The Mechanism and Performance of Combustion Modified Flexible Foams in Small Scale Fire Tests

The subject of the behaviour of flexible polyurethane foams in a "fire situation" has always been a controversial issue. The introduction in March 1989 of legislation in the United Kingdom requiring all furniture and bedding sold to contain filling materials meeting BS 5852 has led to a complete new grade range of flexible foams. Currently these Combustion Modified High Resilience (CMHR) Foams are, in the main, based on "polymer polyols" or "grafted polyols" and contain Melamine as the major fire retardant additive. Some conventional fire retardant of the phosphorus-halogen type is also in cluded in the formulation. Samples of CMHR foams typical of those available on the European market have been evaluated in small scale fire tests, and their performance used to ob tain "targets" or "yardsticks" for further work. A Limiting Oxygen Index of 25% vol. O ₂ appears to be typical for these CMHR foams of density 25 kg/m ³ . We have shown that the combination of melamine and a phosphorus-halogen fire retardant is superior to that of either additive used singly and that the choice of the base polymer polyol also appears to have an influence on the per formance of the final foam. Both the PHD and PIPA polyols require less fire retardant additive than the SAN polyol, Polyurax U.1408, to achieve the same performance in the particular tests used. However these advantages are less obvious at higher fire retardant loadings. Of the potential alternatives to melamine screened in this evaluation urea appears to be the most obvious candidate. Foams containing urea were superior to those based on melamine in all the fire tests used. As an example an increase of about 2% vol. O ₂ requirement in the LOI test was obtained. Additives such as alumina trihydrate, magnesium hydroxide, ammonium polyphosphate and ammonium borates were not as effective as melamine in im proving the fire properties of the CMHR-foams. They did not interact benefi cially with the polymer, nor did they volatilise/decompose over the required temperature range.