Helium-Based Simulation of Smoke Spread due to Fire in Enclosed Spaces

This study is directed at the helium smoke simulator which has been used for simulating smoke spread in aircraft cabins during inflight tests. The smoke from cabin fires is buoyant due to the higher temperatures involved, compared to the surroundings. However, the smoke from commercially available smoke generators is nonbuoyant and an addition of helium is employed to make it buoyant so that the actual circumstance is closely represented. The dependence of buoyancy on the amount of helium and the accuracy of the approximation are important questions that need to be answered. In this technique, helium is added to smoke from a commercially available smoke generator in order to provide the buoyancy in the flow due to the lower density of helium. By introducing this buoyancy component in the smoke, the technique can be used to simulate the flow of smoke and toxic gases in the cabin of an aircraft or in other enclosed spaces without resorting to heated air to approximate these gases. Since buoyancy plays a very important role in the flow and spread of smoke and hot gases, it is important that the simulation include this effect in order to closely represent the actual flow. An experimental investigation was undertaken to explore the possibility of simulating thermally buoyant gases, from a fire, with a helium and air mixture. The experimental flow consisted of a ceiling jet with a corner flow. This same configuration was used in a previous study, in which thermally buoyant flows were used. Thus, a basis for comparison between the two buoyant flows can be established. Parameters such as the volume flow rate of the air and helium, and the initial helium concentration were varied over wide ranges. Vertical temperature profiles from the thermally buoyant case were compared to the helium concentration profiles. In addition, velocity profiles from the two studies were compared and contrasted. From these results, a quantitative description of the buoyant characteristics of the helium and air mixture were obtained.