How the body reacts to cold
Lookout! Issue 32, December 2014 – January 2015
At normal temperatures the heat generated by the body is carried by the blood to all regions of the body. The body automatically regulates its blood flow to control body temperature. Any excess heat is removed by transferring it to the outer layers for dissipation.
As the temperature of the environment falls, the outer layers of the body begin to cool. The body now reduces blood circulation to these outer regions, so that the cooling is not transferred to the important organs in the deeper regions of the body. Hands and feet feel cold because of the reduced blood supply to these areas. Shivering starts, as an involuntary muscular attempt to generate more body heat.
With further cooling, the inner core of the body begins to cool.* This is the beginning of hypothermia. The blood supply to the body’s outer regions is further reduced, as the body takes drastic measures to maintain the temperature of its vital organs. Shivering may decrease or stop. The organs in the core are now being affected.
As the brain cools, there is reduced control and consciousness is affected. Further cooling of the core will cause the organs to stop functioning. Consciousness is lost. Death will follow unless treatment is immediate and correctly given.
* While progressive loss of body heat can result in loss of consciousness and death, many victims perish much sooner when immersed suddenly in cold water. Cold shock can affect some, causing cardiac failure within a few minutes. Increased breathing rates can lead to dizziness, and the muscles cool rapidly. Immersion in cold water can cause such rapid loss of muscular function that a person loses the strength to board a raft or even operate a flare in minutes. A fit person in these circumstances quickly loses the ability to make even basic movements to help keep themselves afloat. There have been many recorded cases of drowning in less than 10 minutes – long before the body core temperature has started to drop or the person is affected by hypothermia.
Adapted from Safety in Small Craft, written by Mike Scanlan, Coastguard Boating Education Service.
Certain techniques can improve your chance of surviving long enough to be rescued:
- Wear a lifejacket
- A full lifejacket helps to keep the head and airway clear of the water, even when strength and mental capacity is waning. It will also make adopting heat loss-reducing postures much more stable.
- The more clothes you have on, the better
- Do not get undressed to enter the water. If there is time, add more layers. A person wearing two layers of woollen clothing will lose less than a quarter of the heat a person wearing only a swimsuit will lose. Wear as many layers of wool as possible, covered with a waterproof layer. The wool will trap warmer layers of water closer to the body.
- Try not to panic
- Panic can impair breathing and hasten the drowning process. Hyperventilation can occur when a person is unexpectedly immersed in the water. A mistimed breath can result in a laryngospasm, which sometimes results in loss of consciousness. A person who does not panic may simply have to cope with hyperventilation, which will eventually subside.
- Where possible, get out of the water
- In water the body loses heat 20 to 30 times faster than it does in air. Even if you feel colder out of the water, try to clamber on top of an overturned boat or any floating wreckage.
- If you are forced to stay in the water, adopt the HELP (heat escape lessening posture)
- Hold the arms tight against the chest, press the thighs together, and raise up the knees to protect the groin. This posture will increase survival time by nearly 50%. It will be most easy to adopt when wearing a lifejacket.
- Groups of three or more should adopt the huddle position
- The sides of the chests and the lower torsos are pressed together, arms hugging each other around the lifejackets. Intertwine legs as much as possible, and talk to one another. Children succumb to cold much more quickly than adults, and should be sandwiched in the middle of the group.
- Consider options before swimming to shore
- If you decide to swim for shore, consider that tests show an average person wearing a lifejacket and light clothing could swim about 1.85 kilometres in water of 10°C.
- In one Canadian case, a 20-year-old strong swimmer drowned within 5 minutes in 10°C waters. When deciding to swim for it, consider your swimming ability, the weakening effects of the cold and anxiety, and the huge overall heat loss that the swim will cause. If in any doubt, stay with the boat.