A chemical incident at a plastics factory has put to the test official UK guidance on how to deal with nearby residents. A partial evacuation during a fire lasting 48 hours in a plastics factory adjoining a large residential area in southwest England afforded researchers the chance to compare for the first time health outcomes between evacuees in the first six hours and residents sheltering at home during the emergency.

In this incident the results of the cross sectional study upheld the guidance, which is for residents to shelter at home. Health outcomes were better for those who stayed indoors: they had significantly fewer mean symptom scores, though the difference lessened with time. The main risk factors contributing to becoming a case (having ⩾4 symptoms) were evacuation (odds ratio (OR) 2.5) and direct exposure to smoke for more than two hours at the time (OR 2.0).

Health outcomes were assessed by a postal questionnaire based on existing models in London and Wales, which was sent to all residents in the vicinity—472 evacuees and 1278 who remained indoors. Response rate was 63% overall: 27% (299) for evacuees and 73% (797) for sheltering residents.

Official guidance relies on mathematical models of likely scenarios after incidents at storage sites or in the plant releasing a chemical cloud for 30 minutes, but the consequences of exposure to low cumulative amounts of irritant gases in people with health compromised by, for example, asthma and chronic lung disease need to be studied.

However, staying indoors may not be best if toxic irritant gases are inhaled in large amounts over longer time, contends one public health expert. Toxic pneumonitis and even death can result, and even short exposure may trigger airways dysfunction syndrome. In the incident described, complications of asthma and other respiratory diseases were few, and environmental sampling 12 hours after the fire started detected only 1 ppm hydrogen chloride 100 m downwind within the smoke plume; other irritant gases were undetectable.

Temporary evacuation may be called for depending on management of the fire, materials involved, wind and weather forecasts, and local topography. It should always be considered, ideally with advice from the public health response team, in chemical fires, which can last for days. More epidemiological studies and good information on exposure are essential to test the validity of the guidance in such circumstances