The Behaviour of Commercially Important Diisocyanates in Fire Conditions Part 2: Polymeric Diphenyl Methane-4,4’-diisocyanate(PMDI)

Abstract

The behaviour of polymeric diphenyl methane-4,4’-diisocyanate (PMDI) is described when examined in a laboratory small-scale test for its reaction to fire (ease of ignition; heat release and toxic gas production). Full-scale real fire scenarios have also been staged to predict events if (1) drumstock PMDI and (2) sizeable pools of liquid PMDI become enveloped in a fire. PMDI requires a stimulus (e.g. heat) before it will ignite from an applied flame. It then burns in a self-sustaining manner for a few minutes, during which main emissions take place. Then a polymerization reaction begins, producing a low density non-burning residue, which progressively dampens down the burning events by blanket action. Residues of 30–80% sample weight were recorded. The major toxic gas produced is carbon monoxide, though free isocyanate is to be expected in the early stages of the fire, and hydrogen cyanide could be important, especially in well-developed fire conditions. Firefighters should therefore wear full protective clothing and fresh-air breathing equipment. Events when drums of PMDI are exposed to fire depend heavily on the characteristics of the containers, with some rupture steps proceeding with considerable violence. Drumstock PMDI should be stored separately from easily ignitable materials.