Comportement au Feu des matériaux solides – Formation des polluants gazeux – CompFeu

The aim of this study is to integrate the expertise of fire safety engineering and environmental impact through the assessment of the combustion products issued from a fire. Legislations, standards and codes will be affected by a better understanding. The specific objective is to study the solid phase degradation of materials under fire conditions as an example of integration of flammability and environmental impact. Within the environment of a fire, materials degrade leading to the production of different species. This study intends to deepen our understanding of material degradation with the objective of achieving fire control (mastering of flammability) while minimizing environmental impact. The investigation concerns the determination of the physical and chemical properties of the thermal degradation of solid materials, and the validation of the kinetic parameters by a comparison of experimental and numerical results Description Through out all stages material degradation has a critical importance, principally to understand the different detailed physical and chemical mechanisms associated to the thermal degradation, to the fire and leading to the formation of the main species identified. Chemical and physical processes occurring within the solid and gas phases will be associated to these observable parameters describing fire behaviour to establish their link with the production of pyrolysis gases, chemical reactions and product composition. This is an ambitious task thus simplified mechanisms will be privileged. The parameters used as variables in the study are those of the different regimes associated to a fire: oxygen concentration, flow velocities, environmental temperatures and externally imposed heat fluxes, depending of the test methods: cone calorimeter, LIFT, tube furnaces with gas measurements. Measurements will be analyzed using FDS. Those experimental results will be used to determine the constant kinetic parameters of the degradation and of the pollutants formation (constants of Arrhenius law). This investigation will be conduct using the genetic algorithm approach. The parameters obtained will be included into the FDS code in order to: - add a realistic chemistry to the pyrolysis model that includes a much broader set of materials. Currently the materials library is very limited in FDS. - improve species production prediction within the combustion model. Generally test methods use a very simplified treatment of the gas phase that leads to analytical solutions. The use of CFD tools in the interpretation of the data opens the door to a clearer definition of the processes involved. The data leads to improved models that will enhance the performance of the tools. The numerous parameters to be varied and measurements made will also allow a detailed validation of the improved CFD tools. The toll chosen is FDS, that because of its treatment of buoyant flows enables tractable transient calculations of fire induced flows (the most common CFD code used in fire safety). The nature of the code does not allow the integration of simple multi step chemistry, thus will require an innovative treatment that gives equivalent results. Global chemical kinetic parameters can lead to the establishment of reduced mechanisms that allow the computations to remain tractable. The FDS code will be used to simulate firstly the fire of products. The results of the simulation will be compared to the experimental results obtained at middle scale. This is a very important step, since it will be useful for the fitting and the validation of the kinetic parameters already determined. In a second time FDS is used to simulate fire scenario: fire in a building and fire in transportation. Results Currently the biggest and most determining errors within CFD calculations are associated to the solid phase and to the following of species. Both processes are of extreme importance if CFD tools are to be used for fire safety engineering applications. This programme has thus the potential of a strong impact on the utilization of these tools. Furthermore, the use of CFD tools and sophisticated diagnostics within standard material flammability testing will enhance the value of these tests. These contributions will have an impact on the 'National Ingénierie de la Sécurité Incendie' where these techniques and methods are yet to be included. It is expected that these results will have an impact on the development of new standards and on the ways in which tools such as CFD codes are used in the practice. The results of the present programme will provide better quantified input parameters associated to the degradation and combustion processes. Finally, this project will provide new practice guidelines in the design of buildings and transport vehicles where the productions of species are included in an integrated manner. This is advancement over current practices where focus is on fire resistance and reaction to fire solely.