Flame extinction and burning behaviour of timber under varied oxygen concentrations

Self-extinction plays a crucial role in enabling the safe use of timber structures in mid- and high-rise construction, where structural integrity during and after a fire is critical. To date, the influence that oxygen concentration may have in the conditions that lead to self-extinction has not been studied in depth. Also, the thermal conditions of timber after self-extinction has occurred have not been carefully studied. During fires, oxygen concentrations will defer from those during ambient conditions. Within this study, the testing conditions were carefully controlled to investigate the circumstances before and after the occurrence of self-extinction; considering a range of heat exposures and oxygen concentrations in the air surrounding the test sample. For samples tested in air containing 21% oxygen, self-extinction always occurs for an incident heat flux of 30 kW/m but never occurs for 40 kW/m; with the critical mass loss rate that leads to self-extinction being 3.6 ± 0.4 g/ms. The study concluded that lower oxygen concentrations result in an increase of the critical mass loss rate leading to self-extinction and an increase of the minimum incident heat flux leading self-extinction.