Stay indoors or evacuate to avoid exposure to toxic gas?

Evacuation of people from their homes and workplaces is a standard response to the hazards created by the release of toxic gas. However, by staying indoors a person can take advantage of the clean air stored within the house volume, as well as the damping the house provides for sudden changes in outdoor toxic gas concentration. The relation between indoor and outdoor concentration is explored in this study, where it is shown that in most cases the risk of exposure to high concentration levels is substantially reduced by remaining indoors during the entire period of toxic gas release. Ratios of indoor to outdoor concentration are presented for typical rates of air infiltration and outdoor concentration variation.