Contaminant reduction by ventilation in a confined space model--toxic concentrations versus oxygen deficiency

Airborne contaminants can create hazardous conditions in confined spaces (CS) across a broad range of concentrations, e.g., from relatively low, potentially toxic levels (ppm) to much higher levels (%) causing oxygen deficiency. This study investigated ventilation characteristics for isobutylene (IBE) at relatively low concentrations, simulating toxic levels. Experimental data were compared to results from previous studies of oxygen deficiency. Data were obtained at several locations in a cubical CS model, with several variable test parameters: ventilation mode (exhaust and supply), volume flow rate ("air changes" per hour), and ventilation inlet/outlet elevation (% of model height). Findings indicated similar ventilation characteristics, in general, for simulated toxic (IBE) levels compared to oxygen deficiency. Both IBE and O2 deficiency data have shown that supply ventilation is typically more effective than exhaust and that CS locations aligned with supply outlets experience much more rapid contaminant reduction than do other locations. The data suggest that highly accurate predictions of ventilation characteristics cannot be expected for all cases with widely different contaminants and concentrations. Findings from this study indicate that ventilation guidelines for one range of contaminant concentration (e.g., causing oxygen deficiency) can be extended reasonably to encompass a broader range of concentration (e.g., to include toxic or flammable atmospheres).