Computing Toxic Load for Shelter-in-Place Analysis Using Joint Urban 2003

Abstract

Toxic load is a metric used to quantify acute effects from inhalation exposures. The toxic load to individuals depends on the fluctuations of chemical concentrations because the exposureresponse relationship is often nonlinear. To study the effects of concentration fluctuations on toxic load, we analyzed concentration data from the Joint Urban 2003 series of city-scale tracer gas studies. We summarized the outdoor concentrations measured by fast-response gas analyzers and computed outdoor toxic load. We then analyzed the amount of tracer gas that entered a 16-story office building and compared indoor and outdoor toxic loads. We show that the time aggregation used to compute toxic load is a source of uncertainty in hazard assessments.However, in comparison to other uncertainties and variability inherent in hazard assessments involving buildings, the choice of time averaging interval plays a minor role, especially when toxic load is used to compute other aggregated metrics such as the effectiveness of sheltering indoors. In the absence of compound-specific information to dictate a time average, we propose following Acute Exposure Guideline Levels (AEGLs) and using timescales on the order of minutes for computing indoor toxic load.