KEY POINTS
- Keeping a casualty warm and dry is potentially life saving after a heavy crash
- A normal body temperature helps blood clot more effectively, reducing bleeding and improving prognosis.
- Canopies make very good blankets.
EXPLANATION
When you reach the casualty, think about sheltering them from the elements. It is one of the simplest and most important things that you can do to help.
Keeping a casualty warm and comfortable is not just a compassionate act. It helps stop further injury, as blood clotting worsens significantly when body temperature drops.
An injured casualty will cool rapidly, even if the air is warm around.
Think about heat loss to the ground, as well as to the air. Try to have them out of the wind, with something underneath them.
Foil ‘space blankets’ aren’t particularly good: they are designed to reflect back radiant heat, but a cold casualty won’t be producing very much heat to radiate back. A canopy, or even bubble wrap, are much better as they trap a layer of air between the casualty and the environment.
If they are wet, either remove the wet clothes, or wrap them in something non-breathable to form a vapour blanket.
Sheltering from Wind and Precipitation
Wind strips away the thin layer of warm air that normally sits next to the skin, dramatically increasing heat loss even when the air temperature is not particularly low. A casualty lying in even a light breeze can lose body heat two to five times faster than one in still air. Always look for natural windbreaks first: the lee side of a wall, a large rock, a dense bush, or a dip in the ground. If none is available, build one from whatever is to hand, such as a rucksack, a bicycle, or a pile of branches. Position the casualty behind the barrier, not in front of it, and make sure the barrier is tall enough to cover the whole body, especially the head and shoulders.
Rain and snow bring two additional problems: they wet clothing and they cause evaporative cooling as the moisture dries. Wet fabric conducts heat away from the body roughly 25 times faster than dry fabric. If you cannot get the casualty fully under cover, use a canopy, a plastic sheet, a bin bag, or even a large map case to create a simple roof. Angle it so that water runs away from the casualty, not onto them. For light rain, a single layer held above the body is often enough; for driving rain, you need both an overhead barrier and a side wall on the windward side. Keep the covering off the casualty’s skin where possible, because a wet layer in direct contact with skin accelerates cooling even further.
When working in snow, do not let the casualty lie directly on the surface. Snow is a surprisingly good insulator, but it is also cold and wet. Dig down to the ground if time allows, or place as many dry materials as possible between the casualty and the snow. Packed snow can be shaped into a low wall around the casualty to break the wind, but do not bury them or let snow fall onto their clothing. Each time you move the casualty, check that their clothing has not become damp from contact with the ground.
Insulating the Casualty from the Ground
Heat loss into the ground is commonly underestimated. Cold ground, concrete, or even damp grass will conduct heat away from the casualty far more efficiently than air of the same temperature. A casualty lying on bare earth can lose a dangerous amount of core heat in under thirty minutes, even on a mild day. Always place something underneath them before you do anything else. A folded canopy, a rucksack with the contents removed, a sleeping mat, a car seat cushion, cardboard, or a thick layer of dry leaves and branches all work reasonably well.
The insulation should be as continuous as possible. Gaps under the shoulders, hips, or heels become cold spots that draw heat from the whole body. If you only have limited material, prioritise the torso and upper legs, as these are the areas with the greatest blood flow. A casualty who is conscious may be able to lie on their side with their knees drawn up, which reduces the surface area in contact with the ground. If they are unconscious, place them in the recovery position and build the insulation up around the back, buttocks, and the side of the head that touches the ground.
In urban or roadside settings, look for building materials such as timber pallets, carpet offcuts, or even a thick layer of newspaper. Newspaper is surprisingly effective when used in multiple layers and kept dry. If you have access to a vehicle, remove a seat cushion or use the boot liner as an improvised ground pad. The key principle is the same in every environment: separate the casualty from the cold surface with as much dry, compressible material as you can find.
Protecting the Head, Neck, and Core
The head and neck account for a disproportionate share of total body heat loss, particularly in a casualty who is lying still. In cold conditions, an uncovered head can lose up to half of the body’s heat production. Put a hat, hood, scarf, or any dry fabric over the casualty’s head as soon as possible. If you have nothing else, use your own clothing or hold your hands over their head and ears. Even a thin layer makes a measurable difference. The neck also has large blood vessels close to the surface, so wrap a scarf, collar, or folded cloth loosely around it, making sure not to restrict breathing or blood flow.
Prioritise the core over the limbs. The body will naturally reduce blood flow to the arms and legs to protect the heart, lungs, and brain, so adding insulation to the torso has a greater effect on survival than putting gloves on cold hands. Wrap a jacket, blanket, or canopy around the chest and abdomen first, then cover the groin and upper thighs, where major blood vessels run close to the surface. Only after the core is protected should you attend to the hands and feet. If you have only one warm item, put it on the casualty’s torso, not their extremities.
Do not forget that a casualty who has been lying on cold ground may have cooled from underneath as well as from above. Insulation above the body is not enough. Check that the layers under the back, head, and hips are still in place each time you reposition the casualty. A common mistake is to wrap someone in a blanket on top while they continue to lose heat through the ground beneath them. Treat both surfaces as equally important.
Improvised Barriers and Vapour Layers
A vapour barrier is a non-breathable layer placed directly over damp clothing or skin that traps moisture and stops evaporative heat loss. This is not the same as a conventional blanket, which works by trapping warm air. Plastic sheeting, bin bags, a large poly bag, or even a survival bag can act as a vapour barrier. The casualty will feel clammy inside it, but the trapped humid air quickly reaches a stable temperature and then acts as an insulating layer. This is particularly useful when the casualty is already wet and you cannot remove their clothing safely.
To make an effective vapour barrier, enclose as much of the casualty as possible without covering the face. Slit a bin bag down one side and one bottom edge to open it into a flat sheet, then wrap it around the casualty, tucking the edges underneath. If you have two bags, put one over the legs and lower body and another over the torso and arms. Seal the neck and wrists loosely with tape or string, but leave an opening for their mouth and nose. Over the vapour barrier, add any dry insulating layers you have, such as a canopy, clothing, or a blanket. The vapour barrier must be on the inside, next to the skin or wet clothing, and the dry insulation on the outside.
Canopies, bubble wrap, carpet underlay, and reflective windscreen shades can all be used as improvised outer layers. Bubble wrap works well because the trapped air pockets provide insulation and the plastic acts as a vapour barrier. If you have a large piece, wrap it around the casualty with the bubbles facing inward. Tape the seams with gaffer tape or tie them with cord to stop the wind getting underneath.
- Always keep the casualty’s airway clear and visible.
- Check the wrapping every few minutes for signs of overheating or breathing difficulty.
- Do not use a vapour barrier if the casualty is already dangerously hot or has heatstroke.