While we’re alive our body temperatures are determined by metabolism. It’s a different ballgame, though, once the bucket is kicked.
After death, the body’s core temperature remains fairly constant for a couple of hours. Then it begins to cool by radiation, conduction, and convection, at a rate of 1.5 degrees per hour, until it reaches the ambient temperature—20-30 hours later.
However, investigators shouldn’t use the body temperature as the sole means of determining when a victim died. There are factors that could, and do, alter the natural cooling process.
When the “moment” arrives and the victim succumbs to wounds, illness, or natural death, there are elements that may affect the cooling rate of the body, such as:
- Ventilation: A room that’s well-ventilated could actually speed up the rate of cooling by increasing the rate of evaporation.
- Humidity: A body in a humid location cools at a slower rate than one in a hot, dry climate.
- Insulation: A body that’s wrapped in something (including excess body fat) cools slower than one that’s left out in the open.
- Surface temperature: A body lying on a hot surface will cool at a slower rate than one that’s found lying on a cold surface.
And, of course, a body in a hot environment cools much slower than one found lying in a in the snow, or a vat of ice cubes.
There are also factors that come into play that could alter the body temps even before death occurs, such as:
- Consumption of drugs, extreme physical activity, and fever could all increase the body temperature.
- Hypothermia could lower the body temperature.
These factors would change the length of time it takes a body to reach the surrounding air temperature.
Finally, the rate of cooling also affects other “after death” processes, such as rigor mortis—heat speeds up rigor and cold slows it down.
By the way, other factors may also speed up rigor, such as extremely violent exertion prior to death, and alkaloid poisoning. Factors that could slow the rigor process are hemorrhaging by exsanguination, and arsenic poisoning, to name a couple.
And … a handy rule of thumb for decomposition:
One week in air = two weeks in water = eight weeks under ground.