Investigation on the emission of volatile organic compounds from heated vegetation and their potential to cause an accelerating forest fire.
Résumé
An experimental study is conducted on the emission of volatile organic compounds (VOCs) emitted by Rosmarinus officinalis plants when exposed to an external radiant flux. The thermal radiation heats the plant and causes the emission of VOCs. The thermal radiation simulates the radiant flux received by vegetation in a forest fire. The results of the experiments are used in a simplified analysis to determine if the emissions of VOCs in an actual forest fire situation could produce a flammable gas mixture and potentially lead to the onset of an accelerating forest fire. The experiments consist of placing a plant in a hermetic enclosure and heating it with a radiant panel. The VOCs produced are collected and analyzed with an automatic thermal desorber coupled with a gas chromatograph/mass spectrometer (ATD-GC/MS). The effects of the fire intensity (radiant panel heat flux) and the fire retardant on the VOCs emission are then investigated. Two thresholds of the VOCs emission are observed. The first is for plant temperatures of around 120C and appears to be caused by the evaporation of the water in the plant, which carries with it a certain amount of VOCs. The second one is around 175C, which is due to the vaporization of the major parts of VOCs. The application of a fire retardant increases the emission of VOCs due to the presence of the water (80%) in the fire retardant. However, the use of the retardant results in a lower production of VOCs than using water alone. The measurements are used to estimate the concentration of VOCs potentially produced during the propagation of a specific fire and compared to the flammability limits of a-pinene. It is concluded that the quantities of VOCs emitted by Rosmarinus officinalis shrubs under certain fire conditions are capable of creating an accelerating forest fire