What is the orange/red stuff that planes drop when fighting fires?
Wildfires are serious concerns wherever they occur, particularly in the western states, where the fire can spread quickly over hundreds of acres of trees with the right conditions. In some cases, firefighters and even planes loaded with water cannot dump water on all areas of a large fire, to keep it from spreading. This is where flame retardants come in. Firefighters have learned that dumping water on unburned trees or vegetation does not make it unburnable, especially in very hot fires, because the water simply evaporates. This is where flame retardants come in. Flame retardants do stop the spread of fire when they are applied at the barrier of a fire (around it or ahead of it). What are these flame retardants and how do they work?
You may have seen videos of planes dropping orange or red liquid over land. This liquid is usually a product called Phos-Chek ... which is sold by a company called Perimeter. Phos-Chek has been used for decades by the US Forest Service, however they have recently switched to a formula that is less toxic to aquatic life. The main ingredients of Phos-Chek are water and ammonium phosphate fertilizer, which unlike ammonium nitrate (the type of fertilizer used in explosives), actually works to deter burning. Under normal conditions, cellulose in plant matter decomposes as it's heated, producing flammable compounds. Phos-Chek's maker says the reaction between the retardant and cellulose consumes heat energy from the approaching fire and produces non-flammable carbon material. (What is the flame retardant that planes are dropping on the LA fires?) The red color is actually “rust” or iron oxide that is added to help the pilots see where the retardant has been applied, in order to make an unbroken line of defense. Once it’s on the ground or on vegetation, the water evaporates, but the salts remain to do their job. The iron oxide also stays behind for weeks or months.
The US Forest Service says that Phos-Chek should not be dropped within 300 feet of any body of water, so that it doesn’t become concentrated in the water and harm aquatic life, but if faced with the decision between saving lives and property or applying the retardant closer than 300 feet from water, it sometimes chooses the former. (Let Me Explain: Phos-Chek Debate | NBCLA)
Australia is a wildfire hotspot, sometimes seeing fires that consume 160 acres per minute (such as the Pinery bushfire in 2015). These fires that spread quickly across open fields are fueled by plant stubble, which is the residue of crops left over from the last harvest. Stubble is left behind to prevent erosion, and is a main practice of environmentally friendly no-till farming. However, crop stubble is a fuel that can sustain these explosive fires. Application of ammonium polyphosphate does two things: depending on the dosage, it can prevent complete consumption of the stubble, thereby slowing the fire and slowing erosion afterwards, and may act as a fertilizer during the next growing season. (SANTFA: First look at fertiliser as Flame Retardant)
But what about toxicity for humans? In liquid or powder form, ammonium phosphates can be skin and eye irritants. They are also dangerous to inhale in powder form. That’s why fire retardant formulas often include a thickener or gummy substance that can help it stick to vegetation once the water has evaporated. As a precaution, people walking through areas where it’s been sprayed should wear a particle respirator, however, the worst particles would be coming from burned or partially burned vegetation and structures (soot), not from the flame retardants.
For now, these types of flame retardants, and fire-resistant building practices, are our best protection when faced with more frequent wildfires, and if you live in an area prone to wildfires, may see them being dropped from the sky. According to the experts, the fire retardants are safer than the smoke particles and noxious gases, so in some cases it seems one is necessary to avoid the other.
Photo by Egor Vikhrev on Unsplash
