Flame Retardants: Toxicity and Effects on Environment

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Wildfires

Wildfires are common in summer. Image by John McColgan.

These days, firefighters use more than water hoses to fight fires – chemicals are at the forefront in the war on wildfires and domestic fires. Do flame retardants cause emissions of chemicals which could be toxic for humans and/or the environment?

Summer Fires: Common and Dangerous

Wildfires, like those taking place in California in the last weeks, are unfortunately a common occurrence in many US areas, as well as in other countries.

These fires can pose a serious threat to the ecosystem, as large areas of forests get burned. They can also be dangerous for the people living in the vicinity of the affected areas. Moreover, the smoke from the fires may contain dangerous chemical compounds.

Preventing Wildfires: the Use of Flame Retardants

Due to all the problems mentioned above, it is essential to try to stop the fires from starting in the first place. One of the key points in prevention is, of course, to increase the awareness of the general public, for them to avoid risky behavior which could accidentally cause wildfires.

Beyond this, however, it is common to use chemical compounds which can delay and/or inhibit the formation of the flames and, hence, prevent and/or diminish the spread of the fire. These compounds are called flame retardants.

Plane releasing flame retardants

This plane is releasing flame retardant chemicals. Image by Benchill.

Flame Retardants on Forests

Airplanes generally release flame retardants onto the forests from above. The retardant chemicals can be applied to the forests before any fires develop, as a prevention measure, and firefighters can also use them when a fire is already occurring, to help suppress the flames.

The most common retardants consist of a mixture of water (about 85 %) and inorganic chemicals (about 10 %), the remaining 5 % being constituted of coloring agents and stabilizers. The most common inorganic chemicals used are ammonium-based compounds, such as phosphates and sulfates of ammonia.

The retardants can act through different mechanisms; the ammonium solution, for instance, adheres to the surface of the vegetation and it can therefore retard the flames. Phosphate-based compounds, on the other hand, can react with some of the active species formed during the combustion (free radicals); in this way they inhibit the propagation of the flames.

Fire Retardants: Toxic for the Environment?

In recent years there has been an intense debate about whether or not these flame retardants pose a threat to the environment. In the past, all retardants contained sodium ferrocyanide as a corrosion inhibitor. However, due to its high toxicity, especially under UV irradiation, since 2007, firefighters do not use this compound anymore.

There are also other concerns with today’s chemical fire retardants. During combustion, for instance, toxic ammonia vapors may be liberated into the atmosphere.

Moreover, retardants can get into the aquatic ecosystem and cause problems to the flora and fauna of the contaminated areas. For example, scientists reported the negative effects on the development of salmon species due to high concentrations of flame retardants; in other cases a lethal effect was also observed on some trout species.

Flame Retardants in Our Homes

Further to the prevention of wildfires, manufacturers also use flame retardants in many objects present in our homes and that we use in our everyday lives. You may find flame retardants in electrical appliances, furniture, textiles, bedding, and more. Flame retardant chemicals are used as additives in the materials employed to make these objects.

The majority of retardants are halogen-containing organic species, i.e. organic molecules which have a chlorine or bromine atom; they are often used mixed with antimony oxide. Manufacturers add brominated polystyrene, for instance, to polyamides, the plastic materials used for electrical connectors.

Domestic fire.

Flame retardants can prevent domestic fires. Image by TPSDave.

Flame Retardant Chemicals: Possible Dangers?

Flame retardants are undoubtedly effective in preventing the development of domestic fires and, hence, their use has helped save lives. Some studies, however, showed that if a fire develops, the presence of halogenated flame retardants can make the emissions more toxic; therefore, the consequences for the people inhaling the emissions could be more serious.

Scientists reported that, for instance, in the case of polyamide with added brominated polystyrene and antimony oxide, the emissions in the event of fire contained higher quantities of carbon monoxide CO and hydrogen cyanide HCN, both asphyxiant / highly toxic gases.

Furthermore, there is also concern that these chemicals could accumulate in the environment and cause long-term damage.

Because of this, researchers are trying to develop alternative flame retardants which do not contain halogens; phosphate-containing organic compounds are a possible solution.

Flame Retardant Use

The use of flame retardants is essential to prevent accidents, both in our homes and for forests. At the same time, however, it is very important to assess the possible problems associated with their use; the risks include the emission of toxic chemicals and the long-term effect on the environment. It is, therefore, crucial to study the behavior of the retardants in the case of fires, and their interaction with the environment, to look for less harmful alternatives if necessary.

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