Fire in L.A.: How does the pink fire retardant work?

When the infamous, hairdryer-like Santa Ana winds weaken, the devastating fires in the Greater Los Angeles area can be fought from the air.

To do that, firefighting planes and helicopters have dropped a pink fire retardant that extinguishes the flames or slows down their spread. It has left houses, gardens and streets glowing in a bizarre, bright pink.

Flame retardants, on the other hand, are used in construction materials, wall cladding, curtains, furniture, electrical appliances and floor coverings to protect against fire. These can include halogenated chemicals, like bromine and chlorine.

How do flame retardants work?

Both fire and flame retardants have chemical substances that delay the ignition of flammable materials, preventing or slowing down the spread of flames. They work due to both their chemical and physical properties.

During a fire, materials break down due to the heat — known as pyrolysis — and emit gases, many of which are flammable. Tiny reactive particles, called radicals, are responsible for sustaining the fire.

Retardants cause the gases to react with these radicals, neutralizing them. They stop the radicals' chain reactions, inhibiting their combustion and forcing the fire to either burn more slowly or not at all.

In addition, some retardants swell at high temperatures, forming a protective layer of charred material — called intumescence. This insulating barrier prevents oxygen and heat from reaching the burning material.

Retardants also trigger a process called endothermic decomposition, which cools the environment by absorbing heat. This also slows down the combustion process.

Why is the L.A. fire retardant pink?

Bright dyes made from iron oxide are added to fire-extinguishing water or agents, giving them their eye-catching pink or red color. 

This improves the visibility and effectiveness of efforts to fight wildfires. Firefighters and firefighting aircraft can more easily identify where extinguishing agents have been deployed. 

How is flame retardant made?

Common fire retardants, such PHOS-CHEK, which is used in Los Angeles, include fertilizers, such as ammonium polyphosphate, diammonium phosphate and diammonium sulfate, as well as monoammonium phosphate as a fire retardant, attapulgite clay and guar gum as thickeners. 

Other fire retardants, such as FIRESORB, contain polymer additives that can absorb many times their weight in water. This creates a thick protective layer on surfaces, providing long-lasting resistance to heat and flames. 

Do fire and flame retardants pose risks for human health?

In devastating fires, like those in Los Angeles, the deadly fire is clearly the main danger — the first priority is to stop the fires, any which way.

But the smoke and the toxic mixture of microscopic particles in the air are also dangerous. These particles can penetrate the lungs and bloodstream, causing respiratory and heart problems. 

In 2024, the Alzheimer's Association published a study showing that smoke exposure from wildfires has a much worse impact on the brain than all other types of air pollution. The risk of dementia increases significantly, according to the study.  

So, fire and flame retardants do make everyday life safer. However, the US National Institute of Environmental Health Sciences cites a growing body of scientific evidence that chemicals found in some retardants can be harmful to both animals and humans. 

Children are particularly vulnerable to the toxic effects of some retardants because their brains and other organs are still developing. 

Halogenated flame retardants, which typically contain bromine or chlorine, are considered especially harmful to the environment and human health. In fires, they release highly toxic dioxins and furans, which damage the nervous system and have been linked to cancer. 

In addition, some chemicals in flame retardants cannot be broken down in the environment and accumulate in the bodies of living organisms, traveling up the food chain. They have been detected in breast milk, fish, and other organisms, indicating a potential health hazard.

How do fire and flame retardants harm the environment?

Fire retardants containing phosphorus compounds leave large amounts of phosphates and chemical residues in soils and water systems. This can lead to eutrophication, an accumulation of nutrients, especially phosphates and nitrates, in the ground water. This can cause excessive algal blooms, which deplete oxygen from the water. 

According to a communications officer for Perimeter Solutions, who make PHOS-CHEK — the fire retardant used in the 2025 L.A. wildfires — it has been tested by the USDA Forest Service to ensure that it is safe.

However, it has been shown that when firefighters and local residents are exposed to excessive amounts of both smoke particles from a fire and a fire retardant at the same time — even one deemed safe — the combination can cause irritations in a person's airways and on skin. 

Researchers have also detected heavy metals in the environment after the use of fire retardants. Among these metals were chromium and cadmium, which are harmful to both human health and the environment.

This article was originally published in German. It was amended on January 23, 2025, to distinguish between fire retardants and flame retardants.