Particle Size Distribution During Pine Wood Combustion on a Cone Calorimeter

There is current interest in the impact of particles in fire smoke on the toxic hazards in fires and on the health of fire fighters. The exposure of people in fires to PM is over 1000 times that in ambient air and the role of breathing high PM in fires in fire deaths and impairment of escape from fires is unknown, as there are very few measurements of particle mass and size in fires. The exposure period would typically be 30 minutes and longer for fire fighters. The cone calorimeter is a standard piece of laboratory fire test equipment for heat release and smoke production measurements, by obscuration. It has been adapted by the authors to enable the measurement of toxic gas species using a heated Gasmet FTIR. This was used alongside the Cambustion DMS500 particle size equipment to determine the particle size distribution. The FTIR measurements were made on the raw gas emissions from the chimney from the fire compartment and the DMS500 measurements were on the diluted exhaust on the cone calorimeter. The experiments were carried out with an air box around the test specimen to simulate a compartment fire with a fixed ventilation rate. The ventilation rate used simulated an air starved fire typical of the conditions in a modern energy efficient house. The cone calorimeter was operated at 35 MW/m2 radiant flux and the ignition delay was 29s. The HRR was 90 kW/m2 throughout the flaming combustion period. The combustion conditions were very rich with high CO and aldehyde emissions. The cone calorimeter dilutes the products from the chimney of the fire using ambient air and the dilution ratio was about 100 at the particulate measurement point. The particle size distribution showed a classic nuclei and cumulative mode distribution with the nuclei peak at 20nm and the cumulative mode peak at 200nm. There was a high 20nm peak during the ignition delay, indicating a vaporised aerosol of high MW compounds from the wood, which were analysed using the FTIR. 20nm Particles continued to be produced 1 x 1011/cc for the 1400s burning period of the pine wood samples and continued to be produced in the char burning phase. The 200nm cumulative mode particles were produced at 1 x 109 /cc throughout the flaming combustion and then fell to <1 x 108 /cc in the smouldering phase of the fire. The size distributions were quite different than those from biomass wood stoves and from modern diesels engines, although they had some similarity with old dirty diesels of the 1980s. The FTIR analysis showed a large peak in CO (4%) and THC (6%) at around 800 – 1200 s in the fire. There was no equivalent dramatic change in the particle number in this time period, other than a small fall in the number of 20nm particles and rise in the number of 200nm particles. This work shows that fine particle emissions are likely to be a strong health effect in fires, as they are much higher than in diesel exhausts.