Trying to reach Everest's summit is a dangerous business. While more than 700 people have succeeded, 153 have died trying, or trying to return after succeeding. But that's not because the risk of avalanches (responsible for 50 or so deaths) or medical conditions such as fluid build-up caused by altitude have risen. If anything, bottled oxygen, modern drugs and familiarity with the terrain have reduced those dangers.
Paradoxically, expedition leaders now realise that one of the biggest obstacles to reaching the summit and returning safely is other climbers, either on guided expeditions or from "national" teams, climbing for their country's glory.
In fact the latter may be the most dangerous. The antics in recent years of teams from India, South Africa and Taiwan have all severely worried the more experienced leaders of paid-for, guided expeditions. "The greatest incompetence I have seen on mountains is national teams without guides," says Steve Bell, head of Himalayan Kingdom, an expedition company from Sheffield. This year he and two guides will take seven clients (each paying pounds 25,000) to try to reach the mountain's summit - but more importantly, to return safely.
Bell says that some national teams "show a lack of organisation and technique - not being roped together when going over terrain with crevasses, for instance. They don't take enough food and equipment, so they end up taking other people's. And they will go for the summit when the conditions or timing aren't right. There are countless examples of national teams being driven by some mad, patriotic fervour - as if lives are expendable as long as they get some people to the top.
This year attempts on the summit will be made by an Indian team and a Singaporean team - making their first attempt. Is Bell worried? "Only that they might get in the way, or might need to be rescued - because that has to come first above anything else," he says.
But the sheer volume of people on Everest can be deadly, simply because there isn't room enough for everyone when the mountain shows its vicious side. That was graphically demonstrated two years ago when a traffic jam on the highest mountain led to the deaths of expert and amateur climbers alike.
Key to this tale is a 20-metre stretch of steep rock and ice called the Hillary Step, on the mountain's south-east ridge - the most popular route to the summit - 8,790 metres above sea level and only 58 metres lower than the top.
The Step (named after Sir Edmund Hillary, who surmounted it on the way to the first ascent in 1953) is a steep, challenging section of rock and ice climbing: "a fair cow", as Hillary described it, "overhanging a little drop of 10,000ft".
But it's the only way up. Normally it is ascended by hauling oneself up on ropes. Two years ago however the ropes had blown away, and a queue built up as people waited for Anatoly Boukreev, a Russian mountaineering guide, to climb the Step and fix a rope at its top. Then all that would remain would be a determined plod upwards for another 50 metres to the summit.
But even for a talented climber like Boukreev, climbing the Step and fixing the rope took more than an hour. In that time, a queue of about 30 climbers - mainly members of guided expeditions paying thousands of dollars to reach the summit - built up.
Only one person can go up or come down at a time. Hauling oneself up the ropes takes time. Descent is a cautious procedure, not a free-ranging slide. All the time, the climber feels cold, and unbelievably exhausted, with a crushing headache. "The closest thing to drowning," is how Ed Viesturs, who climbed the ridge a few days later, described it. Sit down, and you might never find the determination to stand again.
The traffic jam made everyone's schedules slip, and Everest above 8,000 metres is no place to dawdle. Every minute, your body is literally dying, because there is not enough oxygen to support life. But that day people reached the summit and descended to the top of the Step only to find people below waiting to come up.
Meanwhile the weather worsened in the valley below. Within hours it was blowing subzero air at 100mph over the climbers, now hours behind a timetable that would let them reach the top and return below 8,000 metres.
Night fell, and in the ensuing chaos, seven people died, including Rob Hall, leader of one of the guided expeditions. A few days later a team making a film for the widescreen Imax format - now just opened in London's Trocadero and the National Museum of Film and Photography, Bradford - came across his frozen, lifeless body not far below the Step. Bringing it back was not an option. At that altitude it is all you can do to lift your feet, let alone a corpse.
The episode has been dissected repeatedly, notably by the book Into Thin Air by Jon Krakauer, one of Hall's clients. What's clear is that both Hall and the other guided expedition, led by Scott Fischer, should have turned their clients back long before the summit - perhaps even at the base of the Step, where the Taiwanese team, though many hours too late to make a sensible attempt on the summit before nightfall, was waiting to go up.
Bell has been there - he helped guide a group up Everest in 1993 - and knows the pitfalls. "We have always stuck strongly to having a time when we turn back, no matter what, and often to the chagrin of clients. It's a trade-off because you want to maximise their chance at the summit. But the priority is safety."
To the Imax cinemagoer, languidly eating popcorn in a warm, sea-level theatre, the view from the roof of the world may look tolerably interesting.
Will that lead to more people trying to get there? "I don't think it will discourage them," admits Jamling Norgay, son of Tenzing Norgay, the Sherpa who made the first ascent with Hillary. "It might even encourage them." That could be the most frightening fact of all.Reuse content