A comparative analysis of mathematical models for relating indoor and outdoor toxic gas concentrations in accidental releases

Abstract

This paper surveys various models for estimating indoor concentration as a function of outdoor concentration in the event of an accidental release or chemical attack involving toxic substances. It is essential to know indoor concentration in order to estimate the effectiveness of shelter in place as a protective measure. Several models—deposition, one-sink, sink-diffusion and two-sink—were considered. These models can be derived from a general model by making different assumptions. The models showed significant variations in terms of the adsorption/desorption considerations. Since indoor materials act as reservoirs, adsorption may lead to a significant decrease in indoor concentration, but subsequent desorption may also take place. The models require the knowledge of a set of parameters that are specific to each compound and material, which are currently scarce in the literature. As a result, the more complex and complete the model, the more limited its applicability.

Outdoor concentrations obtained from a Gaussian model and originating from three source types (continuous, temporary and instantaneous) were used as inputs in the reviewed models. Indoor concentrations of chlorine and sarin from a temporary source were estimated in order to compare the predictions of the models.