Fire is a chemical reaction that requires three elements to be present for the chemical reaction to take place and continue. The three elements are:-
- Heat or an igniation source
- Fuel
- Oxygen
These three elements are typically refered to as the “fire triangle” .
Igniation sources can include any material, equipment, operation that emits a spark or flame including obvious items, such as torches,as well as less obvious items, such as static electricity and grinding operations. Equipment or components that radiate heat, such as kettles,catalytic converters and mufflers,also can be ignition sources.
Fuel sources include combustible materials
Such as wood,paper,trash, clothing, flammable liquids, flammable gases.
OSHA describes a hazardous atmosphere as one which is oxygen-deficient because it has less than 19.5 percent or oxygen enriched greater than 23.5 percent.
Fire Classification:-
Class A :- fires involving ordinary combustibles, such as paper,trash,some plastics,wood, clothes. A rule of thumb is if it leaves an “ash” behind, it is a class A fire.
Class B:- fires involving flammable gases or liquids,such as propane,oil,gasoline.
Class C:- fires involving energized electrical components.
Class D:- fires involving metal. A rule of thumb is if the name of metal ends with the letters ends with “um” it is Class D fires.
Class K:- fires involving vegetable or animal cooking oils or fats.
Types of fire extinguishers:-
Dry chemical (multi purpose):- it can be used for A,B,C, types of fires, Generally good for use in roofing industry.
Foam-alcohol-resistant and aqueous film-forming foam (AFFF) types:- it can be used for Class B fires. Expensive;effective on Class B only; limited shelf life,generally not need in roofing industry.
Water:- Used for Class A fires.
Metal X:- Used for Class D,B,C fires. Expensive;must kept dry.
Carbon Dioxide:- Used Class B,C fires.
Note:- if Carbon Dioxide fire extinguisher used in confined space will create oxygen deficiency,not effective in windy condition,can cause frostbite during discharge.
Potassium Acetate :- Used for Class K fires, Expensive,Wet chemical extinguisher .
Halon:- Used for Class B,C fires,Expensive,
Note:- Toxic gases may be released in extremely hot fires because of decomposition,not effective in windy conditions.
Note:- Dry chemical fire extinguisher can extinguish three fire Classes A,B,C.
Note :- Minimum rated 10B fire extinguisher provided with in 50 feet of the point of job site where more than 50 gallons of flammable or combustible liquids or 5 pounds of flammable gas.
PASS method :-
- P :- Pull the pin on the extinguisher
- A:- AIM at base of the fire
- S:- SQUEEZE handle
- S:- SWEEP at the fire,moving from side to side.
Note:- Post no smoking signs around flammable liquids and gases, fire watches on all work involving torch applied materials of a minimum of two hours after the last torch is turned off.
Fire extinguish methods:-
Cooling:- Removal of heat from the scene of fire is called as cooling.
Starvation:- Removal of fuel from the scene of fire is called as starvation. By cutting fuel supply.
Smoothering :- Removal of oxygen from the scene of fire is called as smoothering. By using carbon monoxide,DCP fire extinguisher.
Chain reaction:- Brake the chain by DCP,Blanketing, applying agents to interfere with chemical chain reaction, breaking down the products of combustion through heat and oxidation.
Note:- Fire= Fuel + oxygen+Heat+Chain reaction . It is also called as ” tetrahedron”
HSE Guruji 