How does forest-fire retardant work? ?

Question

Why is it red or orange or yellow? It looks like it is more than just "water" or moisture....how much do the planes dump in a single pass? (Was watching a video on the California wildfires and wondered this) Is it bad for the environment? (Like a fire isn't bad...I know fires can be good as well but you know what I mean).

Answer 1

Ammonium polyphosphate liquids have been used as aerially applied fire- retardants.

Wildland fire retardants are generally applied aerially in a less than completely controlled manner. Due to the presence of variables such as vegetative cover, smoke, or wind drift that impact the trajectory of the free-falling solution, aerially applied wildland fire retardant solutions may land on or near people, animals and in bodies of water, or on soil where it could enter the water supply.  

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.