To tackle several large wildfires raging in the Los Angeles area, officials are deploying a bright red fire retardant. This dramatic substance has created eye-catching scenes as it blankets houses, vehicles, and roads.

As big aircraft spread this retardant over Southern California, social media is awash with questions regarding its makeup, purpose, and ecological effects.

This type of long-lasting fire retardant has been a key part of firefighting strategies for more than 50 years. Though it is approved by the U.S. Forest Service, the organization has placed restrictions on using it in federal lands near water or endangered species habitats unless human lives or critical infrastructure face imminent danger due to environmental concerns.

Here’s what we know about this fire retardant:

What is in the fire retardant?

The unique red fire retardant, known as Phos-Chek, has been employed by wildfire responders for over 50 years, as indicated by its manufacturer, Perimeter Solutions.

Federal data shows that from 2009 to 2021, more than 440 million gallons of this long-term fire retardant were dispensed across federal, state, and private lands, primarily in the western U.S.

The core ingredients of these long-lasting fire retardants mainly consist of salts, typically derived from agricultural fertilizers. These salts “alter the combustion process, lessen fire intensity, and slow fire progression,” according to the U.S. Department of Agriculture Forest Service.

These mixtures incorporate water and can be delivered in both liquid or granular forms, depending on what emergency teams require.

Why is fire retardant colored red?

The bright red color of the fire retardant comes from iron oxide, often referred to as rust.

This dye is added to ensure the retardant is easily visible from the sky, allowing firefighters and ground personnel to monitor where it has been applied.

The USDA notes that the iron oxide will gradually fade, losing its color “due to weathering, rain, or various environmental factors.” Typically, it is expected to fade within a few months.

How does fire retardant function?

The long-term fire retardant is frequently used to redirect wildfires and protect crucial locations or neighborhoods. When flames draw near, it sparks a series of reactions.

Upon heating, the retardant’s components prevent the cellulose in plants from fueling the fire, according to Perimeter Solutions. As it breaks down, it releases water vapor, effectively “cooling the flames” and depriving them of fuel.

This leaves behind a charred carbon residue that “insulates and limits airflow to any remaining fuels,” as stated by the manufacturer regarding its application. “Consequently, the intensity of the diminished fire is lessened, making it significantly easier to manage.”

Is fire retardant safe to use?

Phos-Chek has been approved by the USDA after passing tests that confirm it adheres to environmental safety standards, as indicated by both the government and its manufacturer. It also does not contain any substances linked by the state of California to “cancer, developmental, or reproductive risks.”

“They are the safest, most effective, and eco-friendly products available,” claims Perimeter Solutions on its website.

However, the USDA requires a minimum distance of 300 feet between the application of long-term fire retardants and the edges of waterways due to concerns for aquatic organisms. The agency does allow exceptions in cases where fire threatens “life or property” and “the potential damage to natural resources surpasses the risks to aquatic ecosystems,” as detailed in an environmental impact report by the USDA.

Additionally, any “incursion” must be reported, assessed, monitored, and “addressed as necessary.”

Recent research from the University of California, Los Angeles, indicated that long-term fire retardants might contain harmful heavy metals. However, Perimeter Solutions, the maker of Phos-Chek, has consistently disputed the findings of this research.