Breath of fresh air

An Israeli engineer has developed a breathing device that he claims will allow divers to dispense with oxygen tanks.

It could also be used to supply air to submarines and future underwater habitats such as hotels or scientific research facilities, according to developer Alan Bodner.

The technology collects the small quantities of air that are present in water, mimicking the way fish breathe. It has already attracted interest from the Israeli Navy, as well as diving equipment manufacturers, he said. The Israel Ministry of Industry and Commerce has provided finance for the project.

The use of oxygen tanks is the biggest single limitation on the amount of time a diver can stay underwater. As the tank empties, it also changes the diver’s balance and makes it harder to control movement. Refuelling tanks with oxygen is also a costly and timeconsuming process.

Nuclear submarines currently use electrolysis to obtain oxygen from water, though this requires large amounts of energy and makes such a system impractical for smaller vessels which must instead use oxygen tanks.

Bodner’s design consists of a lightweight cylindrical device, smaller and lighter than a current oxygen tank. The system is based on Henry’s Law, which states that the amount of gas that can be dissolved in a liquid is proportional to the pressure on the liquid. Lowering pressure releases gas.

Water is pumped into the cylinder where a battery-powered centrifuge spins the water rapidly. This causes the water to be thrown to the outside wall of the cylinder, leaving a vacuum in the middle. The resulting reduction in pressure extracts dissolved air, which is transported to an air bag for the diver to breathe. The water is then expelled.

A one kilo lithium battery can currently provide an hour of diving time, though Bodner hopes to extend this to several hours.

‘The diver will be able to adjust the directions of the intake and out-take vents to use the flow as a propulsion method in a similar way to a Harrier jet, should he or she wish to do so,’ added Bodner.

The device is best suited to closed-circuit diving, where gas is continuously recycled by cleansing it of carbon dioxide after exhalation before adding oxygen from a tank so it can be re-inhaled.

In conventional open-circuit diving, exhaled breath is wasted by venting the bulk of it into the surrounding water. This process consumes a significantly greater amount of air, which would involve extracting air from large volumes of water.