Scientists on Sunday said they had devised sensors to detect breath and sweat which one day could locate survivors buried under buildings hit by an earthquake or a bomb blast.

"This is the first scientific study on sensing systems that could detect trapped people," said Paul Thomas, a professor at Loughborough University in central England.

The sensors sniff out metabolites, the gassy by-products of breakdown mechanisms, which come from breathing, sweating and urinating.

Dogs can be trained to detect these compounds, but are expensive to train, need frequent rest periods and both animal and trainer are exposed to danger during search operations.

"A device could be used in the field without laboratory support. It could monitor signs of life for prolonged periods and be deployed in large numbers," said Thomas.

The tests sought to duplicate the conditions of a real disaster, in which eight volunteers spent five six-hour days in the simulation of a collapsed, glass-clad, reinforced-concrete building.

The compounds secreted by the volunteers body interacted with materials in the debris, and changed with conditions such as humidity, heat, and wind strength and direction, making the detection process much more difficult.

The sensors rapidly detected human-generated carbon dioxide and ammonia in plumes of air that wafted through gaps in the "rubble."

The devices also picked up the scent of other volatile organic compounds cast off by human bodies, such as acetone and isoprene.

Intriguingly, there was a marked decrease in ammonia levels when the participants were asleep, but researchers could not explain why.

The study appeared in the Journal of Breath Research, published by Britain's Institute of Physics (IOP).