As part of a series investigating the elimination of oxygen deficiency in confined spaces, heavier than air (HTA) contaminants were considered. A HTA contaminant was used to displace oxygen in a confined space model. Oxygen concentrations were measured at different locations inside the model both prior to and following mechanical ventilation of the model with fresh air. Contaminants included carbon-dioxide (124389) (CO), halocarbon-22 (HC-22), and sulfur-hexafluoride (2551624) (SF6). The results demonstrated that air movement caused by mechanical ventilation will greatly enhance contaminant dilution inside a confined space. Heavier than air contaminants could stratify inside the confined spaces. Supply ventilation was generally more effective than exhaust ventilation in reducing the length of time required for dilution of atmospheric contaminants because air mixing was enhanced by the supply jet. A directed supply jet of fresh air provided very effective air mixing and dilution at locations aligned with the jet. Low ventilation inlet/outlet (I/O) elevations were generally more effective than higher I/O elevations. Ventilation volume flow rate had significant effects upon ventilation time. If geometric and air flow similarity were maintained between two confined spaces of different size, then they would probably have similar ventilation characteristics. The shape of the confined space could have significant effects on ventilation characteristics. Variations in ventilation effects with shape were less pronounced when contaminant density was not significantly different from air.
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