• Los Angeles is covered in pink dust: it is a fire retardant spread to contain the blazes.
• It is an industrial product that has been widely used for decades.
• Some studies suggest it contains heavy metals, but the company maintains it has passed rigorous safety tests.

The Los Angeles of this January 2025 bears no resemblance to the images we were used to seeing. The vast California wildfires have disfigured it, reducing thousands of buildings to shapeless piles of debris and ash – an update from 13 January reports 12,000 properties destroyed, 24 people killed and 100,000 displaced. There is one detail that cannot go unnoticed in these images: homes, land, cars and forests across Los Angeles coated in a pink dust. Here is what it is.

What the pink dust spread across Los Angeles is used for

The pink dust scattered everywhere across Los Angeles goes by the trade name Phos-Chek and is manufactured by Perimeter Solutions, a company headquartered in St. Louis, Missouri. In use in the United States since 1963, Phos-Chek is the most widely used fire retardant in the world. Essentially, it is spread over vegetation and terrain around a fire in order to limit the availability of oxygen and slow the spread of the flames.

Phos-Chek is available in multiple formulations – more or less viscous, liquid or powder – depending on whether it is to be deployed from aircraft, helicopters or tanker trucks. As an industrial preparation, its exact formula is not in the public domain; however, the company has previously disclosed that it is composed of approximately 80 per cent water, 14 per cent fertiliser salts and 6 per cent dyes and corrosion inhibitors.

BBC World Service @bbcworldservice

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Why the dust used to slow fires is pink

This fire retardant is pink in order to assist the work of firefighters, who can instantly identify the areas where it has already been applied. After a few days of sun exposure, it tends to fade on its own. Once the state of emergency is over, the manufacturer advises removing any Phos-Chek residue as quickly as possible using warm water and a mild detergent (or a pressure washer for larger surfaces). The longer this is left, the greater the likelihood that traces will remain.

AFP News Agency ✓ @AFP

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What is the pink stuff coating fire-ravaged Los Angeles?

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Is the fire retardant dangerous?

An article in the New York Times attempts to investigate the potential environmental and health risks of this pink dust, especially when the quantities involved – as in the case of Los Angeles – are so enormous. The answer is not straightforward.

A recent study shows that fire retardants contain metals (vanadium, chromium, manganese, copper, arsenic, cadmium, antimony, barium, thallium and lead) in quantities far exceeding the toxicity thresholds set for drinking water and, potentially, for release into natural environments as well. The researchers calculated the quantity of toxic metals left in the environment across the United States as a result of Phos-Chek and similar products: the total amounts to 380 tonnes. And it is reasonable to assume that, as wildfires become ever more frequent and destructive due to the climate crisis, the use of fire retardants is also set to increase. It is nonetheless true that wildfire smoke also poses a risk to human health: it is estimated that, globally, it contributes to 675,000 premature deaths every year.

Perimeter Solutions and the federal government, however, dispute this study, arguing that it refers to a different version of the product. A company spokesperson maintains that Phos-Chek has passed rigorous tests confirming its safety.