Portable sensors can soon be used to identify humans trapped in real-life situation such as under collapsed buildings due to disasters. A study published in the Journal of Breath Research explains how flumes of air can be used to create a profile of molecules indicating the presence of humans in a disaster zone. A team of researchers from the National Technical University of Athens, Loughborough University, University of Dormund and University of Babe-Bolyai conducted "The trapped human experiment" in which they designed and constructed a simulated glass-clad-concrete building. It was tested over a period of five days during which eight participants were asked to enter in at intervals of six hours. Throughout the simulator, various sensors detected ammonia and carbon dioxide present in the plumes of air travelling through the rubble, thus highlighting how they can be used as potential indicators of human presence. The sensor also detected various volatile organic compounds such as isoprene and acetone. It was found that when the subjects were asleep, there was a decreased level of ammonia, a phenomenon for which no explanation has been found so far. The researchers also found that with growing food withdrawal there was a build-up of acetone. Detectable molecules were also found in urine. When casualties are confined in a disastrous situation such as a collapsed building, the bodies release volatile metabolites through their skin, breath and bodily fluids, which might interact with the materials of the building. Such interactions modify with other factors such as heat, humidity and wind strength making the detection process more complex.