Fire Extinguisher : 101

How Fire Extinguishers Work

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Flames need fuel, oxygen and heat in order to burn. Fire extinguishers are designed to remove one of these elements by applying an agent that either cools the burning fuel, or removes or displaces the surrounding oxygen. You can read more details on fire extinguishing agents here.

Fire extinguishers contain either water or a smothering material, such as CO2. By pulling out the safety pin and depressing the lever at the top of the cylinder, the fire extinguishing material is released under high amounts of pressure.

How Fire Extinguishers Work
At the top of the cylinder, there is a smaller cylindrical container filled with compressed gas. A release valve acts as a locking mechanism and prevents this gas from escaping. When you pull the safety pin and squeeze the lever, the lever pushes on an actuating rod that presses the valve down to open a passage to the nozzle. The compressed gas is released, applying a downward pressure on the fire-extinguishing material, and pushing it out the nozzle under tremendous force.

Although the temptation is to aim the extinguishing material at the flames, the proper way is to aim it directly at the fuel.

Water Extinguishers
Water extinguishers are filled with regular tap water and typically pressurized with air. The most common way to remove heat is to spray water on the fire; however, depending on the type of fire, this approach is not always the best option.

Dry Chemical Extinguishers
Dry chemical extinguishers are filled with foam or powder, usually potassium bicarbonate or sodium bicarbonate (baking soda), and pressurized with nitrogen. Baking soda is effective because it decomposes at 158 degrees Fahrenheit and releases carbon dioxide, which smothers oxygen once it decomposes. Dry chemical extinguishers interrupt the chemical reaction of the fire by coating the fuel with a thin layer of powder or foam, thereby separating the fuel from the surrounding oxygen.

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• The type of flammable metal you are dealing with determines which type D fire extinguisher you will require.
• Copper extinguishing medium should be used when you are dealing with lithium and lithium alloy metals.
• Sodium chloride extinguishers should be used when you are dealing with magnesium, sodium, potassium, uranium and powdered aluminum.

Carbon Dioxide (CO2) Extinguishers
CO2 extinguishers contain carbon dioxide, a non-flammable gas. They are so highly pressurized that it is not uncommon for bits of dry ice to shoot out. Since CO2 is heavier than oxygen and very cold, it displaces or removes oxygen from the surrounding area and cools the fuel.

Do not forget that fire extinguishers require care and maintenance in order to remain functional!

Read more on different fire extinguisher types here.