Fire development in passive houses: experimental analysis and validation of theoretical models

Abstract

The need for sustainability leads to the construction of more airtight buildings to increase the energy efficiency, according to the Directive 2010/31/EU. New kinds of building like passive houses are thus developing to diminish the environmental impact. So there can be risks related to the pressure increase due to the thermal expansion of fumes in such structures in case of fire. The aim of this report is thus to examine the influence of building airtightness on fire pressure and its consequences about the safety of occupants and firefighters. Before this thesis work, five full-scale experiments were carried out: two in 2016 by Berthelot, three in 2017 by Piret-Gérard. Another experiment was performed by Caravita on 19/12/2017. All experiments were carried out with different fire loads and ventilation to study the behaviour of pressure and heat release rate during a fire. Then they were used during this thesis work to validate two software (CFAST and FDS) to provide tools to architects and engineers for projecting safer edifices. The pressures obtained by the experiments have different orders of magnitude (from 420 Pa to 2035 Pa) depending on the fire load and the ventilation. All experiments highlight some problems of overpressure in very airtight houses like passive houses in case of fire. Through many simulations of the experiments, it was demonstrated that both CFAST and FDS can be used to predict these problems of overpressure. The CFAST simulations of the compartment without mechanical ventilation differ from the experimental curves of 40% at maximum, while those with mechanical ventilation are roughly the same of the experimental ones, only 25% of difference. The difference between the simulated and the experimental curves concerning FDS (with and without ventilation) is at most equal to 25%. So, it can be affirmed thanks to this thesis work that both software can be employed by architects and engineers to study the behaviour of a fire in a passive house