Fire Extinguisher Types and Their Limitations

Posted on Apr 1, 2025 in Chemistry

1. Limitations of Foam Extinguishers

  • In electrical fires, water content poses a risk to personnel due to conductivity, especially in manual applications. Automatic systems are more effective than water alone.
  • Incompatibility between some foams and powder extinguishers can cause foam breakdown when applied simultaneously, particularly with obstacles on the burning liquid’s surface.
  • Not suitable for pressurized gas fires (butane, propane, etc.) due to high evaporation and swelling.
  • Reacts with highly reactive liquids that react violently with water or metals (e.g., sodium and potassium).
  • For liquid spill fires, use foam-compatible powder extinguishers or wait for fuel confinement before applying foam for effective extinguishing.

2. Types of Extinguishing Agents

Water

Water is the most abundant and economical extinguishing agent. It primarily extinguishes fires by cooling and can be applied as a stream or fine mist. Water jets should only be used on Class A fires.

Water spray can be used on Class A and Class B fires involving heavy liquid fuels like fuel oil and gas oil. Never use water on Class E (electrical) fires due to the risk of electrocution.

Carbon Dioxide (CO2)

Also known as dry ice or CO2, it’s an inert gas heavier than air, used to suffocate the fire. Effective for fires caused by flammable liquids. It’s also used on electrical fires as it’s non-conductive and leaves no residue.

Foam

There are two types of foam: chemical and physical (mechanical or air).

Chemical Foam

Formed by mixing an acid solution with a basic solution. The reaction produces carbon dioxide, increasing pressure and releasing fire-extinguishing foam. It extinguishes by cooling and suffocation.

This type of foam attacks metals, is electrically conductive, and dissolves in alcohol, making it less common today.

Physical Foam

A mass of bubbles joined by a stabilizer, applied as a blanket over the burning liquid to prevent or extinguish the fire by suffocation.

Foam is effective against Class B fires, except for water-soluble hydrocarbons like alcohols and acetone. It’s also effective on Class A fires when left on long enough to form a mantle.

Halogenated Agents (Halon Replacements)

Halogenated compounds or halon replacements extinguish fires by paralyzing the chain reaction. They are effective against Class E fires and acceptable for Class A and B fires.

The use of halons as fire extinguishing agents is decreasing. Products like FM200 are used as replacements.