Sampling and quantitative analysis of Volatile Organic Compounds implicated in the phenomenon of flash-over.
Résumé
Certain Mediterranean plants (e.g. Rosmarinus officinalis, Cistus albidus, Pinus halepensis) produce and emit volatile substances related to their secondary metabolism, [1,2]. The composition of these substances is flammable. The assumption is that these emitted compounds are found in concentrations close to the Lower Flammability Limit (LFL) at periods when the plants are themselves highly flammable. To obtain this critical situation, it is necessary that these chemical products can accumulate in certain geographical zones (e.g. small valleys, thalweg). The conjugation of these two effects (accumulation and flammability) is capable of causing situations with high potential of ignition, and consequently a strong risk for the fire-fighters. There exist few studies on the implication of the Volatile Organic Compounds (VOC) in the phenomenon of blow-up in wildland fires, [3,4], contrary to their impact as precursor of ozone, [5,6]. In France, over the last 15 years one counts eleven cases of blow-up in wildland fires involved the death of thirteen fire-fighters, [7]. Similar accidents occurred in Portugal, [8,9], and in the United States, [10]. The aim of the present work is to characterise the emission of the VOC responsible for the phenomenon of blow-up in wildland fires on a representative vegetation of the Mediterranean basin such as Rosmarinus officinalis. In this study we simulate the fire intensity by a radiant panel in order to measure the impact of thermal radiation and to evaluate the effect of the fire retardant on the VOC emissions. For that, an original experimental protocol which consists in placing a plant in a hermetic enclosure and to heat it by a radiant panel has been developed, cf. Figure 1. The qualitative and quantitative analysis of the VOC is carried out with an Automatic Thermal Desorber coupled with a Gas Chromatograph-Mass Spectrometer (ATD-GC-MS).