Ventilation to Eliminate Oxygen Deficiency in a Confined Space—Part III: Heavier-Than-Air Characteristics

Abstract

This study investigated characteristics of ventilation to eliminate oxygen deficiency caused by heavier-than-air (HTA) contaminants in confined space (CS) models. The HTA “contaminant” gases were carbon dioxide, halocarbon-22, and sulfur hexafluoride, having specific gravities (SG) of approximately 1.5, 3.0, and 5.0, respectively. Neutrally bouyant nitrogen (SG = 0.98) also was tested, consistent with previous studies. CS models having cubical and vertical noncubical shapes were tested. Other variable design parameters included ventilation mode (exhaust and supply), volume flow rate, inlet/outlet elevation, and sampling elevation inside the CS model. Testing confirmed that HTA contaminants would stratify in the CS models. Regressions of experimental data provide a means to calculate oxygen recovery times from initial deficiencies. Ventilation time was found to increase significantly with increasing contaminant SG. The effect was most pronounced at low CS model elevations. Supply ventilation was more effective than was exhaust. A low ventilation inlet/outlet elevation was considerably more effective than was a high elevation. Geometrically similar cubical models of different size performed in very similar manners. Results for vertical, non-cubical CS models emphasized the importance of introducing ventilation near the bottom of the space. Guidelines for CS ventilation from this and previous studies, additional issues, and recommendations are discussed.