Richardson, 45, a member of Britain's Redgrave acting dynasty, fell during a private skiing lesson on a beginners' slope at Canada's Mont Tremblant resort on Monday. She died in New York on Wednesday, surrounded by her family.

Her death came about 10 years after those of singer-turned-politician Sonny Bono and Michael L Kennedy, son of assassinated Robert F Kennedy, who both died after skiing into trees at high speed while not wearing a helmet.

Richardson reportedly was not wearing a helmet.

Helmets, once rarely seen on skiers or snowboarders, have become increasingly popular, but the jury remains divided on their effectiveness and whether their use should be compulsory.

Some medical groups, including the Association of Quebec Emergency Room Doctors, have called for helmets to be mandatory, claiming 60 percent of head traumas could be avoided, and some countries are introducing laws requiring helmet use for children.

Jeff Hanle, a spokesman for the Aspen Skiing company, which runs resorts in Colorado, said all children under 12 at Aspen ski schools have to wear helmets, but otherwise it is not mandatory.

``We recommend helmet use for everyone, but we don't require it for adults. It is not for the industry to regulate,'' Hanle said. ``Children are growing up wearing helmets and they are continuing to use them as they grow, and more adults are also using them. The technology has got better, which has helped.''

But has it stopped injuries?

``It doesn't stop people from crashing, and it's hard to say if the injuries are less severe because of helmets,'' he said.

LAWS OVER HELMETS

Some skiers and snowboarders resist wearing helmets, complaining they are too hot or muffle sounds, while some fear they encourage risky behavior by giving a false sense of security.

Sales of helmets in Germany have doubled since a skiing accident in the Austrian resort of Styria in January that left one woman dead and German politician Dieter Althaus seriously injured, his life believed to have been saved because he wore a helmet.

Austria, which has recorded about 30 ski-related deaths this season, is introducing a law requiring all children under 14 to wear helmets on the slopes.

The Australian Ski Areas Association supports wearing helmets but says the decision is a personal or parental choice as helmets are most effective at providing protection at speeds of under 20 kmph and may not stop or reduce serious injuries at high speeds.

The National Ski Areas Association (NSAA) of the United States estimated 43 per cent of skiers and snowboarders wore helmets in the 2007-08 season, against 25 percent five years earlier.

The NSAA urges skiers and riders to wear a helmet but stresses that people's behavior on the slopes counts most. Skiing and snowboarding are no more dangerous than other high-energy participation sports, with 39 deaths on average a year.

The association cited researcher Jason Shealy, who studies ski-related injuries and found that recent research indicated helmets cut the incidence of head injuries by 30 to 50 per cent. But those were minor injuries, and wearing helmets had not cut fatalities.

``The increase in the use of helmets has not reduced the overall number of skiing fatalities,'' the NSAA said in a statement. ``More than half of the people involved in fatal accidents last season were wearing helmets.''