In May 2004, British climber Mr Neil McNab and his partner Mr Andy Perkins trudged through a high-altitude blizzard raging across the Denali Pass, 6,000m above sea level on the flanks of Alaska’s Mount McKinley, the highest mountain peak in North America. They were searching for a fallen Korean climber who’d been left for dead during his summit attempt, hours earlier. “His jacket was open, his exposed hand looked frozen, and his head was stuck to the ground,” recalls Mr McNab, an IFMGA/UIAGM high-mountain guide and ISIA/ISTD ski and snowboard teacher. “As Andy searched the body for a pulse, he suddenly woke up, sat up, shouted and then passed out again,” says Mr McNab. “We no longer had a body to deal with. We now had a rescue on our hands.”

It was the beginning of an 18-hour epic that saw Messrs McNab and Perkins lower the climber 1,000m down the mountain to safety, saving his life and giving up their own summit attempt in the process. For their efforts, the pair were rewarded with the Medal of Valor by the US Government.

Mountaineering is full of such stories, and the statistics can make terrifying reading. Before 2007, for example, the death rate on Everest among those attempting the summit was a chilling one in 10. And yet, the “because it’s there” mania that drove the early tweed-clad pioneers can overtake anybody. Today, with more people climbing than ever before and tour companies offering packages, ticking off the summit of your dreams has never been easier. Whether you’re planning to conquer one the UK’s own deceptively challenging climbs, such as Ben Nevis or Snowden, or harbour aspirations to summit the mighty Chomolungma herself (that’s Everest to you and me), the correct preparation and the right decision-making on the climb itself could be the difference between success and failure – or even life and death.

“Climbing is like solving a puzzle,” says Mr McNab. “The easier the climb, the more ways of solving the puzzle there are. The hardest climbs have only one solution, and in those cases you either have the skills to solve the sequence or you don’t.”

There is a mass of mountain literature available outlining different approaches and angles of attack, while maps and, increasingly, Google Earth can be used to study heights, gradients, proximity of one peak to another, and the distance to suitable base camps and access points. Every mountain will also have an optimum season – something else your expedition should take into consideration. The annual Everest season, for example, falls in May to take advantage of the brief period that marks the beginning of the Asian monsoon when the summit winds diminish to a survivable velocity.

Climbing mountains is also a high-performance endurance activity, so any of the classic endurance sports – such as running, cycling, rowing or even climbing hills or smaller mountains – is a great start.

On the climb itself, the importance of acclimatisation comes down to a simple physical equation. The higher you go, the less oxygen there is. Your body uses oxygen to feed your muscles, and the harder you work, the more it needs. With less oxygen available at higher altitudes, everything has to work harder and your physical and mental abilities are drastically reduced.

At higher altitudes, above 4,000m, the effect is even more insidious – as well as shortness of breath, headaches, lassitude and dizziness, more serious conditions can develop. Acute mountain sickness (AMS), high-altitude pulmonary oedema (HAPE) or high-altitude cerebral oedema (HAPE) can all be fatal.

You can mitigate these potentially disastrous effects by being as fit as possible and by carefully planning your own acclimatisation process to suit your own expedition. “Go too high too quickly or too soon, and the effects will be the same,” says Mr McNab. “The only solution is to descend as soon as possible. Acclimatisation can take weeks depending on how high you intend to go, so a couple of days won’t do it.”

Unless you’re on an old-style Himalayan expedition staffed with porters and sherpas, you’re likely to be carrying everything yourself – rope, harness, rack of equipment, crampons, ice axe, clothing for warm and cold conditions, food and water. If you’re climbing a classic vertical big wall such as The Nose on El Capitan in California’s Yosemite National Park, which typically takes three-to-five days, you might also need to bring a portaledge to sleep on.

Above all, keeping the weight down will give you the marginal gain that could make all the difference, says Mr McNab, “Working hard at altitude can be like climbing five flights of stairs while breathing through a straw. Any unnecessary weight just makes it harder.”

So think like the intrepid Mr Jacques Balmat, who on 5 June 1786, armed only with a bottle of brandy and a baguette, decided to spend the night atop the Grand Mulets at a height of 3,000m. In doing so, he found a route up Mont Blanc that meant he would be part of the first summit duo on 8 August 1786.

Bad weather is without question the biggest single obstacle between success and failure in any climbing expedition. Not for nothing do Himalayan expeditions rely so heavily on the weather “window” – typically, a five-to-seven-day good-weather period, enabling summit teams to ascend and descend in enough time to escape danger. Even then, things can go badly wrong, as it did during the 1996 Everest disaster, when eight climbers died after descending from the summit too late into the teeth of a howling blizzard.

At lower altitudes, the weather can be equally critical. “Generally, climbing mountains in bad weather is a really bad idea,” says Mr McNab. “If the weather is bad, conditions in general won’t get better the higher you go and trying to navigate around glaciers or exposed slopes in zero visibility really isn’t that much fun.”

The best defence against disaster is to keep a constant eye on the weather and be prepared to make smart decisions and turn back if the weather conditions do worsen. Better to stay safe and come back to fight another day than put yourself or any rescuers in unnecessary peril.

“Getting to the top is optional. Getting down is mandatory,” says Mr Ed Visteurs, the only American to have climbed all 14 of the world’s 8,000m peaks. Yet post-summit descents have been the cause of some of the most infamous mishaps in mountaineering history, from the accident that befell the Whymper party on the way down from the first descent of the Matterhorn (four out of the nine-strong party were lost), to modern catastrophes such as the death of Briton Mr David Sharp, who collapsed on what was thought to be his descent from Everest’s summit.

A classic high-altitude mistake among mountaineers succumbing to summit fever is to take too long to reach the top and use all their oxygen in the process, thus meaning they don’t have enough to safely descend, as happened to Mr Sharp. Above all, rational decision-making is essential – not easy in states of extreme fatigue at oxygen-starved altitudes.

“Everything is more difficult at altitude,” saya Mr McNab. “Thinking clearly gets harder and harder the more tired you get. But making the right decision can save your life.”

In particular, adhere to summit windows, and always turn back if you won’t be able to reach the top in your allotted time. Messrs Stuart Hutchison, John Taske and Lou Kasischke survived the 1996 Everest disaster because they turned back after recognising a bottleneck of climbers attempting to negotiate the Hillary Step would critically delay their own summit attempts. Some of their other colleagues continued – and paid with their lives.

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