Impact of wood fire load on toxic emissions in ventilation controlled compartment fires

Toxic emissions from ventilation controlled compartment fires were measured for a 1.6 m³ enclosure with imposed air ventilation conditions of 11 air changes per hour (ACH), which was the lowest ventilation at which the fire would not self extinguish. The fire load was pine wood cribs and the influence of the fire loading or size of the cribs were investigated. The cribs were of constant height and the loading was increased by making the crib sticks longer, with increased number of sticks as the spacing between the sticks was kept constant. The fire loading was from 0.9 – 6 kg/m³, which is representative of realistic fire energy loadings on a compartment volume basis. The low 11 ACH ventilation for the highest fire load was a three hour fire. There were two stages to the fires. At low fire load there was an initial flaming fire that lasted about 20 minutes and at low fire load burned all the fire load and had the peak fire toxicity. This was a locally rich burning fire that did not involve all the air supplied to the compartment, but had the highest toxicity. For higher fire loads this initial burning phase was less intense due to the heat sink of the larger wood mass, but after the mean ceiling fire temperature reached 500ºC there was a flashover which occurred about an hour after the start of the fire. The highest toxicity then occurred after the flashover condition. For deaths in the fires (LC₅₀) CO and formaldehyde were the most toxic gases, but for impairment of escape (COSHH₁₅min) acrolein was the most important toxic gas with formaldehyde next.