Reprinted with permission from CSIRO's "Onwood" Publication 16 - Autumn 1997
A study of fire crews using rakes, chainsaws nd other hand tools to construct firelines to control bushfires has highlighted the importance of light clothing in reducing the risk of dangerous overheating.
In a collaborative project involving CSIRO, the Commonwealth Institute of Health and Australia's forestry and bushfire control agencies, biomedical scientists measured the stresses firefighters experienced in suppressing well-developed experimentally lit fires in dry eucalypt forest in summer. They also assessed physiological and subjective responses to the stresses. Other members of the study team measured the productivity of the crews.
According to Phil Cheney of the Division, the study, conducted over three summers in Victoria and Western Australia, has provided a factual basis for current work by the International Standards Organisation on drafting a standard for "wildland" firefighter clothing.
A key finding was that the exertions of firefighting make a much bigger contribution than radiation from the fire to increases in body temperature. It follows, Cheney says, that firefighters should wear light, well-ventilated clothing that allows maximum release of metabolic heat - for example, coveralls made of medium density cotton.
"There has been a tendency lately to go to urban firefighter-style heavy gear to protect fire crews from radiation", Cheney says. "This is counterproductive from a physiological point of view - and from a psychological point of view, because it gives them the impression that they can work closer to the fire."
He says if firefighters' clothing prevents heat escaping from the skin, rapid increases in deep body temperature can occur, leading to heat stroke. Cheney advises firefighters to roll up their sleeves so that bare skin is exposed and they can feel if they are too close to the fire.
"You can't work on a fireline and also be clothed to protect yourself from entrapment by the fire", he adds. "Entrapment must be avoided by work practice; there should not be even the remotest thought that your clothing can assist in protecting you."
The study was conducted as part of Project Aquarius, led by Cheney, aimed at assessing the costs and benefits of using aerial water tankers for fire control in Australia. The research with workers on firelines was a component of a broader program to define the most intense bushfires that can be suppressed by hand tools, by bulldozers and by air tankers.
The team found that self-pacing by members of a fireline crew generally resulted in them working at a steady rate of about 45% of their maximum aerobic capacity. "That is pretty stressful; it means that heartbeats are commonly around 150 beats per minute" Cheney says.
Their body temperature rose by about a degree, with metabolic heat accounting for about three-quarters of the increase.
Water loss through sweating averaged more than a litre an hour. Although water was provided and the firefighters were encouraged to drink, most experienced significant dehydration. "Water supply to firefighters is a real problem", Cheney says. "Dehydration is probably a major contributor to fatigue at an earlier stage than one might expect."
"Onwood" is published by CSIRO Forestry and Forest
Editor: Mick Crowe
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Last updated 4 November 2014