You know the images of the fires that have been devastating Los Angeles since January 7th? Among the flames and columns of smoke, you will surely have noticed an unusual detail: a shocking pink substance that is sprayed by tanker planes. But what is it?
It is PHOS-CHEK LC95, a flame retardant based on ammonium phosphate that is playing a fundamental role in the fight against the fires that have been keeping California in suspense for days.
This substance, produced in a factory in Rancho Cucamongaeast of Los Angeles, acts by creating a fireproof barrier on vegetationslowing the spread of flames and giving firefighters the opportunity to intervene.
But why pink?
It’s not a random choice. “We’ve tested every color of the rainbow and pink was by far the most visible“, he explained Melissa Kimvice president of research and development at Perimeter Solutionsthe company that makes PHOS-CHEK. “And it’s cute!”.
Aerial firefighting is playing a critical role in the battle against Southern California’s raging wildfires. Behind…
Posted by Perimeter Solutions on Saturday, January 11, 2025
The bright color, in fact, allows tanker pilots to see where the retardant has already been dropped, ensuring greater effectiveness in interventions. But what exactly is in this “pink rain”?
Composition and mechanism of action
PHOS-CHEK is essentially a fertilizer based on ammonium phosphate saltssuch as ammonium polyphosphate. Unlike water, these salts do not evaporate easily and remain on vegetation longer. When PHOS-CHEK comes into contact with fire, the phosphates react with plant cellulose, creating a carbon layer that prevents the fuel from catching fire.
The original PHOS-CHEK formula it was developed about 60 years ago and, over time, it has undergone several modifications to improve its effectiveness and reduce its environmental impact. Today, for example, there are formulations that do not leave permanent stains on houses and cars.
Despite its usefulness in fighting fires, PHOS-CHEK also raises some environmental concerns. A study entitled “Metals in Wildfire Suppressants”, published in October 2024, highlighted the presence of heavy metals in its composition, such as chromium, cadmium and vanadium. These metals can contaminate waterways and harm aquatic wildlife. The study estimates that since 2009, the use of flame retardants has released approximately 850,000 pounds (about 385 tons) of these chemicals into the environment.
Furthermore, the effectiveness of PHOS-CHEK is not always guaranteed. It depends on various factors, such as the slope of the terrain, the type of vegetation, the weather conditions and the presence of teams on the ground who can intervene after the release of the retardant. Timothy Ingalsbeea former firefighter and executive director of the nonprofit Firefighters United for SafetyEthics and Ecology, pointed out that “air retardant is effective under a narrow range of conditions, and the windows of opportunity for those conditions are narrowing every year due to climate change.”
The use of PHOS-CHEK and other flame retardants is the subject of heated debate among environmental experts, authorities and manufacturers. While firefighters stress the importance of these tools for protecting lives and property, environmentalists are calling for more studies on their environmental impact and the search for greener alternatives. Andy Stahlexecutive director of the environmental group Forest Service Employees for Environmental Ethicsstates that “there is no scientific evidence that it makes any difference in wildfire outcomes. It’s like throwing money off planes, except that it’s toxic and you can’t buy anything from it because it doesn’t work“.
