Characterisation of smoke from controlled wildland fires : source terms, emission phases and impact on operational staff

Ce travail de thèse s’inscrit dans le contexte de la protection contre les risques incendies de végétation. L’objectif principal est la caractérisation des fumées et la définition de termes sources et de critères d’inflammation utilisables en modélisation, à des fins d’améliorations des outils d’aides à la décision pour la gestion des risques incendies. Le second objectif est l’observation de l’impact de l’exposition aux fumées sur la santé humaine.La réaction au feu de deux combustibles végétaux, Cistus monspeliensis et Pteridium aquilinum, a été étudiée en laboratoire à l’échelle du cône calorimètre et du LSHR (Large Scale Heat Release). L’étude des propriétés d’inflammation et de la dynamique de combustion des végétaux a montré l’influence de leur épaisseur et de leur structure sur le temps et la température d’ignition ainsi que sur l’énergie libérée. Elle a permis de définir une taille limite des particules végétales relative à un changement de comportement au feu ainsi qu’un critère d’inflammation indépendant de l’épaisseur et de la structure du combustible.La caractérisation des fumées a été réalisée en laboratoire (cône calorimètre et LSHR) et sur le terrain (brûlages dirigés). Elle a mis en exergue l’importance de la phase de combustion pour la composition des émissions, notamment pour les aérosols. D’importantes quantités de goudrons sont émises durant la phase de pré-ignition tandis que les suies sont émises lors de la phase de flamme. Elle a notamment permis le calcul de facteurs d’émission des effluents propres à la végétation méditerranéenne, utilisables dans les modèles de simulation couplés feu/atmosphère. Cette étude a également souligné l’effet d’échelle sur la production et la composition des fumées.Sur les feux de terrain, cette caractérisation a été effectuée à deux niveaux (dans le panache de fumées et dans l’atmosphère de travail des opérationnels). L’analyse de l’atmosphère de travail des opérationnels en conditions de brûlages dirigés et le suivi de biomarqueurs d’exposition aux fumées ont révélés une surexposition à des composés toxiques (irritants, asphyxiants et CMR : cancérogènes, mutagènes et reprotoxiques) susceptible d’induire des effets sur la santé. Des recommandations sur les pratiques de brûlages dirigés (période, horaires, conditions atmosphériques, positionnement) ont alors été apportées dans ce travail, en vue de réduire l’exposition aux fumées.This thesis fits in the context of the protection against wildfire risks. The main goal is the characterization of smoke and the definition of source terms and ignition criterions, available for modelization, to improve decision support tools for fire risk management. The second objective deals with the impact of smoke exposure on human health.Flammability of vegetation fuel was studied at laboratory scale using two calorimeters (cone and Large Scale Heat Release), for two species: Cistus monspeliensis and Pteridium aquilinum. The study of ignition properties and combustion dynamics of plants showed the influence of their thickness and structure on ignition time, ignition temperature and on heat release. A limit size of fuel particles for burning behavior was defined as well as an ignition criterion independent of fuel thickness and structure.Characterization of smoke was carried out at laboratory scale (cone and LSHR) and ground scale (prescribed burns). It highlights the importance of combustion phases for smoke composition, especially for aerosols. Large quantities of tars are released during the pre-ignition phase while soot are released in flaming phase. Emission factors of effluents characteristic of Mediterranean vegetation were obtained, that can be used in fire/atmosphere modelling. This study also emphasizes the scale effect on smoke production and composition.During ground fires, the characterization was conducted at two locations (in the smoke plume and in firefighters working atmosphere). The analysis of firefighters working atmosphere in prescribed burning conditions and the following of smoke exposure biomarkers (in exhaled breath and urines) showed an overexposure to toxic compounds (irritating, asphyxiating and CMR: carcinogenic, mutagenic and reprotoxic). Recommendations on prescribed burning practices (period, timetable, atmospheric conditions, positioning) were provided in order to attempt reducing the smoke exposure

Caractérisation des fumées issues de feux de végétation contrôlés : termes sources, phases d’émission et impact sur les opérationnels

This thesis fits in the context of the protection against wildfire risks. The main goal is the characterization of smoke and the definition of source terms and ignition criterions, available for modelization, to improve decision support tools for fire risk management. The second objective deals with the impact of smoke exposure on human health.Flammability of vegetation fuel was studied at laboratory scale using two calorimeters (cone and Large Scale Heat Release), for two species: Cistus monspeliensis and Pteridium aquilinum. The study of ignition properties and combustion dynamics of plants showed the influence of their thickness and structure on ignition time, ignition temperature and on heat release. A limit size of fuel particles for burning behavior was defined as well as an ignition criterion independent of fuel thickness and structure.Characterization of smoke was carried out at laboratory scale (cone and LSHR) and ground scale (prescribed burns). It highlights the importance of combustion phases for smoke composition, especially for aerosols. Large quantities of tars are released during the pre-ignition phase while soot are released in flaming phase. Emission factors of effluents characteristic of Mediterranean vegetation were obtained, that can be used in fire/atmosphere modelling. This study also emphasizes the scale effect on smoke production and composition.During ground fires, the characterization was conducted at two locations (in the smoke plume and in firefighters working atmosphere). The analysis of firefighters working atmosphere in prescribed burning conditions and the following of smoke exposure biomarkers (in exhaled breath and urines) showed an overexposure to toxic compounds (irritating, asphyxiating and CMR: carcinogenic, mutagenic and reprotoxic). Recommendations on prescribed burning practices (period, timetable, atmospheric conditions, positioning) were provided in order to attempt reducing the smoke exposure.Ce travail de thèse s’inscrit dans le contexte de la protection contre les risques incendies de végétation. L’objectif principal est la caractérisation des fumées et la définition de termes sources et de critères d’inflammation utilisables en modélisation, à des fins d’améliorations des outils d’aides à la décision pour la gestion des risques incendies. Le second objectif est l’observation de l’impact de l’exposition aux fumées sur la santé humaine.La réaction au feu de deux combustibles végétaux, Cistus monspeliensis et Pteridium aquilinum, a été étudiée en laboratoire à l’échelle du cône calorimètre et du LSHR (Large Scale Heat Release). L’étude des propriétés d’inflammation et de la dynamique de combustion des végétaux a montré l’influence de leur épaisseur et de leur structure sur le temps et la température d’ignition ainsi que sur l’énergie libérée. Elle a permis de définir une taille limite des particules végétales relative à un changement de comportement au feu ainsi qu’un critère d’inflammation indépendant de l’épaisseur et de la structure du combustible.La caractérisation des fumées a été réalisée en laboratoire (cône calorimètre et LSHR) et sur le terrain (brûlages dirigés). Elle a mis en exergue l’importance de la phase de combustion pour la composition des émissions, notamment pour les aérosols. D’importantes quantités de goudrons sont émises durant la phase de pré-ignition tandis que les suies sont émises lors de la phase de flamme. Elle a notamment permis le calcul de facteurs d’émission des effluents propres à la végétation méditerranéenne, utilisables dans les modèles de simulation couplés feu/atmosphère. Cette étude a également souligné l’effet d’échelle sur la production et la composition des fumées.Sur les feux de terrain, cette caractérisation a été effectuée à deux niveaux (dans le panache de fumées et dans l’atmosphère de travail des opérationnels). L’analyse de l’atmosphère de travail des opérationnels en conditions de brûlages dirigés et le suivi de biomarqueurs d’exposition aux fumées ont révélés une surexposition à des composés toxiques (irritants, asphyxiants et CMR : cancérogènes, mutagènes et reprotoxiques) susceptible d’induire des effets sur la santé. Des recommandations sur les pratiques de brûlages dirigés (période, horaires, conditions atmosphériques, positionnement) ont alors été apportées dans ce travail, en vue de réduire l’exposition aux fumées

Characterization of aerosols emissions from the combustion of dead shrub twigs and leaves using a cone calorimeter

International audienc

Flammability of dead shrub twigs

Communication oral

Mise en évidence de l’influence de l’épaisseur caractéristique des végétaux sur l’autoinflammation de combustibles méditerranéens morts

International audienc

Smoke analysis from forest fuel and effects of toxicity on the organism of the personnel involved

International audienc

Measures of the pollutants emitted during the combustion of Cistus monspeliensis twigs according to the diameters of these particles

International audienceOur study aims to determine the particles size of plant involved in fire spread , in order to estimate the amount of leaves, twigs and wood implicated in fire spread. Thereby, it was determined from thermal parameters (HRR, mass loss, THR, efficiency) that the diameters of Cistus monspeliensis less than 4 mm, burn very quickly. These diameters are considered as elements that contribute to firespread. This first result on the particle size (< 4mm) involved in fire spread will lead to better estimate the fuel load to be taken into account in the propagation models (percentage of real burden of vegetation on the ground according to the effective size of the particles and their fraction in the plant). This fuel load is an important parameter for determining the fire propagation, the calculation of its intensity and the interpretation of its impact. Moreover, it is observed two humps of HRR from particle size above 5 mm. The second humpis increasingly important according to the growth of particles diameters. This result indicates a change in fire behavior of twigs between 4 and 5 mm. These elements largely burn behind the flame front. The second part of this study is devoted to the characterization of pollutants emitted by Cistus monspeliensis twigs burned according to their sizes. It aims to determine the quantities of pollutants potentially inhalable by the personnel involved (firefighters) and the exposed population. Further, it has been shown that CO2 is the most emitted gas with constant quantities according to the particles sizes. Other identified gases are CH4, NOx and 17 NMVOC

Influence of particle size on the heat release rate and smoke opacity during the burning of dead Cistus leaves and twigs

International audienc

Characterization of aerosols emissions from the combustion of dead shrub twigs and leaves using a cone calorimeter

WOS:000407982400091International audienceThis work is a contribution to the understanding of wildfire smoke emissions. It focuses on the characterization of aerosols emitted by the combustion of dead shrub leaves and twigs with different thickness (range of 0.75-20 mm). The experiments were carried out at bench scale with a cone calorimeter for the burning of Cistus monspeliensis leaves and twigs. Auto-igthtion of the samples was obtained by heating their surface with a radiant heat flux of 50 kW/m(2). The smoke and aerosols emitted before ignition during pre-heating were analysed separately from the smoke and aerosols emitted during the flaming phase. Heat release rate (HRR) was also measured and we observed two different behaviours depending on the diameter of the twigs. Fuel samples with diameter smaller than 4 mm exhibit a single peak HRR whereas two peaks were observed for the twigs with larger diameters. The smoke production rate (SPR) was also measured and it showed that smoke was mainly emitted during the pre-heating phase. We also obtained a strong correlation between HRR and SPR during the flaming phase but no smoke was emitted, during the glowing phase. Emission factors of aerosols were calculated depending on these combustion phases (pre-ignition and flaming) and for the range of thickness of the samples. The observations of the aerosols were performed by scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The chemical composition of organic carbon (OC) aerosols, emitted during the pre-ignition phase, were analysed using gas chromatography (GC) coupled with mass spectrometry (MS). Some carcinogenic compounds were identified. The sizes of OC and black carbon (BC) aerosols emitted were measured with an optical device. Most of the BC were PM0.3, which corresponds to the alveolar fraction of particles

Understanding the Relationships between Extensive Livestock Systems, Land-Cover Changes, and CAP Support in Less-Favored Mediterranean Areas

International audienceFarm abandonment and over-extensification trends in less-favored livestock breeding areas in the Mediterranean have led to socio-environmental issues that are difficult to assess and address, due to the characteristics of these areas (e.g., poor data availability and reliability). In a study case that presents many of the characteristics common to these areas, we combine qualitative and quantitative approaches to assess (i) the relationship between livestock production and land-cover change and (ii) the drivers of farmer decisions, concerning the types of livestock they breed. We show that the Common Agricultural Policy's objective of open-landscape preservation cannot be achieved through the observed livestock management practices, with the most heavily CAP subsidy-dependent activities (e.g., suckler-cow breeding) having one of the weakest contributions to this objective. We also econometrically show that suckler-cow breeding is more likely to be adopted as a complementary or main activity in farms facing a labor scarcity and land abundance context. These results complement the literature and contribute to the discussion regarding the design of CAP support for less-favored Mediterranean areas