Sylvain Suard

Fuel Mass-Loss Rate Determination in a Confined and Mechanically Ventilated Compartment Fire Using a Global Approach

Fire development is generally characterized in terms of evolution of heat release with time, and its determination thus represents an essential aspect of a fire hazard analysis. Since it is not a fundamental property of a fuel, heat release cannot be calculated from the basic material properties, and one generally resorts to experiments to determine it. In this article, we present a theoretical formulation that allows the determination of the burning rate of fuels for pool fires in a closed compartment. It is based on an energy balance at the pool fire surface and includes radiative and convective heat components from the flame to the pool surface by relating them to the ambient oxygen mass fraction at the flame base. Fuel response to vitiated air as well as burning enhancement due to hot gases and confinement are taken into account. The formulation was first compared with the empirical correlation determined by Peatross and Beyler before being implemented in a computational fluid dynamics (CFD) code and validated against two experiments involving a hydrogenated tetra-propylene pool fire test enclosed in a confined and mechanically ventilated compartment. These experiments were conducted in conditions for which external heat fluxes were either negligible or significant. It is shown that this approach is able to correctly predict the fuel mass loss rate and provides a reasonable assessment of the heat flux from the flame to the pool surface.

Analytical Approach for Predicting Effects of Vitiated Air on the Mass Loss Rate of Large Pool Fire in Confined Compartments

The aim of this study is to determine the vaporization rate of an under-ventilated pool fire in a closed environment. A theoretical model that allows the burning rate of fuels to be determined for compartment fires under vitiated conditions is presented. The radiative and convective components of the heat flux from the flame to the pool surface are both evaluated and related to the ambient oxygen mass fraction. The model was first compared with the empirical correlation determined by Peatross and Beyler [1] before being applied to pool fires using heptane and PMMA as fuels in a small-scale apparatus. The global model presented here was then implemented in the CFD code ISIS and was validated against experiments involving a hydrogenated tetra-propylene pool fire test in a confined and mechanically ventilated compartment. It is shown that the model is able to correctly predict the fuel mass loss rate and provides a reasonable assessment of the heat flux from the flame to the pool surface.

Fire behavior of halogen-free flame retardant electrical cables with the cone calorimeter

Fires involving electrical cables are one of the main hazards in Nuclear Power Plants (NPPs). Cables are complex assemblies including several polymeric parts (insulation, bedding, sheath) constituting fuel sources. This study provides an in-depth characterization of the fire behavior of two halogen-free flame retardant cables used in NPPs using the cone calorimeter. The influence of two key parameters, namely the external heat flux and the spacing between cables, on the cable fire characteristics is especially investigated. The prominent role of the outer sheath material on the ignition and the burning at early times was highlighted. A parameter of utmost importance called transition heat flux, was identified and depends on the composition and the structure of the cable. Below this heat flux, the decomposition is limited and concerns only the sheath. Above it, fire hazard is greatly enhanced because most often non-flame retarded insulation part contributes to heat release. The influence of spacing appears complex, and depends on the considered fire property.

Sensitivity Analysis of a Fire Field Model in the Case of a Large-Scale Compartment Fire Scenario

The objective of this work is to show how a sensitivity study based on a fractional factorial design can be helpful to quantify the impact of parameter variations on model predictions. These parameters have been carefully chosen due to their high variability in fire modeling and the analysis is conducted by simulating a compartment fire with a CFD model. Through a rigorous approach, it is demonstrated that this fractional design composed of eight simulations gives the same information as a standard full design of 64 runs. Physically, it is found that some turbulence and combustion parameters are significant for most the responses.