To understand how fire extinguishers work, you first need to know a little about fire. Three elements must be present at the same time to cause the chemical exothermic reaction – fire.
1. Oxygen to support combustion,
2. Sufficient heat to raise the temperature of the material to its flash point.
3. Fuel or combustible material
Oxygen, heat and fuel are called the “fire triangle”. If you remove any of these three elements, no fire will occur or the fire will be extinguished.
Essentially, fire extinguishers extinguish a fire by removing one or more elements from the fire triangle.
Fire safety, at its most basic, is based on the principle of separating fuel sources and ignition sources.
Types of fires
Not all fuels are created equal, and if you use the wrong type of fire extinguisher on the wrong type of fuel, you can actually make things worse. This is why it is very important to understand the four different classifications of “fuel”.
Class A – Wood, paper, cloth, trash, plastic. Solid combustible materials other than metals.
Class B – Flammable liquids: gasoline, oil, grease, acetone. Any ignited non-metal in the liquid state.
Class C – Electrical: Live electrical equipment which, while “plugged in” to the mains, will be considered a Class C fire.
Class D – Metals: potassium, sodium, aluminum, magnesium
Unless you work in a laboratory or in an industry that uses these materials, it is unlikely that you will have to deal with a Class D fire. Special extinguishing agents (Metal-X, foam) are required to extinguish such a fire.
Most fire extinguishers have a label with a pictogram that indicates which type of fire the fire extinguisher is intended for.
TYPES OF FIRE EXTINGUISHERS
Water fire extinguisher
Water extinguishers are filled about two-thirds of the bottle with regular tap water, then pressurized with air. Essentially, a water extinguisher is just a giant “water gun”. They are only intended for Class A fires (wood, paper, cloth).
What you need to remember about water fire extinguishers
Never use water to extinguish flammable liquid fires. Water is extremely ineffective at putting out this type of fire, and you can actually spread the fire if you try to use water on it.
Never use water to extinguish an electrical fire. Water is a good conductor and can give you an electric shock. Electrical equipment, including computers, must be unplugged before using a water extinguisher on it.
A water extinguisher extinguishes a fire by removing the “heat” element of the fire triangle.
Carbon dioxide fire extinguishers
Carbon dioxide fire extinguishers are filled with non-flammable carbon dioxide gas under extreme pressure. You can recognize a CO2 fire extinguisher by the hard funnel and the lack of a pressure gauge.
CO2 cylinders are red and range from 2kg to 30kg or more. For the larger sizes, the rigid funnel will be located at the end of a long, flexible hose.
The CO2 fire extinguisher label is designed for Class B and C (flammable liquids and electrical) fires.
Carbon dioxide extinguishes the fire by displacing the oxygen or taking away the oxygen element of the fire triangle. Carbon dioxide is also very cold as it comes out of the extinguisher under pressure and forms dry ice, so it cools the combustible material. CO2 may be ineffective in extinguishing Class A fires because they may not be able to displace enough oxygen to successfully extinguish the fire. Class A materials can also smolder and re-ignite.
CO2 is often found in laboratories, mechanical rooms, kitchens and areas where flammable liquids are stored. All CO2 extinguishers are hydraulically tested and recharged every five years.
Powder fire extinguishers
Powder fire extinguishers are available in different types. You may see them labeled: “DC” short for “dry chem”, “ABC” indicating they are designed to extinguish Class A, B and C fires, or “BC” indicating they are intended for extinguishing class B and C fires.
Powder fire extinguishers are filled with a fine yellowish powder. The largest part of this powder consists of monoammonium phosphate. Nitrogen is used to pressurize fire extinguishers. ABC extinguishers are red and range from 1kg to 50kg or more.
It is extremely important to determine which types of powder fire extinguishers are available in your area. Read the labels and know their location! You don’t want to mistakenly use a “BC” extinguisher on a Class A fire thinking it’s an “ABC” extinguisher. Powder extinguishers extinguish a fire by covering the fuel with a thin layer of powder, separating the material from the oxygen in the air. The powder also works to interrupt the chemical reaction of the fire, so these fire extinguishers are extremely effective at extinguishing a fire.
These fire extinguishers can be used in laboratories, production facilities, break rooms, chemical warehouses, offices, vehicles, etc. Powder extinguishers designed for Class B and C fires can be located in places such as restaurants, kitchens or areas with flammable liquids.
FIRE EXTINGUISHING RULES
Fires can be very dangerous and you should always make sure that you do not endanger yourself or others when trying to put out a fire. For this reason, when a fire occurs:
SET OFF THE ALARM. If you discover or suspect a fire, activate the building’s fire alarm. If there is no alarm in the building, alert other occupants by knocking on doors and shouting as you leave.
LEAVE THE BUILDING. Only attempt to rescue others if you can do so safely. Move away from the building and out of the way of the fire department. Do not re-enter the building until the fire department says it is safe to do so.
CALL THE FIRE DEPARTMENT. Dial 112. Give as much information as possible to the emergency dispatcher. Complete and immediate evacuation is safest. Only use a fire extinguisher if the fire is very small and you know how to do it safely. If you cannot put out the fire, leave immediately. Make sure the fire department is called – even if you think the fire is out.
Before you decide to fight the fire yourself, keep the following rules in mind:
NEVER EXTINGUISH A FIRE IF:
1. You don’t know what’s on fire. If you don’t know what’s burning, you don’t know what type of extinguisher to use. Even if you have an ABC extinguisher, there may be something in the fire that will explode or produce highly toxic smoke. You’ll probably know what’s on fire, or at least have a pretty good idea, but if you don’t, let the fire department handle it.
2. The fire spreads rapidly beyond the place where it started. The time to use a fire extinguisher is in the initial stages of a fire. If the fire is already spreading quickly, it is best to simply evacuate the building, closing the doors and windows behind you as you exit.
3. Your instincts tell you not to. If for any reason you feel uncomfortable with the situation, just let the fire department do their job.
4. The final rule is to always position yourself with an exit or means of escape behind you before attempting to use a fire extinguisher to extinguish a fire. In the event that the fire extinguisher fails or something unexpected happens, you need to be able to get out quickly and you don’t want to be trapped. Just remember, always keep an exit behind you.
HOW TO USE A FIRE EXTINGUISHER:
1. Pull the pin. This will allow you to activate the fire extinguisher.
2. Aim at the base of the fire. If you aim at the flames (which is often the temptation), the extinguishing agent will fly right over and do no good. You have to hit the “fuel”.
3. Squeeze the top handle or lever. This pushes a button that releases the contents of the extinguisher, which is under pressure.
4. Move the hose with the extinguisher funnel around the fire until the fire is completely extinguished. Start using the fire extinguisher from a safe distance, then move on. Once the fire is out, monitor the area in case it starts up again.