'Flame retardants (FR) are compounds that when added to manufactured materials, such as plastics and textiles, and surface finishes and coatings that inhibit, suppress, or delay the production of flames to prevent the spread of fire.' 1
Flame retardants are broadly classified into halogenated and non-halogenated flame retardants
What are halogenated flame retardants?
Bromine, chlorine, fluorine and iodine, are the elements in the chemical group known as halogens. Halogenated flame retardants act directly on the flame, the core of the fire. They are said to act “in the vapour phase”, meaning that they actually interfere with the chemistry of the flame. Chlorine (chlorinated) and bromine (brominated) are both used in this role, but brominated retardants have been the most effective.
• The use of brominated fire retardants in Europe is effectively coming to a close through pan-EU legislation such as REACH and RoHS or through the Stockholm Convention (the USA is not a signatory).
• In the US, some states have banned their use, but others continue to permit them. The tendancy however, is towards their replacement.
• The main construction materials affected are extruded polystyrene (XPS) and expanded polystyrene (EPS) insulation. The main halogenated retardant used used in these materials until recently was a brominated retardant called HBCD or Hexabromocyclododecane. This has been replaced or is shortly to be replaced in most products by compounds claimed to be safer.
Halogenated flame retardants in the environment
Flame retardants are found at increasing levels in household dust, human blood and breast milk, and wild animals. The chemicals are widely distributed in the outdoor environment with the highest concentrations in the Arctic and marine mammals.
Many halogenated flame retardants are found to be persistent, bioaccumalative and/or toxic (PBT).
‘Persistent’ means that the compounds do not break down into safer chemicals in the environment through time, probably, in the case of fire retardants, many years.
‘Bioaccumalative’ means that the compounds accumulate in plants and animals and become more concentrated as they move up the food chain.
Toxicity
Most research into the effects on human health of fire retardants has concentrated on brominated FR. Chlorinated fire retardants are currently considered ‘safer’.
Effects of brominated flame retardants:
• No acute toxicity
• Chronic toxicity
- Endocrine disruption effecting neurodevelopment and reproductive systems
- Immune suppression
- Carcinogencity
Recent history of flame retardants and public health
Here’s a short 2010 video of a TEDx talk presented by a Californian biochemist. It discusses how the general population became/become the unwitting guinea pigs for the live testing of flame retardant chemicals in familiar household goods and clothing. You probably know the story, but it hasn’t lost its power to shock. Nor is it an advertisement for continuing complacency.
Replacing brominated flame retardants
DOW Chemicals, producers of EPS and XPS and probably the insulation company most threatened by bans on brominated FR, has produced an allegedly safer alternative. “The new product has been extensively tested and has proven to maintain its flame retardant performance while having a more sustainable profile,” said Takahiro Sugiyama, President of DOW Kakoh.
The ‘butadiene styrene brominated copolymer’ is expected by the United States Environmental Protection Agency (U.S. EPA) to be ‘safer than HBCD’. ‘However…’ the EPA report adds ‘… this alternative is inherently persistent and its long-term behaviour in the environment is not currently known.’ (Editor’s italics)
The Stockholm Convention’s review committee says that, according to the industry hazard assessment, the substance ‘is persistent, but not bioaccumulative or toxic’.
Construction insulation materials and their flame retardants:
• XPS and EPS (extruded and expanded polystyrene)
HBCD is being phased out and replaced by the DOW-developed butadiene styrene brominated copolymer.
• PIR (polyisocyanurate)
The FR in PIR is TCPP (Tris (1-chloro-2-propyl) phosphate) representing 5% - 10% of material content. It is a non-brominated compound using chlorine and phosphorous as the active elements.
• Polyolefin foams (eg polypropylene (PP), polyethylene (PE))
Use non-halogenated, nitrogen and phosphorous-based FRs such as Alkyl Phosphonate and Amino-Ether HALS.
• Mineral wool (eg glass wool, stone wool)
Mineral wools are inherently fireproof
• Loose-fill cellulose
Sodium borate (20% of total content) is being replaced ammonium salts of inorganic acids with added biocide to replace the borate's effect on fungus and acarians.
A non-borate FR product being fire tested on loose fill cellulose insulation
• Hemp
Ammonium salts of inorganic acids
• Wool
Ammonium salts of inorganic acids
• Flax
Ammonium salts of inorganic acids
The future of flame retardants
A short video of chemists talking about their work to produce better and more environmentally sound flame retardants.
References
1 Wikepedia