Fire Safety Science Digital Archive

Small scale tests were made to study the replacement of the atmosphere in a compartment by an inert gas. The condition necessary for the replacement of the atmosphere in a compartment with another atmosphere of different density by stratified flow is the introduction of the replacing atmosphere over a large area at a low velocity. This can be done by introducing the replacing atmosphere through a filter bag. A lighter replacing atmosphere must be introduced at high level, and the compartment must be vented at low level for efficient replacement. A modified Richardson number greater than 2 is necessary to attain a high degree of stratified flow. For many practical situations the introduction of the replacing atmosphere by turbulent mixing flow appears more satisfactory than by plug flow.