Smoke, CO2 and CO evolution from cotton and flame retarded cotton: Part 1. Behaviour of single layer fabrics under LOI conditions

The limiting oxygen indices of two different area densities of untreated and phosphorus-containing flame retardant cotton fabrics (Proban CC, Amgard TR, Amgard CD) have been determined at 20 and 100°C. Simultaneous smoke and CO evolutions from all the fabrics have been determined at respective LOI and (LOI + 0.010) oxygen concentration conditions at 20 and 100°C. At 20 ° C, flame retardants present greatly increased smoke generation whilst little if any change in CO generation (except for the bromine-containing Amgard CD) occurred. Whilst increase in temperature to 100°C reduced fabric LOI and increased apparent and specific smoke optical densities its effect on CO generation was not straightforward. Lightweight, bromine-free flame retarded fabrics showed increased CO formation whilst for the heavier fabrics, increased area density and/or presence of bromine stabilised or reduced CO evolution. Combustion product analyses were undertaken at elevated temperatures (225-300°C) in air under burning conditions (above the respective temperature oxygen index) and non-flaming pyrolysis. Under both conditions smoke densi ties and CO concentrations increased with temperature. Carbon dioxide con centrations under non-flaming conditions showed similar increases but under burning conditions, decreased with increasing temperature. At a given temper ature, the P- and N-containing retardants reduced smoke density under burn ing conditions and increased it under pyrolysis relative to pure cotton below 350°C. These same flame retardants reduced CO and CO2 formation at each temperature from burning fabrics but produced little change with respect to cotton under non-flaming conditions. The presence of aliphatic bromine in the Sb2O3—bromine synergistic system caused significant increases in smoke density and CO and CO2 concentrations with respect to all other fabrics under pyrolysis in air. The observed trends are analysed in terms of current knowledge of pyrolysis and combustion mechanism