Sheltering from an outdoor contaminant plume in a commercial building

In urban areas, inhabitants are typically advised to shelter within buildings in the event of a catastrophic outdoor release of a toxic contaminant. The exposure reduction achieved during sheltering is affected by both the plume and building characteristics. During July 2003, experiments (Joint Urban 2003) were performed in which an outdoor plume of inert tracer gas was produced in an urban setting. For the indoor component of the study, tracer measurements were performed both indoors and outdoors (at the building shell and selected air intakes), at four buildings within the downtown area. Samples were collected using 15-bag programmable samplers, 30-minute integrated samplers, grab samples and gas chromatographs (GC) located within two of the buildings. These measurements were used to assess the effectiveness of sheltering under varying building operating parameters. The effectiveness of sheltering was found to be dependent on both building operation modes and outdoor plume characteristics. In addition, the presumed shape of the toxic load curve (linear, 2nd power, or 4th power, in our examples) had a significant impact on the amount of protection provided by sheltering. This indicates that sheltering is more effective for certain types of toxins. Significant exposure reductions (greater than 95%) were achieved through ventilation system manipulation and optimization of sheltering times. The results illustrate the importance of improving our understanding of indoor and outdoor concentrations to predict concentrations and provide information on optimum sheltering durations for reducing exposures in emergency situations.