Why hypothermia is a year-round risk on the hills

Hypothermia is not just a winter problem. On UK hills and ridges, the combination of wind, rain, sweat and a sudden stop can chill a walker quickly, even in summer. A temperature of 10°C with 40mph wind feels closer to freezing. Add wet clothing and fatigue, and your body loses heat faster than it can make it. Ridges are especially unforgiving because there is little shelter and the wind hits from every direction. The classic scenario is a fit walker in a lightweight shell who stops for lunch after a long climb, gets cold, and then cannot get warm again. Recognising the early signs and acting fast is far more effective than trying to rewarm someone who has become seriously cold.

Spot the early signs before shivering stops

Mild hypothermia is easy to miss. The casualty may say they are fine, but they are shivering persistently, have cold hands and pale skin, and are becoming clumsy. Watch for the "umbles": grumbles, mumbles, fumbles and stumbles. They may become quiet, apathetic or unusually argumentative. Their speech may slur, they may struggle with zips or map reading, and they may make poor decisions about the route. Shivering is a good sign because it means the body is still trying to warm itself. If shivering stops, that is a serious warning: the body has run out of energy to generate heat.

In moderate hypothermia, the casualty may be confused, drowsy, and have slow, shallow breathing. They may not shiver at all. In severe cases, they become unconscious, their pulse and breathing are very slow, and their skin may be cold and blue. Do not assume someone is just tired or "a bit quiet". If they are cold and acting out of character, treat it as hypothermia.

Immediate actions on the hill

Stop as soon as you notice the signs. Do not try to walk the casualty to safety unless it is the only option. Exercise pumps cold blood from the limbs back to the core, which can make the situation worse. Get out of the wind and rain immediately. A bothy bag, tent, bivvy bag or even a group shelter behind a rock will make a huge difference. Insulate the casualty from the ground with rucksacks, rope or spare clothing. Remove wet clothing and replace it with dry layers. If they are soaked, get them into a sleeping bag or foil blanket, and put a hat on them. Handle them gently and keep them horizontal.

• Do not rub their limbs, put them in a hot bath, or give them alcohol.
• Do give warm, sweet drinks if they are fully conscious and can swallow. No caffeine if possible.
• Do share body heat inside a sleeping bag if you have one.
• Do use wrapped warm water bottles or hand warmers on the trunk, not directly on the skin.

Warm them gradually, core first

The aim is to warm the core slowly, not the extremities. If you warm the arms and legs first, cold blood from the limbs can return to the heart and drop the core temperature further. Focus on the chest, back and head. Keep the casualty still and monitor their breathing and level of consciousness. If they are shivering, let it happen—it is generating heat. If they are not shivering, use external heat. A second person in a sleeping bag with them is one of the most effective field techniques. Keep checking for changes every few minutes. If they become unconscious but are breathing, place them in the recovery position to protect the airway. If breathing stops, start CPR and do not stop until help arrives or you are exhausted.

Shelter, signals and getting help

If the casualty is moderate or severe, you need professional help. Call 999, ask for the police, and then ask for mountain rescue. Give a clear grid reference, the number of people in your group, the casualty's condition, and what clothing and shelter you have. If you have no signal, send two people for help if it is safe to do so, but never leave the casualty alone. Use a whistle: six blasts, pause, repeat. Use a torch or mobile phone screen to signal. Keep the casualty sheltered and warm while you wait. Note the time and any changes in their condition so you can pass accurate information to the rescue team.

Prevention on ridge days

Most hypothermia is preventable. Check the forecast for wind, rain, temperature and visibility, and be honest about your group's experience. Wear layers: a base layer that moves sweat, an insulating mid-layer, and a windproof and waterproof shell. Carry spare gloves, a hat, a dry base layer and an emergency shelter even on a short ridge route. Eat and drink regularly. Pace yourself to avoid heavy sweating, and put layers on before you feel cold. On exposed ridges, take breaks in shelter, not on the skyline. Know your escape routes and be willing to turn back. Finally, look after each other: if someone is quiet, shivering or falling behind, stop and deal with it early. That is the most important skill on any hill day.