On the effectiveness of shelter-in-place as a measure to reduce harm from atmospheric releases.

Shelter-in-place (SIP) is recommended by numerous entities as a measure to reduce harm in the event of a chemical accident or chemical attack taking place in the atmosphere. This article, based on solving mass conservation equation for indoor hazardous material, examines how effective SIP is to reduce the harm. It is shown that SIP can be effective when the shelter's air exchange rate is low and when the release duration is short. The effectiveness is strongly affected by the hazardous material itself: SIP is more effective for hazardous material with higher toxic load exponent. Another finding is that leaving the shelter promptly after the event can also be critical.