About Fire and Extinguishers
A fire extinguisher is an absolute need for any home or office. While there’s a decent possibility that the extinguisher will sit on the divider for quite a long time, gathering dust, it could wind up sparing your property and even your life.
We’ll see exactly see what a fire extinguishers does. Let’s find out what causes fire, and know the correct way to use an extinguisher and see which fire suppressant works best on different types of fires.
Fire is the result of a chemical combustion reaction, typically a reaction between oxygen in the atmosphere and some sort of fuel (wood or oil, for example). Of course, wood and gasoline don’t spontaneously catch on fire just because they’re surrounded by oxygen. For the combustion reaction to take place, the fuel has to be heated to its ignition temperature.
As you can see, there are three essential elements involved in this process:
- Fuel (something to burn—such as wood or coal).
- Oxygen (usually from the air).
- Heat.
There are three main types of extinguisher and they work in slightly different ways:
- Water extinguishers, which are the most common, are essentially tanks full of water with compressed (tightly squeezed) air as the propellant to make them come out. Water extinguishers work by removing heat from the fire.
- Dry chemical extinguishers are tanks of foam or dry powder with compressed nitrogen as the propellant. They work by smothering the fire: when you put a layer of powder or foam on the fire, you cut the fuel off from the oxygen around it, and the fire goes out.
- Carbon dioxide (CO2) extinguishers contain a mixture of liquid and gaseous carbon dioxide (a nonflammable gas). CO2 is normally a gas at room temperature and pressure. It has to be stored under high pressure to make it a liquid. When you release the pressure, the gas expands enormously and cools to make a huge white jet. CO2 attacks the fire triangle in two ways: it smothers the oxygen and, because it’s so cold, it also removes heat.
That classifies extinguishers by what they contain. You’ll also find fire extinguishers classified by the types of fires you can use them on. This gives us five different kinds:
- A: Green: For wood, cloth, and paper.
- B: Red: For combustible and flammable liquids such as oil, gasoline, and paint.
- C: Blue: For electrical equipment and tools.
- D: Orange: For flammable metals.
- K: Black: For animal or vegetable oils or cooking facts.
It’s important always to use the right extinguisher for the fire. Using the wrong extinguisher can put your life in danger and make the fire worse. For example, you must never use water extinguishers on electrical fires because you could electrocute yourself and the people nearby. If you’re in the slightest doubt about tackling a fire, leave it alone and get yourself to safety.
Fire extinguishers are sturdy metal cylinders filled with water or a smothering material. When you depress a lever at the top of the cylinder, the material is expelled by high pressure, similar to the way material is forced out of an aerosol can. The diagram below shows a typical design.
In this extinguisher, a plastic siphon tube leads from the bottom of the fire-suppressant reservoir to the top of the extinguisher. A spring-mounted valve blocks the passageway from the siphon to the nozzle. At the top of the cylinder, there is a smaller cylinder filled with a compressed gas — liquid carbon dioxide, for example. A release valve keeps the compressed gas from escaping.
To use the extinguisher, you pull out the safety pin and depress the operating lever. The lever pushes on an actuating rod, which presses the spring-mounted valve down to open up the passage to the nozzle. The bottom of the actuating rod has a sharp point, which pierces the gas cylinder release valve.
The compressed gas escapes, applying downward pressure on the fire-suppressant material. This drives the material up the siphon and out the nozzle with considerable force. The proper way to use the extinguisher is to aim it directly at the fuel, rather than the flames themselves, and move the stream with a sweeping motion.
One popular extinguisher material is pure carbon dioxide. In a carbon dioxide extinguisher, the carbon dioxide is kept in pressurized liquid form in the cylinder. When the container is opened, the carbon dioxide expands to form a gas in the atmosphere. Carbon dioxide gas is heavier than oxygen, so it displaces the oxygen surrounding the burning fuel. This sort of fire extinguisher is common in restaurants because it won’t contaminate the cooking equipment or food.
The most popular extinguisher material is dry chemical foam or powder, typically made of sodium bicarbonate (normal baking soda), potassium bicarbonate (nearly identical to baking soda), or mono ammonium phosphate. Baking soda starts to decompose at only 158 degrees Fahrenheit (70 degrees Celsius), and when it decomposes, it releases carbon dioxide. The carbon dioxide, along with the insulation of the foam, works to smother the fire.
Most fire extinguishers contain a fairly small amount of fire-suppressant material — you can use it all up in a matter of seconds. For this reason, extinguishers are only effective on relatively small, contained fires. To put out a larger fire, you need much bigger equipment — a fire engine, for example — and the professionals who know how to use it. But for the dangerous flames that can pop up in your house, a fire extinguisher is an invaluable lifesaver.
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