Gas attack

Windswept and treeless, the Orkney Islands lie off the northern tip of Scotland where the North Sea meets the Atlantic Ocean. Despite their remote location, the islands are a popular location for diving. Every year, about 3500 recreational divers explore Scapa Flow, attracted by the ghostly remains of German battleships scuttled in 1919 shortly after the surrender of the German fleet. The Orkney Islands are thus a fitting location for Heriot-Watt University’s International Centre for Island Technology, where Showcase grantholder Robert Forbes is working on a new monitoring device to improve diving safety.

Divers breathing compressed air must beware of a form of decompression sickness known as the bends. The longer a diver stays down and the deeper the dive, the more compressed gas is absorbed by the body. When the diver ascends, time must be allowed for the gases to be expelled slowly or they will form bubbles within body tissues. "Every time a diver does a dive, they end up with bubbles in the system," says Robert Forbes. "If the system gets overloaded, the bubbles can cause a decompression illness."

Decompression illness ranges from a skin rash to, in the worst case, death. Bubbles accumulating in the joints cause extreme discomfort (often causing divers to double up in pain – hence ‘the bends’), while bubbles in the nervous system can cause pins and needles, numbness, paralysis, or affect sight or speech.

As a marine biologist, Robert Forbes dives all over the world. "I’ve just finished a research project in Columbia looking at coral reefs," he says. "Before that I was in Malaysia, looking at the abundance of different species of sea cucumbers. But there is a big difference between tropical and temperate diving. Because of the cold in Orkney, the bloodflow in the peripheral tissues is much less, so you don’t lose the gas so quickly."

To make sure that enough time is spent decompressing underwater, standard tables and (for recreational divers) wrist computers have been devised that take into account the time and depth of the dive. "The problem with this is you can't guarantee a safe decompression for everyone. As everyone's physiology is different - some people are more prone to bubbling than others – and the standard tables don't always apply. So we add what we call the 'Jesus factor' - our best safety guess. If it's colder than normal you add time on, or if you have been working harder you add a depth increment. At the moment it is a matter of guesswork - which impinges on work performance and safety."

Bubbles in the system can only be detected after a dive, using a device called a Doppler stethoscope. "You make an audio recording of the bloodflow and then trained technicians listen to the recording," says Robert Forbes. "The problem is that you get a lot of background noise as well as signals from the bubbles in the blood vessel." The Showcase project is looking to replace the wrist monitors used by recreational divers with a system that will actually monitor the bubble count while on a dive. "What we’re doing is applying some new technology to process the sound signals," he says. "Rather than using the conventional frequencies, we can use different frequencies and come up with an automated method of counting the bubbles and determining what size they are - a more accurate method with less chance of human error."

This device will adapt technology used in sonar systems. "Sonar has the same problem as recording bloodflow – putting signal through water," says Robert Forbes. "What we can do is digitise the signals to clean up the data, and new algorithms have been developed that transform the data and get rid of background noise." Similar techniques are being used to improve audio recordings of heart signals.

The new device should make diving safer, but it will also help divers avoid any long-term problems associated with diving. "We have to use diving as a tool for our careers," says Robert Forbes. "We hope to be diving until we’re 55 or so."

See also

• Brainy babies: Article describing (Showcase funded research) on prenatal stimulation
• A bug’s death: Article describing (Showcase funded research) research on iron uptake in pathogenic bacteria
• Thinking big: Article describing (Showcase funded research) on the development of biodegradable polymers for use in drug delivery