Building Ventilation Strategies to Protect Public Health during Chemical Emergencies

Releases of airborne chemicals can rapidly affect wide areas, leading to exposures that may adversely affect public health. A strategy of sheltering indoors has often successfully protected public health, but in some cases it has been ineffective. This paper explores the role of ventilation as one of a number of factors that affect shelter effectiveness. Ventilation directly influences indoor exposure during chemical emergencies, and theoretical incident and ventilation scenarios are used to show how air exchange rates and chemical dose-response characteristics determine indoor dose and effects on health. For chemicals for which the likelihood of adverse health effects is driven by exposure concentration (peak exposure), sheltering in place for short periods can be an effective protective measure, because the dilution of outdoor air mixing with indoor air reduces the maximum concentration indoors. It is important to minimise ventilation before an outdoor hazard arrives. Delays in maximising ventilation after it has passed are less likely to cause extra harm, since most protection has already resulted from the lower peak exposure concentration indoors during the hazard's passage outdoors. For chemicals for which the likelihood of adverse health effects is driven by both time and concentration (cumulative exposure), which include those that exhibit a linear dose-response relationship, it is particularly important for people to both promptly minimise ventilation before an outdoor hazard arrives and maximise ventilation after it has passed, in order to minimise their cumulative exposure. Most UK residential properties are naturally ventilated, but there is an increasing trend towards the use of mechanical ventilation in new-build properties that are more airtight than their predecessors. The installation, maintenance and use of such systems pose a number of considerations. The potential for ventilation filters to offer additional protection is worthy of further attention.