The shocking pink fire retardant saving Los Angeles: what you need to know

While the Californian city is still being attacked by flames, firefighters are using an unusual weapon: PHOS-CHEK, a bright pink flame retardant. But what are the effects of this substance on the environment? Is it really safe?

Have you seen the dramatic images of wildfires raging across Los Angeles since January 7? Amid the flames and smoke, there’s an eye-catching detail you might have noticed: a shocking pink substance being sprayed from tanker planes. What the heck is it?

It’s PHOS-CHEK LC95, an ammonium phosphate-based fire retardant playing an important role in fighting the most recent wildfires engulfing California.

The substance is produced at a facility in Rancho Cucamonga, east of Los Angeles, and works by forming a fire-retardant barrier on vegetation that reduces the spread of flames and offers a crucial window for firefighters to act.

Why is it pink?

The color is not an arbitrary choice. “We tested every color of the rainbow, and pink was by far the most visible“, said Melissa Kim, the vice president of research and development at Perimeter Solutions, manufacturer of PHOS-CHEK. “And it’s cute, too!”

The bright color makes it certain that pilots can see where the retardant has been dropped and optimize its effectiveness. But what exactly is this “pink rain”?

Composition and how it works

PHOS-CHEK is primarily a fertilizer based on ammonium phosphate salts, such as ammonium polyphosphate. Unlike water, these salts do not evaporate rapidly and linger on vegetation longer. When PHOS-CHEK comes into contact with fire, the phosphates react with plant cellulose, forming a char that acts as a barrier to combustion.

Developed some 60 years ago, the formula for PHOS-CHEK has been continually improved to be more effective with less environmental impact. Today’s formulations, for instance, are designed not to leave permanent stains on homes or vehicles.

Yet, some continue to question the environmental impact PHOS-CHEK creates. A 2024 report entitled Metals in Wildfire Suppressants demonstrated that the chemical compound contains heavy metals such as chromium, cadmium, and vanadium. These metals may pollute water bodies and, consequently, cause damage to aquatic life. According to an estimate presented in this report, flame retardants have emitted into the environment about 850,000 pounds, or around 425 tons, of these chemicals since 2009.
effectiveness and controversies

Despite its utility, PHOS-CHEK doesn’t always prove to be an assured solution. Its effectiveness relates to the surrounding terrain slope, vegetation type, weather condition, and when ground crews available to act after it is dropped. For instance, Timothy Ingalsbee, a former firefighter and Executive Director of the nonprofit Firefighters United for Safety, Ethics, and Ecology said, “Aerial retardants are effective within a narrow range of conditions, and the windows of opportunity for those conditions are shrinking every year due to climate change.”

The use of PHOS-CHEK and other similar retardants remains controversial among environmentalists, authorities, and manufacturers. Firefighters point out the crucial role they play in saving life and property, while environmentalists want more research on their ecological impact and are promoting greener alternatives. There’s no scientific evidence they make any difference in wildfire outcomes. It’s like throwing money out of planes, except it’s toxic, and you can’t buy anything with it because it doesn’t work,” said Andy Stahl, Executive Director of the Forest Service Employees for Environmental Ethics.