Cold water
Cold water
The seawater alongside the Dutch coast normally will not get warmer than 21 ° C. During the springtime the weather is getting better and sometimes it is
better as during the summer season. In this period the water is
cold and can be lower than 16 °C. Many inpatient people however want to take a swim. However the temperature can be so low that hypothermia can occur. If this happens when you are caught in a rip the consequences can be very serious. Cold water causes hypothermia; beside this the viscosity is worse compared to warmer water. The following information is copied from the website of the Dutch information for swimming.
Zweminformatie Documentatie Centrum (click here for the Dutch article).
Different theories developed by experience indicate the effects and times some-one can stay in cold water before a life threaten situation is rising, see article.
Introduction
There is a lot of water in the Netherlands. The possibility to get into the water unwanted is quite big. The temperature of the outer water in winter is about 40 C during winter and about 200 C during summer. If people get unexpected into the water they may lose a lot of their body-heat. If the inner-temperature falls below 350C we talk about hypothermia. Hypothermia can occur at swimmers, diver’s fisherman, surfers and all kind of people dropping into the water. The human body is fighting against this cooling down by producing more heat by increasing the circulation of the metabolism and starting to shiver.
Cooling down symptoms
|
Body temperature |
Symptoms |
|
370C |
Metabolism is speeding up |
|
350C |
Disorientation, heart rate is lowering, confusion |
|
330C |
Muscle stiffness, big pupils, confusion, shivering stopped, disoriented talking, spasms. |
|
310C |
No muscle reflexes, victim can become unconscious by to less oxygen |
|
290C |
Unconscious, no heart beat, no reaction on pain. Every unconscious person with possible hypothermia should be reanimated and warmed up on a proper way. The border between life and death is reached |
|
270C |
Death, no reanimation is possible anymore. Only doctors can conclude if reanimation is not necessary anymore. |
Survival times.
Roughly the time a person may survive is as follows:
|
Water temperature |
Approximate survival time in water |
|
00 C |
9 minutes |
|
50 C |
1 hour |
|
100 C |
1 hour 45 minutes |
|
150 C |
6 hours 30 minutes |
|
200 C |
30 hours |
|
250 C |
4 days or longer |
The survival time is depending on more aspects like the shape of the body, if you used alcohol or medicines, clothing and overall physical condition.
Temperature effects
The next graph shows the relation between moving in the water for 20 minutes and the difference between clothing and no clothing. The left axe is showing the body temperature.
Stilliggend means no movement. Gekleed is clothing on. Bewegend is moving and ontkleed is no clothing on.
Formula to calculate the survival time
Scientist did investigate the time someone has until the body temperature is lowering to 300 C.
The formula is for a non moving person with clothing and a rescue belt on.
Survival time in minutes =15+7.2/(0.0785-(0.0034xwatertemp in 0 C))
At a water temperature of 120 C the survival time will be 206 minutes.
In general the following table shows more facts:
Change of survive
Roughly the time a person may survive is as follows:
|
water temperature |
wetsuit |
dressed |
naked |
|
5° C |
3 hour |
1 hour |
½ hour |
|
10° C |
9 hour |
3 hour |
1 hour |
|
15° C |
12 hour |
5 hour |
2 hour |
|
20° C |
15 hour |
8 hour |
4 hour |
Windchill
Windchill-can also influence our body temperature by a combination of wind speed and air temperature. This is called windchill. This is common amongst such as windsurfers and sailors. The windchill is the cold that we really feel. However for people swimming there is no windchill effect
Viscosity of the water
This factor is not negligible for our swim performance. Viscosity is a measure of the thickness of the fluidity (toughness) of liquids such as the basin water. From experience, everyone knows that oil or syrup at elevated temperature is a thin liquid, so a smaller viscosity. This is the same with water. The table below indicates the viscosity of water at any water temperature:
|
Watertemperature |
|
Viscosity (in centipoises) |
|
10° C |
= |
1,30 |
|
15° C |
= |
1,14 |
|
20° C |
= |
1,00 |
|
25° C |
= |
0,89 |
The table shows the non-negligible differences ± 40%. The resistance in the water is approximately proportional to the viscosity. So it will cost us approximately 40% more effort to swim a certain distance in water of 10 degrees Celsius compared to go the same distance in water of 25 degrees Celsius.
Heat dissipation of humans
The water temperature has effects on the temperature regulation of the swimmer. The heat dissipation in the water shall be done largely by conduction and flow. The body of each swimmer works as a "water-cooled" engine. In the water the heat dissipation is 3 to 4 times greater than on the countryside because the conductivity of water is 20 times better than air. The body is preventing cooling down by:
● blood vessel constriction in the skin, causing the heat dissipation limited;
● increase the heat production by increase in metabolic rate and, if necessary, the involuntarily shivering or shaking. This requires additional power of heart and blood vessels, in addition to the power needed by the physical activities in the water.
Why cools the one person faster than the other?
The above also explains that swimmers with a thick subcutaneous fat layer cool down slower than skinny fast swimmers. Girls can generally remain longer in the water than boys by their higher fat content. Children cool faster than adults since the size of the skin surface is important in all forms of heat dissipation. In this context, we compare two cubes, one with an edge of 1 centimeter and one with a shape of 10 cm.
| "Child" | "Adult" | ||||
 1cm |
10cm |
 |
|||
| Surface: 6 x 1 = 6 cm2 Content: 1 cm3 |
Surface: 6 x 100 = 600 cm2 Content: 1000 cm3 |
||||
At the small object (child) is the ratio surface/content = 6 to 1 and in the large object (adult) surface area the surface/content ratio is 600 to 1000. The child has in relation to its volume a relatively larger surface area than an adult. Surface increases with the 2nd power, volume with the 3rd power. This means that the skin that regulates the heat dissipation, at children faster losses heat to the water than an adult. Children lose fast heat, they have the quick cold.
● Children under 3 years: loss per 15 mins in water of 31 0C, depending on motion activity and supplied energy to 0.2 0 C of body heat.
● Children from 3 to 6 years: the loss per 15 minutes 0.1 0C. This means that the body temperature per lesson of 45 minutes decreases 0.3 0C at children between 3 and 6 years.
● Children under 3 years: lose so in such a les 0.6 0C of body temperature in water of 31 0C .
When body temperature lowers 0.7 0C below the 36.6 0C, then the human organism becomes particularly susceptible to infections because the resistance reduces. Never let small children wait during exercises in the pool stay wet on the side, after they have been in the water, or be showered.
The ideal water temperature
At a water temperature higher than 32 0C a swimmer cannot get rid of his surplus of heat. The body temperature goes up. At a water temperature of 29 a 30 degrees Celsius skinny people can maintain without much effort their body temperature. The ideal water temperature is 28 a 29 0C. The opinion of a reasonable water temperature is 10 degrees Celsius below body temperature, so 27 0C. Intensive training may slightly lower temperature. By babies, toddlers, children, the elderly, invalids and rheumatism patients the temperature might be better a slightly higher than the ideal temperature:
Disabled and elderly people, because they often are less active and small children because they also have a relatively large skin surface.
To learn more about hypothermia see the information supplied by the Royal Dutch Life Organization.
