Thin Air: What Altitude Does to People and Engines

Vehicle travel makes altitude uniquely dangerous, because it allows you to gain three thousand metres in an afternoon without effort. A walker earns acclimatisation by the day. A driver arrives at 4,500 metres with a headache and a plan to sleep there, which is precisely the way altitude sickness becomes serious.

What happens to people

Above roughly 2,500 metres, mild symptoms are common: headache, poor sleep, breathlessness on exertion, loss of appetite. Acute mountain sickness is the moderate form and it is a warning, not an inconvenience. The two severe forms, fluid on the lungs and swelling of the brain, are rare but life-threatening and have one reliable treatment, which is to descend immediately.

The rules are simple and they work. Above 3,000 metres, increase your sleeping altitude by no more than 500 metres a day, and take a rest day every 1,000. Climb high during the day and come back down to sleep. Drink far more than you feel like. Avoid alcohol for the first days. Treat any symptom that does not improve with rest as a reason to descend, and never let somebody with worsening symptoms sleep higher than they did the night before.

What happens to engines

Naturally aspirated engines lose roughly 10 percent of their power per 1,000 metres of altitude. At 4,000 metres, that is a vehicle with 60 percent of its sea level output, driving on steep gravel, fully loaded. Plan the day's distance around that rather than around the map.

Turbocharged engines fare much better, because the turbo compensates for thinner air, though they run hotter and work harder. Diesel engines generally cope better than petrol. Older carburetted petrol engines run rich and may need jetting for extended high altitude work. All engines need more cooling attention on long climbs, and automatic transmissions in particular.

Climb high, sleep low. It is the oldest rule in mountaineering and it applies just as much when the climbing is done by a vehicle.

Cooking and water

Water boils at about 86 degrees at 4,000 metres, which means boiling does not sterilise as reliably and food takes far longer to cook. Pasta that takes ten minutes at sea level may take twenty-five; dried beans become impractical. A pressure cooker is the classic high altitude solution and saves fuel as well as time. For water treatment, use a filter or chemical treatment rather than relying on a rolling boil.

Canister stoves lose performance in cold thin air; liquid fuel stoves that can be pressurised are more reliable high up. Whatever you use, allow more fuel than the flat-land calculation suggests.

Cold and sun together

High altitude combines intense solar radiation with very low air temperature. Sunburn happens through cloud and reflects off snow onto places that never normally see the sun. Sunglasses with proper protection are medical equipment, not an accessory, because snow blindness is genuinely disabling. At the same time, the temperature swing between midday sun and a clear night can exceed 30 degrees, which puts the layer system to work in both directions in a single day.

Planning the route

Look at the profile, not the distance. A route with a 4,800 metre pass in the middle needs to be planned around where you will sleep on either side of it, and around the fact that passes close with weather at short notice. Carry more food and fuel than the distance suggests, because a closed pass means waiting or a long detour.

Know where the nearest lower ground is at all times. In an altitude emergency, the treatment is descent, at night, in the dark if necessary, and the party that has already identified the road down by 1,000 metres will act far faster than the party working it out with a headache and a torch.

Questions we get asked

Does acetazolamide help?

It can speed acclimatisation and is commonly prescribed for rapid ascent profiles, which vehicle travel usually is. It is a prescription medicine with side effects, so discuss it with a travel doctor before the trip rather than buying it at the trailhead.

How high can a standard vehicle go?

Roads reach above 5,600 metres in Asia and South America and ordinary vehicles drive them daily. The limits are power, cooling and fuel quality rather than any hard ceiling, and turbocharged diesels manage best.

What about sleeping in the vehicle at altitude?

It is warmer and more sheltered than a tent, which helps. Ventilate properly: any combustion heater or stove in a closed vehicle at altitude is a carbon monoxide risk, and thin air makes the consequences worse.