Cold water immersion
The effects of falling into cold water can be serious. The shock of sudden immersion into cold water can kill long before hypothermia.
- Victoria's coastal waters range from about 9.5°C in midwinter to about 22°C in midsummer
- The risk of drowning increases nearly five times if the water temperature is below 15°C
- Studies show up to 60% of fatalities due to cold water immersion occur in the first 15 minutes before the body core temperature cools to hypothermic levels
- Cold water carries heat away from the body 25 times more quickly than air with the same temperature
There are two main effects of cold water immersion: cold shock and hypothermia.
When a person falls into water less than 15°C the first reflex is to gasp and then hyperventilate, during which it is extremely difficult to hold breath. The heartbeat may become very fast and irregular during this time. There is a high danger of drowning if the head is not kept above water. It may take several minutes to regain control of breathing and be able to climb back aboard if this remains possible.
Strength and coordination weaken quickly in cold water, typically in ten to fifteen minutes, so it is important to inflate lifejackets and rafts, and set off EPIRBs quickly for the best chance of survival and rescue.
Prepare flares and signals next, so they are easy to access and deploy when help arrives.
Activity such as swimming will increase heat loss. Hypothermia commences when the body core temperature reduces, typically within an hour of immersion.
If you fall into cold Victorian waters you will generally have:
- 1 minute to get your breathing under control and keep your head out of the water
- 10 to 20 minutes of useful movement in which to get out of the water to prepare for rescue
- 1 to 3 hours before you become unconscious due to hypothermia.
The term 'hypothermia' means lowering deep-body or core temperature. 'Immersion hypothermia' is an acute type of hypothermia produced when a person is immersed in cold water.
An adult of average build could not expect to survive more than three hours of immersion in midwinter. The time is very short when you consider the time lost before a search and rescue operation is under way.
HELP and Huddle positions
HELP: If you're in the water alone, draw your knees towards your chest to stay as warm as possible. This is the 'heat escape lessening posture' (HELP).
Huddle: If you're in the water with other people, huddle together to reduce body heat loss.
The consumption of alcohol, attempting to swim or movement in the water will cause the body to use up heat rapidly, which will hasten the onset of hypothermia.
Key points for treating hypothermia
When recovering a person from cold water, keep them lying down if at all possible to reduce the load on the heart. Treat the cold person as for hypothermia and watch carefully for breathing difficulties due to intake of water.
- Remove the person from the cold-inducing environment
- Protect the person from cold wind
- Remove wet clothing if practical
- Warm victim with dry blankets, towels or skin-to-skin contact
- Warm the area of high heat loss, that is, head and neck, sides of chest, armpits, and groin. Do not warm, rub or massage limbs
- Observe the person for deterioration in condition
- Manage an unconscious person by placing them in the lateral position, making sure their airway is clear. Continue warming procedures
- Do not give the person alcohol
- Do not allow the person to walk around
- Seek medical assistance.
Watch this Marine and Safety Tasmania (MAST) video about cold water immersion.