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Wet Chemical

Wet chemicals are primarily used to extinguish kitchen fires (type K fires in the US; type F in Europe) but may also be used on common combustible fires (type A). The chemical is usually potassium acetate mixed with water. This covers a grease or oil fire in a soapy film that lowers the temperature.

CO₂

CO₂, oxygen, and nitrogen are what we breathe as air. Fires require oxygen as fuel, so removing oxygen smothers fires: this is how CO₂ fire suppression works.

A risk associated with CO₂ is it is odorless and colorless, and our bodies will breathe it as air. By the time we begin suffocating due to lack of oxygen, it is often too late. This makes CO₂ a dangerous suppressive agent, which is only recommended in unstaffed areas such as electrical substations. Any personnel entering a CO₂-protected area should be trained for CO₂ safety; additional safety controls (such as oxygen tanks) are usually recommended.

Exam Warning
All environmental controls and safety procedures must ensure the safety of all personnel, including those with handicaps. Elevators cannot be used during a fire, for example, so employees in wheelchairs must have a compensating control.

Halon and Halon Substitutes

Halon extinguishes fire via a chemical reaction that consumes energy and lowers the temperature of the fire. Halon has been phased out for commercial use, and several replacements with similar properties are now used.

The chemical effect of Halon and Halon substitutes is often misunderstood: many believe they work like CO₂ and extinguish fire via oxygen starvation. While this is a secondary effect of Halon, this effect is comparatively minor: these systems are designed to allow enough oxygen to support human life.

Montreal Accord

Halon has ozone-depleting properties. Due to this effect, the 1989 Montreal Protocol (formally called the “Montreal Protocol on Substances That Deplete the Ozone Layer”) banned production and consumption of new Halon in developed countries by January 1, 1994. Existing Halon systems may be used. While new Halon is not being produced, recycled Halon may be used. There are exceptions for certain critical uses, such as airplanes and submarines. See https://ozone.unep.org for more information on the Montreal Protocol.

As a practical matter, Halon systems are no longer recommended due to their age. Any existing Halon system is probably over 20 years old and is likely due to be replaced due to sheer age. One option for replacement are similar systems such as argon or FM-200.

Halon Replacements

Recommended replacements for Halon include the following systems:

  • Argon
  • FE-13
  • FM-200
  • Inergen

FE-13 is the newest of these agents, and comparatively safe. It may be breathed in concentrations of up to 30%. Other Halon replacements are typically only safe up to 10–15% concentration.