*** Floating of the Drowned Human Body  ***

From:	 JELSAR@aol.com
Sent:	 Monday, June 29, 1998 8:35 PM
To:	 sar-l@listserv.islandnet.com
Subject: Re: water search

John Stankiewicz asks "In several drowning recoveries involving accidental
drowning while swimming, suicides, and other somewhat *normal* drowning
events, the bodies do not float for days or even weeks. Yet in several
flash flood incidents, I have noted that the bodies surface within hours
of being swept into the river. Can anyone explain this phenomenon?"

There are several contributing physical factors facilitating the early
discovery of bodies caught in flash floods or other swiftwater accidents.  

1) the bodies get caught just like other debris in certain "log-jam" areas
in the eddy currents. It is pretty easy to figure out where to look for
bodies, so searchers are less dependent on waiting for the gases of
decomposition to float up the victims to the water surface.

2)  the velocity of water and water-borne objects at the air-water surface
is faster than the velocity of water and water-born objects at the
ground-water interface. The drag coefficient is higher along the bottom as
well, creating a turbulent flow with vectors radiating outwards away from
the bottom. Even solid materials will be propelled towards the air-water
surface if the stream velocity is fast enough. Where an object "layers"
out in the stream will depend on the velocity of the stream, the
characteristics (laminar versus turbulent) of the current, and the mass
and density of the object. When the stream comes to a log-jam area
(produced by the eddy currents and change in direction/velocity of the
current), the body is more likely to be carried near the air-water
surface, and is therefore more likely to be caught or washed up in a
visible location.

3)  The density of the human body (and whether or not it floats in water)
is dependent on the ratios of fat and gas components relative to the
amount of muscle, bone, and gristle in the body. Gases can be trapped in
lungs, intestinal tracts, sinuses, mastoid air cells, and in clothing.
If the submersion death takes place quickly enough, these trapped gases
won't have time to diffuse out, so the bodies from flash floods will tend
to have more bouyancy. The bodies of children, women, and obese
individuals tend to have greater bouyancy as a baseline.

4) Additionally, as many as 20% of submersion victims have little or no
water in their lungs when autopsied, even if they have passively drowned
(as in a swimming pool). In order to get water in the lungs (to displace
the gases), the victim has to be breathing with his or her head underwater.
The flash flood victim may not be breathing at the time of death: trauma
like a head injury could have stopped the act of breathing, or the heart
could have stopped while the victim was still holding his breath, or the
vocal cords could have gone into spasm when they encountered the first
breath of water. There is a fairly high probability in the flash flood
situation that there will be significant amounts of air left in the lungs
at the time of death, and that air will contribute to the body's overall
bouyancy.

Hope this is helpful. Thanks for asking the question! It is not often I
can combine my engineering background with my river running interests to
answer a question on a SAR list.

Josh Ellis
chemical engineer
roving consultant, currently in Florida