon extinguisher (v) Foam extinguisher (vi) Wet chemical extinguishers (vii) ABC extinguisher (viii) Blanket extinguisher (ix) Sand bucket extinguisher THE TABLE BELOW SHOWS CHEMICAL COMPOSITION OF THE EXTINGUISHING AGENTS OF DIFFERENT PORTABLE FIRE EXTINGUISHERS. Type Colour code Chemical composition of agent Suitable for Unsuitable for APW (Air pressurized water Red Ordinary tap water pressurized by air Class A fires (wood, paper, rubber, cloth etc 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. Carbon dioxide Black Carbon dioxide gas under extreme pressure Class B, C and fires caused by electrical faults Class A fires (Material can re-ignite) Halon Green Bromochloro-difluo- methane Class A and fires caused by electrical faults Class B and C fires (least suitable) Foam Cream Proteins and fluoro- protein Class A and B fires Fires caused by electrical faults Wet chemical Yellow Potassium acetate Class F Fires caused by electrical faults ABC Blue Mono –ammonium phosphate with a Class A, B and C fires Fires on Electronic equipment
3 nitrogen carrier Blanket extinguisher Red Made by heat resistant fibrous mineral called asbestors Small fires Class A, B and F, also used to rescue an individual by stopping fires on burning clothes Big fires Sand extinguisher Red Composed of sand collected in bucket Small fires class A and B Big fires 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. 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 ON USING FIRE EXTINGUISHERS The following are some safety precautions you have to keep in mind when using fire extinguishers: 1. Keep a reasonable distance (at least 1.5M) from the fire as it may suddenly change direction. 2. Never use a portable extinguisher for person (people) on fire, instead use a fire blanket. 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. 5. When a fire gets out of control, notify the nearest fire brigade. 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.