So....when airplanes drop that red liquid on forest fires....what is that stuff anyway? It's called fire retardant, but what's it made of? How does it stop fires? Does it hurt the environment? Is it poisonous? What if it gets on people? Does it wash off? I fought forest fires for fifteen years and got drenched with the nasty red stuff several times, but never completely understood what it was. I decided to find out.
Fire retardant consists of 5 parts water and 1 part ammonia based fertilizer, clay thickener and coloring. The red color helps pilots see what areas have been covered. Salt levels are also controlled to keep the liquid at the correct thickness.
The actual chemical composition of fire retardant (originally called borate because of the presence of borate salts in the compound) has changed in recent years. Studies done on the toxicity of retardant on aquatic organisms revealed that one of the common ingredients in the mix, (sodium ferrocyanide), released cyanide into the environment when exposed to ultraviolet rays. As a result of these tests, the US Forest Service called for the discontinuation of retardants containing sodium ferrocyanide. The current retardant used is non-toxic to animals, but I can vouch that it doesn't do wonders for the complexion or hair.
The idea behind dropping retardant on a fire isn't to actually put the fire out. Retardant is meant to create a barrier that will slow and cool the fire enough to allow firefighters to attack it directly. The clay and salt thickening agents keep the slurry sticky enough to cling to whatever it is dropped on. The coated fuel doesn't burn well, so the fire slows. After the fire is over, the red residue can be washed off by winter rains or homeowner's hoses. The fertilizer in the mixture is intended to help new growth get established in burnt areas.
This stuff isn't cheap. Retardant sells for about $800 a ton. An air tanker can drop ten tons of retardant on a fire in one pass. The cost for the plane, pilot, and crew is around $1,400 per hour. Fighting fire from the air can be effective, but very expensive.
http://www.specialchem.com/TechCenter/flame_retardants_zinc_borate/index.asp
http://www.azcentral.com/news/articles/0627Fire-mesaplanes27.html
http://www.cerc.cr.usgs.gov/pubs/center/pdfDocs/summary_frc.pdf
http://www.signonsandiego.com/news/northcounty/20020212-9999_1n12tankers.html
http://www.fs.fed.us/r2/sanjuan/bulletin_board/Missionary%20Update21.htm