Smoke toxicity of fire protecting timber treatments

Abstract

Most fire deaths arise from inhalation of toxic gases. The fire toxicity of untreated plywood, pressure impregnated plywood and surface coated plywood was investigated under a range of fire conditions. Using the steady state tube furnace individual fire stages were replicated, fire effluent sampled, and toxic product yield determined by high performance ion chromatography and spectrophotometry. Despite different phosphorus loadings, both treatments hindered developing fires with less than 50% mass loss during non-flaming oxidative pyrolysis and did not readily undergo steady flaming. During under-ventilated flaming, all samples produced hydrogen cyanide (HCN), and both fire protecting treatments produced phosphoric acid (H3PO4). Assessment of smoke toxicity as fractional effective dose for incapacitation was based on asphyxiants carbon monoxide (CO) and hydrogen cyanide (HCN). This work demonstrates that due to emission of large amounts of CO, the predicted smoke toxicity of impregnated timber is significantly higher than coated timbers when a growing fire reaches the under-ventilated stage. The results have clear implications for those selecting products to ensure fire safety in enclosures such as buildings.