MadSci Network: General Biology

Re: How long can a human float in water?

Date: Fri Sep 26 03:03:50 2003
Posted By: Will Higgs, Research Associate
Area of science: General Biology
ID: 1063753517.Gb


I cannot think of any reason why a person who starts off floating should 
sink later.  It is like asking 'How long can a ship float in water ?'

The buoyancy of a human - or a ship - would only change if there was some 
change in the density of the floating object.  If the density of the human 
is less than that of water (0ne gramme per cubic centimetre) then they 
will continue to float so long as they are alive.  

Even if the person drank a lot of water, this should not affect their 
buoyancy, as the water consumed would be of the same density as the water 
they were floating in.  If, however, as tends to happen to people floating 
in rough water for a long time, they were to inhale more and more water, 
then that inhaled water would fill up the air space in their lungs and 
make them more likely to sink.

Apart from the air space in our lungs, the other factor which helps us to 
float is the amount of fat in our bodies.  Women have, on average, a 
higher proportion of fat in their bodies so that a drowning woman would 
probably float for longer than a drowning man.

To that happy thought I can only add that the behaviour of bodies after 
they have stopped breathing is much more interesting - but you did specify 
that they had to be alive !

Hope this helps your research.


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