Triphosphate: a controversial but essential patron saint of safety

On July 6, 2013, Asiana flight 214 crashed when it landed in San Francisco, its fuselage caught fire and emitted thick smoke. In this accident, although the plane caught fire, the vast majority of passengers survived smoothly. It is a kind of chemical product widely existing in our life, but often ignored, that is flame retardant.

The wreckage of Hana flight 214. Photo from: Wikipedia

As a conventional means of fire prevention, flame retardants are widely added to a variety of materials. However, the question about flame retardants, especially brominated flame retardants, has never stopped. Many people believe that flame retardants do not play a very important role in fire protection, they will spread in the environment and endanger human health. Is that the case?

Flame retardant, the invisible patron saint of life

Flame retardant is a kind of additives which can delay the ignition time and inhibit the spread of fire. They inhibit the occurrence of combustion reaction through a variety of action principles. Inorganic flame retardants such as aluminum hydroxide and magnesium hydroxide generate water when heated, which absorbs a large amount of heat in the process, and also plays the role of isolating oxygen; brominated flame retardants can capture the free radicals in the combustion reaction and terminate the occurrence of chain reaction; in addition, some flame retardants can make the surface of materials rapidly expand and carbonize to form a protective layer.

From plastic products, synthetic leather, chemical fiber fabrics to foam insulation materials in buildings, there are polymer materials everywhere in our lives. These materials have many advantages in performance, but there is an obvious defect: they are easy to burn, thus burying a fire hazard. In order to eliminate the hidden danger, it is necessary to use flame retardant to improve the fire resistance of materials.

Today, flame retardants are mainly used in transportation, electronic and electrical equipment, furniture and building materials. Adding flame retardants does not make the material fully resistant to fire, but it can still reduce the occurrence of fire and provide valuable escape time for people trapped in the fire. In the fire space, due to the accumulation of flammable gas and heat, the phenomenon of "flashover" may occur - all kinds of flammable materials are on fire at the same time within 1-2 seconds. The emergence of flame retardant can effectively avoid this situation. Take the cathode ray tube TV with plastic shell as an example, if it is not flame retardant, the escape time left for people in case of fire is less than 2 minutes, while with the help of flame retardant, the escape time can be increased to more than 30 minutes [2].

The role of flame retardants in fire safety has been confirmed. According to the assessment of the European Commission, the use of flame retardants has reduced the number of fire deaths in Europe by 20% in the past 10 years [3]. The Greenstreet Berman study conducted by the British government in 2009 showed that since the promulgation of the fire safety regulations for furniture and interior furnishings, from 2002 to 2007, there were 54 fire deaths, 780 non fatal burns and 1065 fire accidents [4], and fire prevention treatment of furniture was inseparable from flame retardant.

In 2009, a fire broke out in CCTV cultural center, which spread rapidly, causing serious damage to the external walls. Among them, the important reason for the spread of fire is the unqualified flame retardant performance of the insulation materials in the outer layer of the building [5]. It can also be seen that flame retardant is not dispensable.

Flame retardant is very important to the fire safety of family. Video from: bromine science and Environment Forum (BSEF), China Flame Retardant Society

Brominated flame retardants: we hate it, but we can't do without it

Among the flame retardants, brominated flame retardants are the most widely used ones, and there are various controversies around it. Some brominated flame retardants do pose environmental and health risks, but the risks of the currently approved products are still acceptable under the reasonable use. Moreover, these brominated flame retardants do provide good properties that other flame retardants are difficult to completely replace. Zhou Zhengmao, Secretary General of China flame retardant society, said: we hate it, but we can't do without it.

Brominated flame retardants are a series of brominated compounds, including decabromodiphenyl ether, tetrabromobisphenol A, etc. HBr produced by brominated flame retardant can be directly involved in the chemical reaction of combustion and block the free radicals produced in the reaction. This direct action mode can produce high-efficiency flame retardant effect with a small amount of addition. At the same time, HBr gas with higher density can also isolate air. Now, brominated flame retardants are widely used in electronic equipment, upholstered furniture and building thermal insulation materials.

The doubts about brominated flame retardants mainly come from human health and environment. Brominated flame retardants may produce harmful substances during thermal decomposition. They may also release from materials and enter the ecological environment and food chain. So, how big are these risks?

Will brominated flame retardants increase fire "toxicity"?

Toxic gas is a major killer in fire, so will bromine flame retardant increase the release of toxic gas in the fire?

Some kinds of brominated flame retardants may produce toxic substances such as brominated dioxins under certain conditions (which will not be produced under daily use conditions). However, it should be noted that the combustion of flammable materials in fire will produce a series of toxic gases such as carbon monoxide and polycyclic aromatic hydrocarbons, which are not related to flame retardants. The proportion of brominated flame retardants in polymer materials is very small. They are not poisonous gases in fire