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Types of Fire Suppression Agents

Always consult local fire codes before implementing a fire suppression system. Your local fire marshal is an excellent expert source: experts always prefer to prevent a fire rather than extinguish one and are often generous with their time dedicated to preventive measures. Any rules of thumb mentioned in this text will be valid for the exam, but always check your local fire codes before implementing any of these controls.

All fire suppression agents work via four methods (sometimes in combination): reducing the temperature of the fire, reducing the supply of oxygen, reducing the supply of fuel, and interfering with the chemical reaction within the fire.

Exam Warning
Always consider “hire or ask an expert” as a valid choice for any exam question asking about “the best thing to do.” Do not fall for the engineer’s trap of “I will figure this out on my own.” That mindset may make for good engineers, but can lead to disastrous physical security decisions.

Water

Water suppresses fire by lowering the temperature below the kindling point (also called the ignition point). Water is the safest of all suppressive agents and recommended for extinguishing common combustible fires such as burning paper or wood. It is important to cut electrical power when extinguishing a fire with water to reduce the risk of electrocution.

Soda Acid

Remember those old giant brass fire extinguishers? They were about the size of a fire hydrant and weighed almost as much. They used soda acid, which is also how they were pressurized. The cylinder was filled with soda (sodium bicarbonate) mixed with water, and there was a glass vial of acid suspended at the top. When you wanted to use the fire extinguisher, you would break the vial via a lever (or pick the extinguisher up and slam it on the floor). This would break the glass vial and mix the acid with the soda water, creating a chemical reaction that would create gas (thus pressurizing the extinguisher).

In addition to suppressing fire by lowering temperature, soda acid also has additional suppressive properties beyond plain water: it creates foam that can float on the surface of some liquid fires, starving the oxygen supply.

Dry Powder

Extinguishing a fire with dry powder (such as sodium chloride) works by lowering temperature and smothering the fire, starving it of oxygen. Dry powder is primarily used to extinguish metal fires. Flammable metals include sodium, magnesium, and many others.