In the event of a short-term, large-scale toxic chemical release to the atmosphere, shelterin-place (SIP) may be used as an emergency response to protect public health. We modeled hypothetical releases using realistic, empirical parameters to explore how key factors influence SIP effectiveness for single-family dwellings in a residential district. Four classes of factors were evaluated in this case-study: (a) time scales associated with release duration, SIP implementation delay, and SIP termination; (b) building air-exchange rates, including air infiltration and ventilation; (c) the degree of sorption of toxic chemicals to indoor surfaces; and (d) the shape of the dose-response relationship for acute adverse health effects. Houses with lower air leakage are more effective shelters, and thus variability in the air leakage of dwellings is associated with varying degrees of SIP protection in a community. Sorption on indoor surfaces improves SIP effectiveness by lowering the peak indoor concentrations and reducing the amount of contamination in the indoor air. Nonlinear dose-response relationships imply substantial reduction in adverse health effects from lowering the peak exposure concentration. However, if the scenario is unfavorable for sheltering (e.g. sheltering in leaky houses for protection against a nonsorbing chemical with a linear dose-response), the community must implement SIP without delay and exit from shelter when it first becomes safe to do so. Otherwise, the community can be subjected to even greater risk than if they did not take shelter indoors.Keywords: sorption, infiltration, air-exchange rate, toxic chemical, emergency response. * Corresponding author. Tel: +1-510-486-6591; fax: +1-510-486-6658.Email address: ajgadgil@lbl.gov (A.J. Gadgil).
2/31Submitted to Atmospheric Environment November 21, 2006
IntroductionIn the event of a sudden, large-scale release of a toxic chemical into the atmosphere, nearby populations may be advised to take shelter indoors. Shelter-in-place (SIP) requires simply being indoors, closing doors and windows, and turning off fans. Broadly, SIP offers protection through two modes. First, lower peak indoor concentrations compared to outdoor concentrations are encountered after a short-term release because building envelopes limit indoor-outdoor air exchange. Second, sheltering may reduce cumulative exposures through one or more mechanisms, including transformations of toxic chemicals on building surfaces and timedependent manipulation of ventilation rates.The effectiveness of SIP for protecting public health can depend upon many factors.Attributes of the release, such as the quantity emitted, toxicity of the chemical, release duration, and atmospheric transport and dispersion, influence the effectiveness of protection. Building characteristics, including leakiness of the building envelope and the interactions between the toxic chemicals and building surfaces, also play an important role. Finally, human factors such as delays in notification and response, and the t...