In studying the Dylan Redwine case, where much attention is right now focused upon Vallecito Lake as a possible site where he may be found, I have learned many things about this subject.
First, regardless of whether or not someone drowns, or if they are deceased upon entering the water, their body will sink (unless any possible air trapped in clothing is enough to retain buoyancy of the body, but that is
if the person is wearing clothing that is capable of actually trapping air. A nude body, for instance would sink immediately).
When someone drowns their lungs fill with water, and the body sinks. When someone is already deceased, they have no air in their lungs that would create buoyancy at that point - the lungs deflate (hence what people refer to as the
"death rattle"* or "giving up the ghost" that is the sound heard just after a person takes their last breath). So, I'm not sure who told you that air is trapped in the lungs after death, but that would definitely not be accurate.
How long the body will remain under water before surfacing has mostly to do with the temperature of the body of water itself. A body floating to the surface does so because of putrefaction (gases and such that occur as a result of the chemical changes caused by decomposition). When these gases reach a point within the body it then becomes *lighter* than the water, so to speak, and then the body floats up to the surface.
In warm water that may take as little as 3 days. In very cold water, it could take many weeks before decomposition really even sets in due to the temperature slowing down bacterial growth a lot.
Another factor in regard to a body floating would be whether or not the body was weighted down, or whether or not there are trees and branches at the bottom of the body of water in which a body may be stuck on... Either of those things being present would presumably allow even a body in warmer water to stay submerged longer... Won't get into detail on that part as it's rather gory at that point.
Excerpt:
In summary - whether a person is alive and drowns, or a person's body is deposited into a body of water, they will sink to the bottom. A corpse will always maintain a position of head-down lower than the rest of the body at the neck. This is similar to the "dead man's float" taught in swimming classes, although this positioning is also maintained below the surface. If the body is moved along by a current this will be evidenced by post-mortem injuries to the top/front portion of the head as that is what will come into contact with any debris on the bed of the lake, creek, or river...
How long a person's body will remain submerged in the water does not depend on if they drowned, or if they were deceased. The biggest factor is the temperature of the water as it relates to the rate of putrefaction of the body. Cold water can delay this process very significantly (as can be seen by the estimates of bodies floating up in the Thames River at different times of the year, and the fact that oceans and the Great Lakes many times never "give up their dead" due to the extreme cold temperatures found at the bottom).
Thus, it is not a matter of "if" a body will sink or not, but rather how long it will be until said body will rise to the surface and float.
dlink: I'm sure your pathologist friend may have just given you the short quick explanation. Yes, all bodies in water will float, eventually. However, they will not float immediately unless a considerable amount of air is trapped in clothing, and in the absence of trapped air in the clothing they will never float before they have sunk to the bottom and the decomposition process and putrefaction reaches the stage where the gases are of such a volume as to make the body buoyant enough to rise to the surface again.
There is a lot more information on this subject available at the link above - I only excerpted a very small portion at the very end of the document. There is much documented evidence for what is explained in this post.
As always, all of the above is MOO, (unless there is a link cited to back-up my claims)! :cow:
ETA:
CORRECTION: * The death rattle isn't actually when the lungs relax and let out all of the air. It's actually the sound of saliva in the throat that occurs shortly before death. My apologies for that mistake. Regardless, immediately after death the muscles completely relax, and any remaining air would be expelled. (I'm looking for a specific link to back this up, though - just for good measure.)
ETA:
dlink - I don't know how to ask this without sounding rude... Are you sure you got your information from a friend who is a pathologist, and not from information in a Yahoo! Answer article that references a mailbag answer on the Straight Dope website which discusses Huckleberry Finn, and if someone hit with a cannon would float in the water???
The reason I as is because I found the exact wording you used in your post here:
http://answers.yahoo.com/question/index?qid=1006020700794
which referenced -
http://www.straightdope.com/columns...n-cause-a-drowned-body-to-rise-to-the-surface
BBM
Why wouldn't you just link to the information instead of copying it, and then not citing where you got the information from? This is a word-for-word quote, and not information you got from a "pathologist friend", is it? It's not really helpful to forward information not based upon scientific facts. And particularly when the information is word for word from Yahoo! answers and a forum discussing a novel...
