Ring of Confidence

By Andy Coghlan THE world's newest and most compact breathing apparatus is being put through its paces in a mock emergency next week. The device stores air, not in a cylinder, but in a doughnut-shaped "toroid".

Researchers working at Britain's Defence Evaluation Research Agency (DERA) in Farnborough, Hampshire, claim the novel design will be safer and easier to use and could revolutionise firefighting, skin diving and other activities where people must wear breathing equipment.

Traditional cylinders are fraught with problems. When worn by firefighters the cylinder sticks up so much that it becomes nearly impossible to carry people to safety. They also make it difficult for emergency workers to get through small openings and narrow gaps.

The valves on a cylinder are in a vulnerable position and have to be protected to avoid potentially lethal blowouts. In the toroid the valves are tucked safely away in the middle of the doughnut.

Cylinders are also cumbersome. All the weight of the cylinder-up to 12 kilograms-rests on the shoulders, and it has to be mounted on a sturdy metal plate to stop it moving around. The toroid requires no metal plate and fits neatly into a canvas satchel. "If you wear our toroid, you can transfer most of the weight onto the hips instead of the shoulders, which is snugger and more comfortable," says John Cook, head of the DERA development team.

The toroid idea was brought to DERA's attention by Brian Richards of Life Support Engineering, based in Storrington, Sussex. Richards looped a cylinder back on itself to create the toroid. The design uses aramid fibres, more commonly known as Kevlar, to strengthen the vessel walls. This has allowed them to succeed where earlier attempts to use a toroid have failed. "All previous versions used only metal and always came up too heavy," says Cook.

Complex forces within a toroid mean that safely accommodating air pressurised to the usual 207 atmospheres requires the inner rim of the doughnut to be 50 per cent thicker than the outer rim. But manufacturing a shell with a varying thickness of metal was too costly, says Cook.

So although the aluminium casing is the same thickness throughout, the developers have wound a spiral of aramid fibres around the exterior-like the lagging around a pipe to stop it freezing in winter. The slim fibres are bunched closer together at the inner rim, and so counterbalance the extra stress.

Cook is confident that the finished toroid will weigh around 6 kilograms-comparable with the lightest upright breathing apparatus on the market.

Cook and Richards have patented the design, and are already negotiating with commercial suppliers of breathing equipment. DERA and Life Support Engineering would both receive royalties for each item sold. Cook says that the potential market for the breathing apparatus is enormous, with 2 million units sold each year at a value of some £500 million.

Ring of Confidence 1

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