Wood Crib with PVC Cables: Compartment Fire Toxicity

Electrical cable fires may occur as part of a fire load and this was simulated using a pine wood crib fire in a compartment with PVC cables laid as a single layer on top of the crib. The aim was to trace the HCL yield under a mixed fuel compartment fire. A 1.6 m3 compartment fire was used under fixed ventilation conditions. The 3.0 kg pine wood crib, with 0.25kg of 12 PVC cables 100mm long in a bundle placed in the centre of the crib, was burnt with 21 air changes an hour, simulating a restricted ventilated compartment fire. Toxic gases were measured using the Temet Gasmet heated FTIR, calibrated for 60 species including all the fire toxic gases. The HCl yields were similar to those in cone calorimeter tests for 40 kw/m2. The toxic gases were high during the flaming phase of the fire where the peak temperatures and peak heat release occurred. The long smouldering phase of the pine wood crib fire had low concentrations of toxicity. The fire toxicity was dominated by the toxic products from the wood fire and the HCL from the PVC fire was a minor contributor. However, in the PVC cable fire tests on the cone calorimeter it was found that the peak yield (per g of PVC) of acrolein and formaldehyde were 0.055 and 0.035, respectively and were the dominant toxic gases for PVC cable fires and hence the PVC cables would have contributed to the yields of acrolein and formaldehyde in the combined wood crib and PVC cable fire. For the wood crib alone the acrolein and formaldehyde peak yields were 0.008 and 0.014 g/g respectively. The present results show much higher yields and this is because of the significant contribution to their formation from the presence of the PVC cables. The role of PVC cables in acrolein and formaldehyde formation has not previously been recognised.