Evacuation by the emergency services during a chemical incident is not necessarily the best approach for health, according to a study at Bristol University.
Sheltering at home may be more appropriate than evacuation for protecting the health of local residents close to chemical air pollution incidents, says a paper published in this week's British Medical Journal.
In the first study of its kind, researchers compared the effects of both sheltering and evacuation on the local population during a fire at a plastics factory in Devon, which resulted in hazardous chemicals being released into the surrounding environment.
During the first six hours, many of the local residents were evacuated. But it was then decided that remaining residents should stay in their homes. Researchers looked at the number of 'cases' in both groups - i.e. those experiencing symptoms related to the incident.
They found that soon after the fire, the evacuated group had almost twice as many cases as compared with those in the sheltered group (19.7 per cent compared to 9.5 per cent). Though the difference did not seem to persist after two weeks (3.3 per cent compared to 1.9 per cent).
The study was based on a health survey involving 1,096 residents in the town of Paignton - 797 of whom were sheltered and 299 evacuated. Both evacuated and sheltered sets of residents lived similar average distances from the factory (around 500 metres).
The effects of severe chemical air pollution are similar to those of respiratory illness, say the authors - cough, for instance, or runny eyes. To distinguish cases - those whose symptoms were incident-related - they compared how many of these symptoms were typically suffered by a neighbouring community, unaffected by the fire, with those in the affected town. With an average of 0.48 symptoms per person in the nearby town, the researchers defined a case in the affected town as someone with at least four symptoms.
The authors stress that there were several limitations with this study, including a lack of data on whether the level and nature of the smoke exposure could have been different between the groups.
Sheltering may have been a better protective action than evacuation in this chemical incident, they conclude, which confirmed expert advice recommending sheltering in serious chemical air pollution incidents.
Dr Sanjay Kinra, lecturer in epidemiology and public health medicine in the university's Department of Social Medicine, said: "Sheltering is increasingly being seen as the preferred option in most, or many circumstances and this study provides the first evidence to back up that policy.
"It will be valuable to both public health officials and the emergency services in policy setting."