The soaring popularity of paragliding as a leisure pursuit and sport has prompted researchers to examine ways of making it safer.

A growing number of people are taking to the skies with distinctive oblong-shaped parachutes, favoured for their manoeuvrability. But there is increasing concern about the frequency of accidents caused by failure of paraglider lines, which are resulting in an estimated five deaths every year.

Manufacturers make the lines with the same high-performance fibres used in ship tow-ropes, but their strength and safety has never been systematically tested, according to Hossein Saidpour, who is leading a research project on paraglider safety.

Dr Saidpour's team in the department of product design and manufacture at Bournemouth University has found that exposure to sunlight, high and low temperatures, and high levels of stress due to dynamic manoeuvres, can cause one or more of the lines to snap after around 300 hours of flying.

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Paraglider pilots and clubs can lose track of the number of flying hours each line has notched up, especially if they have been bought second-hand.

The number of "safe" hours will also vary according to usage. Some paraglider pilots who take part in competitions regularly make radical moves such as one known as the "Big Ear", in which the canopy is suddenly deflated and then rapidly inflated. This places rapid high shock loads on the lines, which can lead to catastrophic collapse of the paraglider if one of them snaps.

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Research has shown that the majority of breakage failures take place at the pilot end of the line, where it is often bent sharply leading to a high concentration of stress and reducing the line strength by up to 75 per cent for heavily-used paragliders.

The Bournemouth project, financed by manufacturers and the British Hang- gliding and Paragliding Association, is preparing a formula for improving line design and materials, and developing equipment for testing line strength.

"So far the results have been very promising and we are confident that we will soon be able to make positive recommendations to reduce the risk of tragedies occurring in the future," Dr Saidpour said.