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Though it's likely your fire extinguisher will remain on the wall, gathering dust for years, it holds the potential to protect your property—and possibly even your life. Jeffrey Coolidge / Getty ImagesA fire extinguisher is a vital tool in every home or office. Even though it may just collect dust on the wall, it can make all the difference in protecting your home or business when a fire occurs.
In this article, we’ll explore the function of fire extinguishers, how they operate, and the causes of fires. Additionally, we’ll guide you on the proper use of a fire extinguisher and identify which fire suppressant is most effective for various types of fires.
The Science Behind Fires
Fire occurs as a result of a chemical combustion process, generally involving a reaction between oxygen from the air and a fuel source such as wood or gasoline.
However, wood and gasoline don’t ignite just because they are exposed to oxygen. For combustion to happen, the fuel must first be raised to its ignition temperature.
Here’s how a typical wood fire unfolds:
- Something raises the temperature of the wood to very high levels. This could be focused light, friction, or another fire source.
- Once the wood reaches around 500 degrees Fahrenheit (260 degrees Celsius), the heat breaks down some of the cellulose that makes up the wood.
- The decomposed material is released as volatile gases, usually a combination of hydrogen, carbon, and oxygen.
- At high temperatures, the compound molecules break apart, and the atoms recombine with oxygen to form water, carbon dioxide, and other substances.
- The rising gases create the flame. As carbon atoms rise through the flame, they emit light as they heat up. (Check out How Light Bulbs Work to learn why heated objects emit light.)
- The heat from the flame keeps the fuel at its ignition temperature, enabling the fire to continue as long as there’s fuel and oxygen.
As you can see, three key elements are necessary for this process:
- Intense heat
- Oxygen (or a similar gas)
- Fuel
Fire extinguishers work by eliminating at least one of these essential components, causing the fire to extinguish.
The Inner Mechanisms of a Fire Extinguisher
Most dry-chemical fire extinguishers feature a built-in pressure gauge. If the gauge reads "recharge," the pressure may be too low to discharge the contents. The National Fire Protection Association advises having dry extinguishers inspected every six years, even if the gauge shows proper pressure.Three critical elements are needed to ignite a fire: heat, oxygen, and fuel. To extinguish a fire, you must effectively eliminate one of these elements.
- The most effective way to eliminate heat is to pour water on the fire. This reduces the temperature of the fuel below its ignition point, halting the combustion process.
- To remove oxygen, you can suffocate the fire to prevent exposure to air. One method for smothering a small fire is to cover it with a heavy blanket. Alternatively, you can cover it with nonflammable substances like sand or baking soda.
- Removing fuel is typically the hardest method to implement for most fires. For example, in a house fire, the house itself acts as fuel. The fuel is only removed once it has been consumed by the fire.
A portable fire extinguisher is a robust metal canister filled with water or a fire-suppressing substance (the extinguishing agent). When you press or squeeze the lever at the top of the cylinder, the material is expelled under high pressure, much like the contents of an aerosol can.
Within this extinguisher, a plastic siphon tube runs from the bottom of the fire-suppressant reservoir to the top of the device. A spring-loaded valve blocks the pathway between the siphon and the nozzle.
At the top of the cylinder, there is a smaller chamber containing compressed gas—such as liquid carbon dioxide. A release valve ensures that the compressed gas stays contained until needed.
To operate the extinguisher, first remove the safety pin and squeeze the operating lever. This action pushes the actuating rod, which presses down on the spring-loaded valve, opening the passage to the nozzle. The bottom of the rod features a sharp point that punctures the gas cylinder release valve.
The metal safety pin is designed to prevent the operating lever from being accidentally activated.
The operating lever presses down on an actuating rod (the blue component).The release of compressed gas creates downward pressure on the fire-suppressant substance, pushing it up through the siphon and out of the nozzle with great force.
How to Operate a Fire Extinguisher
The correct technique for using the extinguisher is to aim at the base of the fire, targeting the fuel rather than the flames themselves, and sweep the stream from side to side.
Different Types of Portable Fire Extinguishers
There are various types of fire extinguishers, each categorized based on the extinguishing agent they use. Understanding their differences will help you select the right one to ensure your family's safety.
Water-Based Extinguisher
Water is one of the most commonly recognized and effective fire suppression agents. However, it can be hazardous if used incorrectly. A water extinguisher is effective for fires involving wood, paper, or cardboard, but it should not be used on electrical fires or fires involving flammable liquids.
During an electrical fire, water can conduct electricity, potentially leading to electrocution. Additionally, water will only spread a flammable liquid, which can exacerbate the fire.
Carbon Dioxide Fire Extinguisher
A widely used fire extinguisher is the carbon dioxide type. In this extinguisher, carbon dioxide is stored as a pressurized liquid within the cylinder. When the extinguisher is activated, the liquid expands and turns into gas.
Carbon dioxide is denser than oxygen, allowing it to displace the oxygen around the burning material. This type of extinguisher is particularly common in restaurants since it won't contaminate food or cooking equipment during kitchen fires.
The discharge horn on a carbon dioxide extinguisher can become extremely cold, so it’s important to avoid touching it.
Dry Chemical Fire Extinguisher
The most commonly used fire extinguisher agent is dry chemical foam or powder, usually made from sodium bicarbonate (baking soda), potassium bicarbonate (very similar to baking soda), or monoammonium phosphate.
Baking soda begins to break down at just 158 degrees Fahrenheit (70 degrees Celsius), releasing carbon dioxide as it decomposes. The carbon dioxide, combined with the insulating properties of the foam, helps to put out the fire.
Fire Extinguisher Ratings
Fire extinguishers are classified based on the types of fires they are capable of extinguishing.
- Class A extinguishers are effective against fires from "ordinary combustibles" like wood, plastic, or paper.
- Class B extinguishers can handle fires from flammable liquids such as gasoline or grease.
- Class C extinguishers are designed for electrical fires. Extinguishers marked with A, B, and C are versatile enough to handle all types of fires.
- Class D extinguishers are specialized for extinguishing metal fires and are less common. Check the labels on your extinguisher to understand what types of fires it can address.
When to Contact the Fire Department
Fire extinguishers typically hold a limited amount of fire-suppressing agent, often enough to last only a few seconds. Because of this, they are most effective for controlling small, contained fires.
For larger fires, more substantial equipment is necessary — such as a fire truck — along with trained professionals to operate it. However, for the unexpected fires that can occur at home, a fire extinguisher is a critical lifesaver.
