Search and Rescue — Chromatography Can Help

When a natural disaster strikes in the form of an earthquake or landslide it is often a race against time to rescue the people trapped beneath fallen buildings or other debris. Thermal imaging, sound detection and optical fibre cameras are all used to detect trapped people. But it is often to search and rescue (SAR) dogs that the authorities turn — with highly trained dogs flown to disaster areas worldwide to help find missing people.

But this is not without its cost. Training a SAR dog takes many years and is expensive. The dogs can also suffer similar effects to humans involved in such environments — becoming understandably stressed and physically tired — their health has to be constantly monitored. The pursuit of a suitable canine replacement — being more cost effective and capable of operating away from a handler — is ongoing, and a recent study has looked at some of the compounds a device should be capable of detecting.

Human volatiles

Even though SAR dogs can find humans, we don’t know exactly how they do it — which scents or molecules they use is still a mystery. So if we want to replace the dogs we have to ascertain what compounds can be used to indicate the presence of a human in a collapsed building. It was with this aim that a team from the Airforce Research Laboratory in Ohio, USA, had a look at what human-derived VOCs could be used to indicate the presence of people.

In a report titled ‘Detection of volatile organic compounds indicative of human presence in the air’ and published in the Journal of Separation Science, the authors sampled air from occupied rooms, unoccupied indoor spaces (hallways or conference rooms) and from outdoor spaces.

The air was sampled using thermal desorption tubes, with about a litre of air collected. Following thermal desorption, the VOCs were separated using gas chromatography with a thermal gradient program ranging from 40?C to 240?C at 10?C / min with a final hold at 240?C for 20 minutes. The separated VOCs were then analysed and identified using mass spectrometry.

The use of thermal desorption for sampling and analysing VOCs is discussed in detail in this Chromatography Today article, Trace Level VOC Analysis in Different Sample Matrices.

Endogenous and exogenous smells

The team found that isoprene (most abundant hydrocarbon in the breath of humans) was that best indicator of a human presence amongst the endogenous VOCs. The research suggests that other endogenous sources of VOCs don’t show a correlation with human occupancy. Instead the team found that a number of exogenous VOCs (from foods, deodorants and other consumer products) were detected at elevated levels in occupied rooms.

From these results the team report that

‘isoprene and many exogenous VOCs consumed by humans are emitted at levels suf?cient for detection in the air, which may be indicative of human occupancy or presence’.

So one day, eating chilli nachos may save your life.

Image by jeffreyw via Wikimedia Commons