The correlation between carbon monoxide and hydrogen cyanide in fire effluents of flame retarded polymers

Abstract

This study considers the demonstrated correlation between carbon monoxide and hydrogen cyanide in the special case of fire retarded materials. It shows that the combination of aluminium phosphinate and melamine polyphosphate causes a much smaller increase in the carbon monoxide (CO) and hydrogen cyanide (HCN) yields than the combination of brominated polystyrene and antimony oxide, although both fire retardants inhibit combustion reactions in the gas phase. The formation and destruction mechanisms of CO and HCN are considered. It is shown that both toxicants form early in the flame, and that the OH radical is critical for the destruction of both CO and HCN. Crucially, in the context of the flame inhibition mechanism, this suggests that the phosphorus system reduces the H and O radical concentrations without a corresponding decrease in the OH radical concentration, thus it is an effective gas phase flame retardant which only causes a small increase in the toxic product yields. Conversely, the bromine system reduces the H, O and OH concentrations, and thus increases the fire toxicity, by inhibiting decomposition of CO and HCN. Moreover, while the phosphorus flame retardant is effective as an ignition suppressant at low temperatures, this effect-switches off‖ at higher flame temperatures, minimising the potential increase in fire toxicity, once the fire develops.

Flame retardants in UK furniture increase smoke toxicity more than they reduce fire growth rate

“…The ChFR sample produced the highest yield of CO, followed by the UKFR sample, showing the effect of gas-phase free radical quenchers (like TCIPP, DBDPE and BDE-209) that inhibit the conversion of CO to CO 2 by reducing the concentration of the OH· radical 28 . The HCN yields, which generally increase in proportion to CO yields 34 , show the same effect of being enhanced by the presence of a gas-phase flame retardant 40 , but are relatively low, as would be expected from a well-ventilated test.…”

“…Data from large scale fires 31,32 in enclosures show much higher levels of both asphyxiant gases CO and HCN under conditions of developed flaming than those from small, wellventilated tests, such as the cone calorimeter 33 (ISO 5660). For a particular material, under different fire conditions, the HCN yield has been shown to rise proportionately with the CO yield 34,35,36 .…”

Fire toxicity – The elephant in the room?

“…For many hydrocarbon polymers, CO yield increases rapidly with increase in almost independent of polymer [32]. In addition, a close correlation between CO formation and HCN formation has been established in full-scale fire studies [33,34], as the formation of both species appear to be favourable under the same poorly ventilated fire conditions.…”

Flammability properties of polyvinyl alcohol containing new flame retardant system

“…synergistic effect between G/AFS/AN to enhance the flame retardancy of PVA. This may be referred to formation of char layer which containing polyaromatic structure, Al2O3, Fe2O3 and graphite that are chemically interacted and prevented the polymer from the effect of flame [27][28][29][30][31][32][33][34][35][36][37].…”