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"It's freeeeezing cold!"
Law of Heat Conduction
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Dressing to stay warm is all about slowing the transfer of heat from your body to the outside.
This can be described quantitatively using the physical Law of Heat Conduction:
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| H = A k dT / dx |
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H is the amount of heat energy per time unit that moves from your body to the outside.
A is the surface area of your body.
dT is the difference in temperature between your body and the outside.
dx is the distance from your skin to the outside.
k is a constant determined by the insulating material.
The k, or thermal conductivity, of water is 0.6 and the thermal
conductivity of air is 0.023.
From this (0.6/0.023) you can see that the conductivity of heat through water is about 26 times greater than through air.
Dry fleece is mostly trapped air and has a thermal conductivity of
about 0.08 whilst cotton saturated in water is mostly water and will have a
thermal conductivity close to that of water.
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Strategies for Preserving Body Heat
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Above the water our body does not use much energy to regulate its temperature.
In the water we spend a considerable amount of energy to keep warm which leads to tiredness and dehydration.
We cool down about 26 times faster in water than in air.
Add windchill and you'll see the challenge.
For a more comfortable and ultimately safer swim follow these tips for conserving body heat:
- Stay warm before the swim. Heat loss is gradual and can start long before you get to the swim site.
- Reduce windchill.
Wear windproof outer layers to keep you warm.
Use unlined clothes as they won't get waterlogged if you enter the water.
- Stay warm between repetitive swims. Standing around in wet gear
between swims can add to your body's deprivation of warmth through
evaporative heat loss.
Windproof outer layers reduce this heat loss.
- You can develop hypothermia without immediately recognising it.
When choosing your swimming clothes, err on the side of thermal protection.
- Get warmed up as soon as possible after a swim.
You can start on the beach by toweling off and getting into dry clothes.
If you want to jump in again later have extra sets of dry clothes handy
as it is uncomfortable to put the wet and cold clothes back on.
- Become an educated consumer. Visit your local sports shop and have
them show you the different styles of protective garments and
accessories. Don't be afraid to ask questions.
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Cold Water
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Water doesn't have to be extremely cold to cause hypothermia.
Any water that is colder than body temperature causes heat loss.
Water that is colder than 20°C can quickly begin to cause hypothermia.
The following tips may increase your survival time in cold water, if you accidentally fall in:
- Wear a life jacket. If you plan to ride in a watercraft, wear a life jacket.
A life jacket can help you stay alive longer in cold water by allowing you to float without using energy and providing some insulation.
- Don't panic. If you're unable to swim to safety, stay calm. Unnecessary movements require you to exert extra energy and lose body heat.
- Don't remove your clothing. Buckle, button and zip up your clothes. Cover your head if you have a hood. The layer of water between your clothing and your body will be warmed and helps insulate you.
- Position your body to minimize heat loss. Use a body position known as the heat escape lessening position (HELP) to reduce heat loss while you wait for assistance. Hold your knees to your chest to protect the trunk of your body. If you're wearing a life jacket that turns your face down in this position, bring your legs tightly together, your arms to your sides and your head back.
- Huddle with others. If you've fallen into cold water with other people, keep warm by facing each other in a tight circle.
- Don't attempt to swim unless you're close to safety. Unless a boat, another person or a life jacket is close by, stay put. Swimming expends extra energy, lowers body temperature and can shorten survival time.
- Avoid excessive alcohol consumption and the use of illegal substances, because these may increase your risk of hypothermia. Also, don't drink alcohol and operate a boat or other watercraft. Alcohol can impair your ability to navigate the waters, increasing your risk of an accident and of falling into cold water.
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Windproof waterwear
keeps you warmer even when wet.
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Cold Weather
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Before you or your children step out into cold air, remember the advice that follows with the simple COLD acronym:
- C for cover. Wear a hat or hooded garment to prevent body heat from escaping from your head, face and neck. Cover your hands with mittens instead of gloves. Mittens are more effective than gloves are because mittens keep your fingers in closer contact with one another.
- O for overexertion. Avoid activities that would cause you to sweat a lot. The combination of wet clothing and cold weather can give you chills.
- L for layers. Wear loosefitting, layered, lightweight clothing. Outer clothing made of tightly woven, water-repellent material is best for wind protection. Wool, silk or polypropylene inner layers hold more body heat than cotton does.
- D for dry. Stay as dry as possible. In the winter, pay special attention to places where snow can enter, such as in loose mittens or snow boots.
During cold-weather months, keep emergency supplies in your car in case you get stranded. Supplies may include several blankets, matches, candles and some foodstuffs, such as granola bars or crackers. A cell phone also can come in handy. If your car is stuck in a snowbank, be careful about leaving the engine running, as infiltration of carbon monoxide inside the car may pose a silent danger.
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Practice Cold Water Swimming
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Sometimes it may be necessary to swim in clothes.
You may be on a sinking boat, or you are cut off by a rising flood or tide.
In most cases you simply want to cross a stretch of open water that is in your way
or you just fancy a swim outdoors.
Whatever may happen, you should practise and prepare for it.
- Reduce initial waterflow.
Before you enter the water tighten neck openings and cuffs.
This traps air for buoyancy and slows the water soaking your upper body.
Eventually the water will find its way in, but you can delay that.
How long the water takes to fully saturate your clothing depends on your movement in the water
and how watertight your oversuit is at neck, cuffs, waist and leg.
On short crossings that can make a difference.
- Enter the water carefully.
You can slow the water coming in if you move carefully.
Keep your clothes tight as long as you have buoyancy for airpockets.
You may notice that you float up higher than usual.
Eventually the water will seep in anyway.
- Let water flow out.
Once your clothing is fully saturated, loosen it a bit to allow the water to flow out so it doesn't collect anywhere.
The action of swimming tends to cause water to collect within your outer clothing, in sealed cuffs, sealed ankles or boots.
This somewhat restricts movement and slows you down.
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Keep warm clothes dry
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Cold water will rapidly cause fatigue.
Hypothermia will be a major factor to consider prior entering the water.
It may be worth removing relatively dry warm under suits prior to the swim and placing
them inside a waterproof bag for the duration of the swim.
If a fibre pile or fleece suit gets saturated it provides little or no thermal insulation.
Take it off and wring it out to expel as much water as possible before you put it back on.
This reduces the risk of subsequent hypothermia.
Hooded tops keep windchill off.
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