Firefighting

Fire is the state or process of combustion in which ignited material combines with oxygen and gives off light, heat and flame.

COMPONENTS NEEDED TO START A FIRE

A fire will start or continue to burn if three factors are satisfied. The three components can be summarized by the fire triangle
  1. Fuel
  2. Heat
  3. Oxygen

Classification of fire

Fire classed into:
Class Burning materials Appropriate fire extinguisher
A Ordinary solid combustible materials eg. paper and wood
  • Use water
  • Any type of portable fire extinguisher except carbon dioxide.
B Flammable liquids such as petrol, kerosene and diesel.
  • If fire is small, use a fire blanket or sand.
  • If the fire is large, use dry powder, form or carbon dioxide extinguishers.
C Flammable gases such as butane and propane.
  • Dry powder extinguisher.
  • Carbon dioxide extinguisher.
D Combustible metals such as magnesium, sodium and potassium.
  • Dry powder extinguisher.
  • Foam extinguisher.
F Cooking oils and fats Wet chemical extinguisher.

Ways of preventing harmful fires in the laboratory or any place:

  1. Cool a burner completely before refilling it with a liquid fuel.
  2. Never heat flammable liquids directly with a flame.
  3. All flammable chemicals should be locked of the laboratory.
  4. Extinguish all glowing residues before you dispose of them.
  5. Never pour flammable liquids into the sink.

PORTABLE FIRE EXTINGUISHER

This is the one that can be easily moved from one place to another.
It consists of a metal container that contain the extinguishing agent (substance) stored at high pressure.

Composition of some portable fire extinguishers

Type of fire extinguisher Chemical composition
Air pressurized water Ordinary tap water pressurized by air.
Dry chemical Fine sodium bicarbonate powder pressurized by nitrogen.
Carbon dioxide Carbon dioxide gas under high pressure.
Halon Bromochloro-difluoro-methane.
Foam Proteins and fluoro-proteins
Wet chemical Potassium acetate
ABC Monoammonium phosphate with a nitrogen carrier.

Steps for extinguishing fires by using portable fire extinguishers.

The main steps can be easily remembered by using PASS mnemonic.
  1. P- Pull the pin to make the extinguisher ready for use.
  2. A- Aim at the base of the fire not at the top, otherwise the fire only spreads.
  3. S- Squeeze the top lever to release extinguishing agent.
  4. S-Sweep from side to side until the fire is extinguished.

Precautions to be taken when using portable fire extinguishers:

  1. Keep a reasonable distance from the fire as it may suddenly change direction.
  2. Do not test a portable fire extinguisher without permission.
  3. Do not return a used portable fire extinguisher to the wall.
  4. For a person on fire, use a fire blanket instead of portable fire extinguisher.
  5. When a fire gets out of control, abandon it and notify the nearest firefighting squad (fire brigade).

NOTE

Water should not be used to extinguish fire involving class B and E.

Class Discussion

Give reasons
  1. Carbon dioxide is used as a fire extinguisher.
    Because carbon dioxide is denser than air therefore it displaces air from burning substance and cover the burning substance depriving it oxygen (or preventing oxygen from reaching the burning substance).
  2. Water cannot be used to extinguish fire involving class B.
    Water is denser than most of flammable liquids. Therefore it sinks at the bottom leaving flammable liquids at the top continue burning.
    Because it spreads flames.
  3. Water is not used to extinguish class E fire.
    Water is a good conductor of electricity, therefore it increases conductivity.