2 - Cold water hazards and their effects: knowledge that can improve survival chances
An understanding of how your body reacts to cold air or water exposure, and knowing the steps you can take to help your body delay the damaging effects of cold stress, will help you stay alive.
If you need to abandon your ship you should, if possible, avoid going into cold water at all. Cold water represents a much greater risk than cold air, partly because water takes heat away from the body much faster than air. Human beings cool four to five times faster in water than in air at the same temperature – and the colder the water is the more likely it is that you will suffer the physical reactions and medical problems described below. Therefore, you should try to enter survival or rescue craft directly, without entering the water.
The major threats of cold water immersion are:
- collapse just before, during, or after rescue.
Four stages of immersion have been identified. Each is associated with particular risks, and it helps to understand these and so be better able to deal with them.
Initial responses to immersion in cold water may include:
- inability to hold your breath
- an involuntary gasp, followed by uncontrollable breathing
- increased stress placed on your heart.
These responses are caused by the sudden fall in skin temperature. It is important to remember that they will last only about three minutes and will then ease. Remember too that, at this stage:
- the fitter you are, the smaller the initial responses to cold water immersion and the smaller the chance of you experiencing heart problems
- wearing an appropriate lifejacket, properly fitted, will decrease the risk by helping to keep your airway clear of the water and reducing the need for you to exercise during this critical period
- wearing appropriate protective clothing will also decrease the risk by slowing the rate of skin cooling and thereby the size of the initial responses
- if you experience initial responses you should stay still for the first few minutes of immersion, doing as little as possible until you have regained control of your breathing: a lifejacket or other source of buoyancy will help you do this
- the period of possible self-rescue starts immediately after the initial responses (if experienced), and before hypothermia sets in.
Short term immersion effects follow the initial responses. During this phase cooling of the muscles and nerves close to the surface of the skin – particularly in the limbs – can lead to inability to perform physical tasks. Swimming ability will be significantly impaired. (Swimming accelerates the rate of cooling in any event.) It follows that:
- essential survival action that requires grip strength and/or manual dexterity – such as adjusting clothing or your lifejacket, or locating a lifejacket whistle or turning on a light, for example – should be taken as soon as possible after the initial responses to cold water immersion have passed
- you should not attempt to swim unless it is to reach a fellow survivor or a nearby shore, craft, or other floating object onto which you can hold or climb.
Stay calm. Evaluate your options. Can you reach a shore or floating object – knowing that your swimming ability will be less than normal? If not, stay where you are, conserve body heat (see below), and await rescue.
Long-term immersion effects include a fall in deep body temperature (a cooling of your vital organs such as your heart, lungs and brain) to hypothermic levels. However, the rate at which your deep body temperature falls depends on many factors, including the clothing you are wearing, your physique, and whether or not you exercise in the water – by swimming, for example. Your temperature will fall more slowly if you:
- wear several layers of clothing, including head covering – especially under a waterproof outer layer such as an immersion suit
- keep still – this is greatly facilitated by wearing a lifejacket.
The rescue phase is the fourth stage of immersion you should focus on. A significant percentage of people die just before they are rescued; during their rescue; or just after it. This may be because of:
- the way in which they are rescued
- relaxing too soon
- loss of buoyancy – actions such as waving, etc. may release air trapped in clothing. Again, wearing a lifejacket removes this threat.
It follows that:
- you should stay still in the water: blow a whistle or shout to attract attention – but do not wave unless you are wearing a lifejacket or have some other aid to flotation
- the rescue itself should be carried out appropriately (see the rescue phase, below)
- you should maintain your determination to survive throughout: do not relax too soon.
1By medical convention clinical hypothermia is considered present when the "deep", or "core", body temperature falls below 35°C (95°F): that is, when about 2°C (3.5°F) has been lost. With continued cooling consciousness will be progressively impaired and then lost; eventually death will follow. However, in cold water death from hypothermia itself is relatively rare. More of a threat is the loss of heat from the muscles: incapacitation may then lead to the casualty being unable to keep their airway – the mouth and/or nose – clear of the water, so that they drown. Hence the importance of being well clothed and wearing a correctly fitted and adjusted lifejacket.