NSW Maritme News

Cold Water

Cold Water

Most people know that cold water is dangerous – but many don’t realise just how dangerous it can be. With winter now upon us, it is a good time to review a few things about the dangers of cold water and what precautions can be taken to guard against it.

Cold is not just a number

It is surprising how cold water feels. Imagine you are in a 15 degree room. You touch a wooden railing with your bare hand – it hardly feels cold (wood is a poor conductor of heat). You then touch a metal railing – and immediately notice the difference. Water, being a very good conductor of heat, is just like the metal railing. What’s worse, is that if you fall in the water, that cold ‘metal railing’ is all over you, draining heat from your body many times faster than would air at a similar temperature.

It can take your breath away – literally

The first thing most people think of is hypothermia – the cooling of the body’s core below its normal temperature. While this is dangerous, it isn’t your most immediate problem if you fall in.

The first thing that happens if you fall in cold water is ‘cold shock’. This causes, among other things, rapid uncontrolled breathing and a racing heartbeat. Vulnerable people may even have a heart attack. The first signs of cold shock can be felt in some people in water as warm as 25 degrees, and most people really feel it under 20 degrees. At around 15 degrees, it becomes quite dangerous – especially if the water is choppy.

While the worst effects of cold shock only last a minute or two after entering the water, they can cause people to swallow water or panic – and even quite reasonable swimmers have drowned because of cold shock almost immediately after suddenly being forced into water. A lifejacket is a huge advantage when dealing with cold shock.

It allows you to keep your head safely above water while you regain your composure.
Once the affects of cold shock have passed, a person in cold water may feel relatively comfortable. However, within minutes (depending on just how cold the water is), they will begin to lose manual dexterity and muscle strength. This will quickly reduce a person’s capacity for self help, and will place significant limitations on their ability to float unaided or swim any distance. A person in this situation may exhaust themselves and drown well before hypothermia sets in.

Hypothermia, the third stage, begins with shivering and mental confusion and eventually leads to drowning as a result of impaired consciousness.

Wearing a lifejacket will buy extra survival time for a person forced to remain in the water for extended periods – greatly enhancing their chances of rescue. A lifejacket will support an exhausted swimmer, and will reduce the rate of heat loss by providing some direct insulation against the water and by reducing the need for body movement.

You can’t rely on the air temperature

As most early season beach-goers will attest, just because it is warm and sunny outside doesn’t mean the water is warm too. The problem is that water takes a long time to warm or cool in comparison to the air – and this can mean long lags between seasonal weather and prevailing water temperatures, especially in the ocean.

Other situations where the water might be much colder than the air occur in rivers and lakes. Cold water released from upstream storages can remain colder than normal for literally hundreds of kilometres downstream. On large lakes and reservoirs, the summer sun typically only heats the surface layers, leaving much colder water lurking deeper down – strong winds can easily displace the warmer surface layer to one side, bringing the cold water to the surface over much of the water body.

Depending on where you are, dangerously cold waters may be present much of the year. Alpine lakes can be very cold at any time, while ocean upwellings can cause cold waters along the NSW coastline even in mid summer.