Tough at the top Do rapid Everest ascents increase risk?

Sherpas in Nepal say the use of xenon gas and hypoxic tents could encourage inexperienced climbers to take on the mountain

- Hannah Ellis-Petersen and Gaurav Pokharel

There is nothing unusual about records being broken on Mount Everest. But last month, two sets of climbers turned heads with ascents that many had never thought possible: they went straight up from sea level to the world's highest summit in less than a week.

On 21 May, a team of four UK exspecial forces soldiers summited Everest having landed from London just over four days earlier. The next day, US-Ukrainian climber Andrew Ushakov said he had gone from New York to the top of Everest in under four days.

With Everest standing at a staggering 8,849 metres, scaling safely usually requires spending several weeks acclimatising at a lower altitude, normally Everest base camp, so the body can adjust to the lower level of oxygen.

Without this acclimatisation, most climbers would sicken or die in the final stages of summiting due to the thin oxygen levels above 8,000 metres, known as the "death zone". Altitude sickness accounts for almost as many deaths as falls and avalanches on Everest.

But using new methods and technologies, both the UK team and Ushakov acclimatised before even arriving on the mountain in Nepal, meaning they could skip base camp entirely.

Some expedition leaders claim preacclimatisation methods mark a new frontier in Everest mountaineering, increasing safety while reducing the two biggest blights on the mountain: rubbish and human waste.

However, others - including the Nepalese sherpas whose culture and employment is hugely reliant on leading expeditions up to the highest peak of the Himalayas - have expressed concern that speedier ascents could heavily affect the local economy.

There are also worries it will put even more pressure on the mountain, increasing the number of people ascending every season. Nepal typically issues about 400 permits for Everest each year, each valid for 90 days, with no rules for how long climbers spend on the mountain.