People trapped after disasters could be rescued by searching for the chemicals in their breath, scientists report.
Research published in the Journal of Breath Research describes experiments using volunteers in a mock-up of a collapsed building.
Molecules such as acetone and ammonia in the participants' breath were easily detected through the simulated rubble.
The findings are being used to develop an "electronic sniffer dog" that could search disaster sites for survivors.
A demonstration device has already been produced by one of the collaborators on the research, but the intent is to supplement rather than replace the search-and-rescue dogs currently employed.
"Dogs are fantastic but they don't work for very long, and they undergo injury and suffering as a result of their work in a search and rescue environment," said Paul Thomas, the Loughborough University chemist who led the research.
"We don't know what the dogs detect. The whole Second Generation Locator project is about producing better sensors and systems that can find people," Professor Thomas told BBC News.
Rescue dog in Tohoku earthquake effort Rescue dogs work for short periods, risking life and limb
"We need to try and define in scientific terms what a 'signs of life detector' would need to respond to. But what starts from a human and travels through building may not be what gets to the end of the building - there's a whole range of materials that it has to pass over and through."
To determine what chemicals future detector technology should be sensitive to, Professor Thomas and his colleagues carried out a series of experiments using eight volunteers confined in a box for six hours.
The gases escaping from the box were gathered up and passed through a cylinder filled with building materials simulating more than two metres of rubble from a glass and reinforced concrete building.
A wide array of instruments measured what came through the materials.
The team found a number of molecules that were detectable, principally carbon dioxide and ammonia, along with acetone and isoprene.
Professor Thomas said that the demonstration "signs of life detector" that the team used "worked beautifully".
"Our chemical sensors detected what we were looking for rapidly, within an hour of someone being 'buried' there."
The team will now carry out further tests using longer periods in the simulator; as the volunteers spend longer and longer without food, a different array of "metabolite" chemicals should become apparent, as well as chemical components of urine that trapped victims would likely release
By Jason Palmer Science and technology reporter, BBC News
12 September 2011 Last updated at 13:25
http://www.bbc.co.uk/news/science-environment-14859492
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