Its fuchsia pink color almost stings the eyes. However, this powder covers tens of km2 of the Los Angeles region (United States), dropped by Canadairs in order to protect homes and property, but also to prevent the progression of the flames which have already ravaged more than 15,000 ha since January 7. This pink powder is called Phos-Chek, a product marketed for decades by the American company Perimeter, based in Missouri.
In the United States, Phos-Check has been favored in firefighting since 1963, and “is the main long-term flame retardant used by the California Department of Forestry and Fire Protection,” explains the BBC. . Globally, it is even the most used flame retardant product in the world in 2022, according to the Associated Press agency.
How does Phos-Chek work?
The product is marketed in the form of a powder. It must then be diluted in water before being dropped or diffused either by Canadair or by ground teams, on areas close to fires, whether vegetation or homes. Normally, only authorities trained in its use can use it in this form. A version in concentrated liquid form, easier to handle, is marketed for individuals.
The main components of this substance include ammonium polyphosphate, diammonium phosphate, diammonium sulfate, monoammonium phosphate, attapulgus clay, guar gum (or a guar gum derivative), and additives of performance kept secret by the company.
According to Perimeter’s website, a surface treated with Phos-Check “transforms into a non-flammable carbon” when it comes into contact with a flame, “which slows and prevents the spread of fire.”
Why is it pink?
Obviously, what catches the eye is the firecracker pink color of the powder. A nuance that owes nothing to chance: it allows firefighters to quickly see which areas have been treated or not and to act accordingly. By observing the parts affected by Canadair, the ground teams can then disperse the product in a more appropriate way.
“We tested all the colors of the rainbow and pink was by far the most visible,” Melissa Kim, vice president of research and development at Perimeter, told NBC Los Angeles in 2023. “If you can’t see it, it’s not effective. When flying over an area with thick smoke, little visibility and wind, pilots must be able to successfully release the first time, they do not have a second chance,” she further explained.
The pink color, caused by the presence of iron oxide in the powder, remains for several hours, then turns to an earthy brown after a few days of exposure to sunlight. The company therefore advises removing it “as soon as possible” from covered surfaces, by cleaning the product with soap and water. “The longer the retardant dries, the more difficult it is to completely remove it,” the company warns.
A product with controversial effects
Phos-Chek, due to its chemical composition, is not exempt from any suspicion of negative effects on the environment. The Forest Service Employees for Environmental Ethics, an organization made up of current and former employees of the US Forest Service, in 2022 accused the US federal forestry agency of violating the nation’s clean water laws by dumping fire-retardant chemicals from airplanes into forests. According to the association, the chemical kills fish in affected waters and is not effective.
The case caused a lot of noise in the United States, especially when justice ruled in favor of the organization in 2023, but authorized the product to still be used, in view of the agreement obtained from the agency. American federal environmental protection agency. It is also prohibited to spread Phos-Chek or any other chemical retardant in protected areas such as watercourses or those where protected species live. But an exception exists, in cases where “human life or public safety are threatened”.
Similar retardants are used in France in the event of a large fire, with iron oxide to make the substance visible. Ammonium polyphosphate is again the main component, but unlike the United States, the products used in France are tested and validated by the Entente for the Mediterranean Forest Test and Research Center ( Ceren).
