Evacuation decisions in chemical incidents benefit from expert health advice.

entail moving people through a much higher exposure, albeit for a shorter duration. Our results show that direct exposure to smoke is a more important determinant of ill health than the cumulative exposure to smoke. These results are consistent with other studies. 3 7 Reasons for evacuation Despite the expert guidance, an unacceptably high proportion of chemical incidents worldwide result in evacuations. Possible reasons include an instinctive response on the behalf of emergency services to evacuate populations in danger, and the preference to " play it safe " by first responders, 3 and delay in getting appropriate advice. Initial decisions are often taken under very stressful conditions. Lack of experience has also been proposed since greater frequency of evacuations is reported from areas where chemical incidents are uncommon. 11 We thank the participants in this study for taking the time to complete the questionnaires. We also appreciate the help provided by Geoff Chamings and Shaun Carter at Devon County Council, who converted the postcode references into distance between the factory and the residences. Ethical approval: Not required at the time. The study was carried out in 1999, when ethics approval was not considered an issue for such studies conducted by health agencies as part of their responsibility. 1 Purdy G, Davies PC. Toxic gas incidents—some important considerations for emergency planning. In: The assessment and control of major hazards. Rugby: Institute of Chemical Engineers, 1985. 2 NHS Executive. Deliberate release of biological and chemical agents: Guidance to help plan the health service response. London: Department of Health, 2000. 3 Essery G. On site emergency planning and the use of predictive techniques. Acute effects of nitrogen dioxide after accidental release. Kinra et al have evaluated symptoms arising from a fire at a plastics factory that lasted 48 hours, in which partial evacuation of the area took place in the first six hours, with most residents remaining indoors for the rest of the emergency. 1 Statutory emergency planning and advice for people living around designated hazardous installations that manufacture or store chemicals has been based on mathematical modelling of the most likely scenarios for the catastrophic failure of storage vessels or other failures in the plant, in which the duration of flow of a cloud of chemicals that are accidentally released, neutral, or denser than air will be less than 30 minutes (the average time for countermeasures to be implemented). 2 Peak exposure …