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Evacuation decisions in chemical incidents benefit from expert health advice

BMJ 2005; 330 doi: https://doi.org/10.1136/bmj.330.7506.1474 (Published 23 June 2005) Cite this as: BMJ 2005;330:1474
  1. Peter J Baxter, consultant occupational physician (Pjb21{at}medschl.cam.ac.uk)1
  1. 1 Department of Public Health and Primary Care, University of Cambridge, Institute of Public Health, Cambridge CB2 2SR

    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 counter-measures to be implemented).2 Peak exposure to an individual living or working nearby at the time when such a chemical cloud disperses should be higher outdoors than inside a building with its doors and windows closed, at least for this short period of time. The difference will depend on how well the building has been sealed against the weather, to reduce normal air infiltration rates. Once the danger has passed, the emergency services would tell people to go outside into the fresh air. Attempts at rapid escape or evacuation are considered to be more dangerous than taking shelter indoors in such short term emergencies, but the adverse health consequences that may follow from this strategy—particularly the effects of exposure to low, cumulative levels of irritant gases in people with asthma and chronic lung disease who do take shelter—need to be studied whenever these unusual incidents occur.

    This “stay indoors” strategy may not necessarily apply to certain chemical incidents of longer duration. Smoke from plastics fires usually contains a mixture of highly irritant substances, together with combustion gases, which for polyvinyl chloride (PVC) is mostly hydrogen chloride (HCl). Kinra et al measured 1 part per million of hydrogen chloride in the ambient air of the residential area on their first testing at 12 hours, and thereafter hydrogen chloride and other gases were undetectable. This very soluble gas is unlikely to produce any reactions in people with asthma at this concentration, and healthy individuals can be exposed to higher levels for prolonged periods without ill effects.3 Other irritants in the smoke will have an additive effect. Acute incidents involving the inhalation of irritant gases (which are among the most important materials stored at major hazard installations and commonly emitted in fires) may, in severe cases, cause toxic pneumonitis and even death, and brief exposure may trigger reactive airways dysfunction syndrome (RADS; irritant induced asthma).3 Kinra et al showed that the adverse respiratory consequences in people with asthma and others were few and concluded that remaining indoors was a safe option in the fire they reported.1

    Temporary evacuation may nevertheless be advisable where a toxic release is threatened, such as in a crash involving a road or rail tanker containing toxic gas. Plumes from burning chemical warehouses, tyre dumps, or plastic stores are usually buoyant from the heat of the fire and may present little immediate risk, but whether they descend to ground level long enough to cause a hazard to the people indoors, and the range at which people could be affected, will depend on the management of the fire by the fire services, the type of materials involved, the wind and weather forecasts, and local topography.4 In warehouse fires, chemical fallout from the plume may contaminate nearby gardens and buildings.5 As these chemical fires can last for hours, or even days, temporary evacuation when conditions permit should always be considered, ideally with advice provided to the emergency services by a public health response team.4 More epidemiological studies with good information on exposure will be essential to build the evidence base for decision making in chemical releases and for management after the incident.

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