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Basic Fire Chemistry
In order for a fire to start, there are three elements that must be present at the same time, in proper quantity. These elements are:
- fuel
- oxygen
- heat
When two of the conditions exist, the other may not be far behind.
Components of a Fire
Fuel
Fuel is present in the form of flammable vapors, paper, rags, and clothing.
Oxygen
The atmosphere contains approximately 21 percent oxygen. Fire needs only 16 percent oxygen to ignite and spread. So, there is always enough oxygen present in the air for a fire.
Heat
Fortunately, the final component, heat is not always present; it must be supplied. The first precaution against fire is to prevent the presence of any flame, spark or heated surface that could cause ignition.
It takes all three elements (fuel, heat, and oxygen) to produce a fire.
Therefore, the easiest way to defeat a fire is to eliminate one or more of the sides of the fire triangle.
- Remove the fuel.
- Exclude the Oxygen.
- Eliminate the heat.
Types of Fires
The National Fire Protection Association has divided fires into 5 types determined by the materials or fuel being burned. The fire extinguishers have labels on them specifying which types of fire they control.
- Class A: Ordinary Combustibles
- Class B: Flammable Liquids
- Class C: Electrical Equipment
- Class D: Combustible Metal
- Class K: Cooking Oils & Fats
Most common household fires are A, B or C class fires. A common household fire extinguisher will put out an A, B or C class fire.
| Class A: Ordinary Combustibles – ASH
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Class B: Flammable Liquids – BOILS
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Class C: Electrical Equipment – CURRENT
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| Class A fires are fueled by ordinary combustibles such as paper, wood, cloth, rubber, plastic products, and rubbish.
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Class B fires are fueled by flammable liquids such as alcohol, kerosene, oil, paint, certain cleaning supplies, and gasoline. A majority of these liquids emit flammable vapors that can ignite fires.
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Class C fires involved energized electrical equipment such as a fuse/breaker box, conditioned air unit, space heater, or computer terminal.
Note: The power must be turned off and the equipment unplugged before extinguishing an electrical fire. |
Electrical Fires
Electrical fires happen all the time, especially in older homes. Cords that are plugged in for lengthy periods of time can overheat and catch something nearby on fire. Common household triggers are irons, curling irons, flat irons, self-cleaning ovens and candles left burning.
Fire Extinguishers
When you do your initial walkthrough in a client’s home, note the doors leading to outside and ground floor windows as possible fire escapes. Ask if they own a fire extinguisher and where they keep it. Many people will keep one in the pantry and they’ll usually keep a second or third one upstairs in a common room of the house. Knowing where these are could save your life in the event of a fire. Most modern homes are equipped with smoke alarms that will alert you a fire is coming.
Fire extinguishers should be inspected monthly and maintenance is required annually by a qualified vendor. In people’s homes, they rarely do these inspections. So ask the client if their fire extinguishers have been maintained properly.
Most people buy them and forget about them. So if the fire extinguisher is new and hasn’t ever been used, it is probably in working conditions.
There are different types of fire extinguishers for the various types of fires. Fire extinguishers are labeled to show what types of fires they are made to extinguish. You’ll learn all about the various types and what types of fires they put out in your OSHA training.
For homes, the most common fire extinguisher is the dry chemical. It can be used on Class A, Class B and Class C fires. Check the label to make sure it will put out the type of fire you have.
First Steps
The first step in any fire situation is to notify the fire department. This applies to all fires no matter how small. Even if it has been extinguished.
Fighting a Fire
All of the conditions must exist before attempting to fight a fire.
- Know where the fire extinguishers are and how to use them.
- The fire is confined and not spreading.
- Hazardous materials such as fuels, cleaning chemicals or toxic fumes are not involved.
- The fire can be fought with your back towards an exit (door or window) unless the fire is between you and the only available exit and fighting the fire is necessary to evacuate.
Note: If you have a (Class C) fire caused by electrical equipment, unplug the current or flip the breaker. If you can do it safely.
Should you have to use a fire extinguisher, check to see if it is labeled for an A, B, or C class fires then PASS.
PASS
P – Pull the pin
A – Aim at the base of the fire
S – Squeeze the trigger
S – Sweep back and forth until you’ve put out the fire.
If a fire occurs in the home while you are cleaning and you can contain it – do.
Call For Help 
If you cannot contain a fire, help anyone or pets in the house outside, stay outside with them, and call 911 for help.
Often the fire department will dispatch a fire truck and firemen but keep you on the phone to get all the necessary information from you.
Make sure you have the address of your location. (Put the 911 call on speaker, check your contacts info on your smartphone, and pull up the client’s name, address and phone to give to the fire dept. Your notes should also include if there is an animal at home and its name.)
Specify how bad the damage is, has the fire been put out, is it still burning? Did you unplug the electrical equipment that caused the fire? Are you out of the house? Is everyone safe?
Survival Basics
- Fire moves quickly and follows the path of least resistance.
- Crawl on the floor below the level of smoke.
- Close doors behind you as you move away from the fire to keep smoke and flames out.
- Do NOT open hot doors. Feel the temperature of the door with the back of your bare hand. If it’s hot. DO NOT OPEN IT.
- When in doubt – get out.
