During a chemical fire, evacuation may not be best

Evacuation of local residents during a chemical air pollution incident is not necessarily the best way to prevent exposure to toxic fumes, according to UK investigators.

“Unplanned evacuations where a lot of folks are moved around have the potential for both psychological and physical problems,” Dr. Sanjay Kinra, from the University of Bristol, told Reuters Health.

Following a fire in a plastics factory in southwest England, the initial response of the emergency services was to evacuate residents, but then the decision was changed to recommend that residents remain in their homes. Kinra and his associates analyzed health outcomes among people who stayed and those who left the area.

Testing carried out 12 hours after the fire began showed a maximum concentration of hydrochloric acid of 5 parts per million, according to the report in this week’s British Medical Journal.

Kinra’s group included in their analysis subjects living within 1000 meters of the fire. On average, respiratory symptom scores were higher in the 299 evacuees than the 797 people who remained sheltered during the incident, the team found.

Nearly 20 percent of the evacuees had severe symptoms compared with 10 percent of the ones who stayed. The two individuals who were hospitalized - one for bronchial asthma and one for suspected angina - were both evacuees.

A population can be protected from exposure during chemical incidents either by placing a barrier between residents and the gas or by creating a distance between them and the gas, Kinra noted.

But “to create that distance, in most cases you have to go through it,” he said. On the other hand, “If you remain in a house, you can reduce exposure by 30 to 50 times just by shutting doors and window and putting blankets or towels under the doors and windows.”

His group’s findings support expert opinion on the subject, he added. The problem was that the guidance was based on computer analysis. Therefore, “it was hard to push because it was not based on the real thing and people are not convinced.”

In a related editorial, Dr. Peter J. Baxter, from the University of Cambridge, points out that plumes from burning chemical warehouses tend to present little immediate risk - because of buoyancy provided by heat of the fire - but in situations such as the crash of a tanker containing toxic gas, temporary evacuation may be required.

“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,” Baxter comments.

SOURCE: British Medical Journal, June 25, 2005.

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