WHAT DO FLAME RETARDANTS DO?

Flame retardants are a tool that can have a favorable effect on every key fire property, including ignitability, flame spread, heat release, and ease of extinction; albeit they do not necessarily have all of these effects simultaneously in every case. Some examples follow associated with well-known products in actual use where the effectiveness of the appropriate flame retardant system has been well demonstrated or even incorporated into codes or regulations. It is not possible to assign a particular flame retardant to a specific application, since many different flame retardants can be used for a variety of applications and vice versa.

Wood behaves very differently if it has been treated with flame retardants to obtain fire-retardant-treated wood (FRTW). Standard wood panels tend to exhibit a flame spread index (FSI) of between 75 and 200 (in the ASTM E844 test), while FRTW panels exhibit an FSI of under 25 and are accepted in many more applications than standard wood panels.

Recent heat release work has shown that the peak heat release rate [in the cone calorimeter] for both low density and medium density particleboards decreases when flame is retarded.5 Similar results exist for larch and thermowood pine.6 In all the cases reported, the treated wood materials were also less easily ignitable.

Cellulose loose-fill is a product used for insulating attics, although it has relatively poor fire performance. Regulations and codes require the product to meet a critical radiant flux. This fire performance can only be achieved if the cellulose loose-fill is treated with flame retardants, often boron materials.

Cables installed in plenums have long been required by the National Electrical Code (NEC)7 to be encased in non-combustible raceways. In the 1970s, fire hazard assessments showed that cables could be used safely in plenums without raceways if they met flame spread and smoke release requirements in a specific fire test designed for the application.8

After this was implemented in the NEC, it was found that suitable fire performance for plenum cable insulation and jacketing materials could be obtained with materials treated with flame retardants (often multi-additive systems). Small scale9,10 and intermediate scale10,11 heat release tests were conducted on the materials in these cables and on the cables themselves; the tests showed a significant decrease in flame spread and heat release associated with the flame retarded materials as compared to the ones that were not flame retarded. These are the materials typically used to make the cables used in plenums, meeting NEC requirements.

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