Recently, near my office was a wild fire, which was fought aerially using that red fire retardant. And it got me thinking, “how does the fire retardant work?”
I’ve heard there are 3 things required for a fire: fuel, heat, and oxygen. My first thought was that the fire retardant must smother the fire, but I quickly rejected that – any firefighter in the area could be asphyxiated if they got dropped on.
So how DOES that red fire retardant work? Which of the 3 factors does it affect? Or does it work on a combination? And by what mechanism does it “retard” the fire?
Thanks,
yabob
July 5, 2009, 6:22pm
2
Takes away fuel, basically. Explanation from one of the companies manufacturing the stuff:
http://phos-chek.com/products/retardant.php
Our wildland fire retardants consist of fertilizer type salts, a coloring agent, corrosion inhibitors, and flow conditioners. The salts, when heated by the approaching fire, react with the woody material, grass and other organic matter rendering it unburnable, thus retarding the fire spread.
Products like that use to use borates, but they don’t do that anymore. From wiki:
Borate salts were used in the past to fight wildfires but were found to sterilize the soil, were toxic to animals, and are now prohibited.[7] Newer retardants use ammonium sulfate or ammonium polyphosphate with attapulgite clay thickener or diammonium phosphate with a guar gum derivative thickener. These are not only less toxic but act as fertilizers to help the regrowth of plants after the fire. Fire retardants often contain wetting agents, preservatives and rust inhibitors and are colored red with ferric oxide or fugitive color to mark where they have been dropped. Brand names of fire retardants for aerial application include Fire-Trol and Phos-Chek.
Aerial firefighting, also known as waterbombing, is the use of aircraft and other aerial resources to combat wildfires. The types of aircraft used include fixed-wing aircraft and helicopters. Smokejumpers and rappellers are also classified as aerial firefighters, delivered to the fire by parachute from a variety of fixed-wing aircraft, or rappelling from helicopters. Chemicals used to fight fires may include water, water enhancers such as foams and gels, and specially formulated fire retardants s...
Also there is a 4th component, a chemical reaction, some fire retardants stop the fire by preventing that 4th component.