Inert gas agents have the potential to be widely used in fire suppression systems due to health and safety concerns associated with active chemicals. To suppress fire while minimizing hypoxic effects in an occupied area, the discharge quantity of inert gas agents should be carefully designed to dilute the oxygen concentration to a specific threshold level. In this study, the general expressions between oxygen concentration, the discharge rate of inert gas agents, and the ventilation rate of the air-agent mixture are derived first. Then, explicit formulas to calculate the discharge/ventilation rate and the required quantity of inert gas agents are given if the discharge rate and ventilation rate both are constants. To investigate the dilution and fire extinguishing efficiencies of inert gas agents, two scenarios with a discharge of inert gas agents into an enclosure are modeled using the Fire Dynamic Simulator (FDS). The simulation results show that the average oxygen mass fraction approximately reaches the design level at the end of the discharge period. Variation in oxygen concentration along the enclosure height is analyzed. For the scenario with a fire source, oxygen mass fraction decreases fast as oxygen is consumed by the combustion process. Thus, the fire is extinguished a little earlier than the end of the discharge period.

Gas-fire-suppression systems are currently applied to some specific buildings in Norway, as sprinkler systems may not provide sufficient protection in some cases. The application of inert-gas-fire-suppression systems for hazard class 6 buildings needs further intensive validation by experimental and numerical study. Due to the presence of cracks and ventilation systems, it becomes doubtful whether inert-gas agents can extinguish a deep-seated fire located in a leaky enclosure. In this study, tests and numerical simulations were both conducted to investigate the extinguishing effectiveness of inert-gas agents for a closet fire in a leaky apartment. The results show that the location of cracks plays a nonnegligible role in determining the oxygen level in the leaky apartment. The tests and simulations demonstrated that the gas-fire-suppression system successfully extinguished the closet fire even if the activation of the gas-fire-suppression system was postponed or the path available for the inert-gas agent to reach the fire source was narrowed. However, the sprinkler system failed to achieve this. The experimental data also demonstrated that the calculation method proposed in our previous work can be used to estimate the oxygen level in a leaky enclosure.

In this article, an enhanced flame spread model is used to simulate a rail car compartment fire test. The model was found to be able to reproduce the following experiential results: the predicted progressive burning locations are consistent with the experimental record; the predicted temperatures and heat fluxes at various locations essentially follow the measured trends; and the predicted onset of flashover is within 9% of the measured time of 180 s. The sensitivity of the predicted time to flashover is assessed using 18 fire scenarios in which the uncertainties in the measured material properties are systematically examined. The time to flashover is found to be most sensitive to changes in seat material properties. For the investigated rail car compartment, the impact of porosity of the overhead luggage rack structure on time to flashover is also examined and found to be significant for small ignition source fires.