Los Angeles is dyed pink, like the end of the world? Are these pink substances harmful to the human body?

On January 13, 2025, pink "rain" fell from the sky in Los Angeles, USA, dyeing almost everything in some areas, including houses, cars, streets, and trees, pink, as if the world was about to end. This phenomenon has sparked heated discussions among netizens around the world on social media: What are these pink substances and are they harmful to the human body?

Image source: a social platform‍

In fact, this is related to the wildfire that occurred in southern California from January 7 to January 31, 2025. As of January 31, 2025, the wildfire has killed at least 29 people, forced more than 200,000 people to evacuate, and destroyed more than 18,000 houses and buildings.

To slow the spread of wildfires, helicopters dropped thousands of tons of a pink flame retardant from the sky. The pink flame retardant is a mixture of water and a powder concentrate called Phos-Chek , which is made by a US-based company.

Phos-Chek comes in a variety of colors, such as orange, red and pink, and its eye-catching colors let pilots and firefighters know where the retardant has been dropped. However, these colored retardants fade after a few days of exposure to sunlight and blend into the soil, not permanently staining the landscape.

So, how does this flame retardant work so well in extinguishing wildfires?

The principle of the dry powder fire extinguisher we are familiar with is to spray dry powder to cover the surface of the burning object, forming an isolation layer to prevent oxygen from coming into contact with the burning object , so that the combustion is extinguished due to lack of oxygen to support the combustion. The inorganic salt components in the dry powder, such as sodium bicarbonate and ammonium phosphate, will decompose under high temperature, making it impossible for the combustion to continue, thus achieving the purpose of extinguishing the fire. The principle of Phos-Chek is similar to that of a dry powder fire extinguisher.

Finished Phos-Chek flame retardants are usually dry powders or concentrated liquids and need to be diluted with water before use. | By Unknown author- wikimedia commons

Phos-Chek's main ingredients include ammonium polyphosphate, diammonium phosphate, monoammonium phosphate, guar gum, and other ingredients that are trade secrets. The proportions of the above ingredients vary depending on the formulation. Flame retardants slow the spread of fire by cooling and coating the fuel, consuming oxygen from the fire, and the phosphates in the flame retardant change the way the fuel burns. When the flame retardant is heated and decomposed, it leaves a black carbon coating that not only insulates but also restricts air flow to any remaining fuel , slowing the fire and buying time for firefighters.

Although flame retardants are very effective, they also have limitations.

For example, during the spraying process, strong winds can put low-flying aircraft at risk , and may also cause the flame retardant to not completely cover the surface of the object and dissipate with the wind, greatly reducing its effectiveness. Many people are also worried that Phos-Chek will harm fish and aquatic life and have long-term effects on soil, insects and microorganisms. For this reason, the U.S. Forest Service requires aircraft to avoid dropping flame retardants within 90 meters of waterways (ground drops must also avoid waterways).

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A 2024 study published in the journal Environmental Science & Technology Letters found that flame retardants contain heavy metals , including lead, arsenic and thallium. Researchers at the University of Southern California estimated that flame retardants released more than 400 tons of heavy metals into the environment between 2009 and 2021, exceeding California's hazardous waste limit levels.

However, the subject of this study is Phos-Chek LC95W, which was phased out by the Forestry Bureau in 2025. They used a new product, MVP-Fx, in this wildfire. Experimental data showed that Phos-Chek MVP-Fx is less toxic to aquatic organisms. The product description of MVP-Fx says "minimal irritation to the eyes" and "no irritation to the skin", but inhaling it may still cause respiratory irritation. In the future, with the advancement of technology, there may be better ways to prevent wildfires.

References

[1]https://www.bbc.com/news/articles/c93lqng957jo

[2]https://en.wikipedia.org/wiki/Phos-Chek

[3]https://www.livescience.com/planet-earth/wildfires/whats-in-the-pink-fire-retardant-being-dropped-on-la-and-is-it-dangerous

[4]https://pubs.acs.org/doi/epdf/10.1021/acs.estlett.4c00727?ref=article_openPDF

https://www.worldrecordacademy.org/2023/3/worlds-largest-pipe-organ-world-record-in-atlantic-city-new-jersey-423169

Planning and production

Source: Bringing Science Home (id: steamforkids)

Author: Ah Xian

Editor: Yinuo

Proofread by Xu Lai and Lin Lin