The length of time a body remains warm after death depends on several factors. In general, a dead body starts cooling down immediately after death, until it reaches ambient temperature. How long this takes can vary greatly, but we’ll go over the key factors that determine the rate of cooling.
Core Body Temperature at Time of Death
A living human’s core body temperature is around 98.6°F (37°C). At the moment of death, this starts to drop as the heart stops beating and blood circulation halts. The warmer the body was at time of death, the longer it will take to cool down to ambient temperature.
For example, someone who died of an infection with high fever would cool more slowly than someone who died from blood loss or trauma. Environmental temperature also plays a role here – a body cooling in a hot environment will take longer to drop to ambient temperature than one in a cold environment.
Cause of Death
How someone died can significantly affect the rate of cooling. Deaths due to trauma, blood loss, or asphyxiation cause the body to cool faster than “quiet” deaths from illness or organ failure. This is because traumatic deaths involve a greater loss of blood circulation before the heart stops.
A body that has bled out will cool down more rapidly, as there is less blood circulating to transfer core body heat to the extremities. Similarly, asphyxiation limits oxygen to organs and cools the body more quickly. In quiet deaths from heart failure or respiratory diseases, the blood remains warmer and body temperature drops more gradually.
Body Type and Size
A person’s body type and size impacts the rate of cooling. Bodies with more fat and insulation cool more slowly than slender bodies with less fat. Muscle also cools more slowly than fat.
Larger bodies retain heat longer than smaller bodies due to basic thermodynamics – more mass retains more heat energy. Children and infants, with their smaller bodies and greater surface area to mass ratio, tend to cool down faster than adult bodies.
External Conditions
The environment the body is in markedly affects cooling. Air temperature, humidity, wind, and exposure to water all determine how fast heat is lost. Bodies cool fastest when exposed to cold, dry conditions with wind or air circulation.
Water draws heat away from bodies much more quickly than air. A body that is submerged in water after death will cool significantly faster than one exposed just to air. Cool, dry ground or a metal surface will also draw heat away faster than warm, damp air.
Clothing and Coverings
What garments or coverings are on the deceased person also impacts the cooling rate. Clothing helps insulate the body and slow heat loss, while nudity or wet garments accelerate cooling.
A body wrapped in sheets or blankets will retain warmth longer than one left uncovered. Autopsies and embalming procedures can also speed cooling by exposing internal organs to ambient temperatures.
Cooling Rate Timeline
Given all these variable factors, estimating time since death from body temperature can be complex. However, some general timelines exist:
- In the first hour after death, the body cools about 1.5°F (0.83°C)
- In the first 2 hours, it cools about 3°F (1.67°C)
- The body loses up to 90% of its heat in the first 24 hours after death
- Within 16-20 hours, the body will usually reach ambient temperature
- Brain and internal organs cool faster than external parts of the body
- An obese body with insulation may take 1-2 days to cool to ambient temperature
The table below shows approximate cooling rates under different conditions:
| Conditions | Hours to Reach Ambient Temperature |
|---|---|
| Nude body in still air at 70°F (21°C) | 15-18 hours |
| Nude body in moving air at 70°F (21°C) | 8-12 hours |
| Body in water at 70°F (21°C) | 4-6 hours |
| Body in loose clothing at 70°F (21°C) | 20+ hours |
| Obese body at 70°F (21°C) | 36-40 hours |
Measuring Body Temperature
When estimating time since death, investigators take temperature readings from several parts of the body:
- Rectum – most accurate reading of core body temperature
- Liver – cools slower than surface skin
- Muscles
- Skin
Rectal temperature drops slowly, while skin temperature declines rapidly. Measuring different sites gives a more complete cooling profile than a single reading and allows a better estimate of when death occurred.
Algor Mortis
“Algor mortis” refers to the natural cooling of a body after death. Investigators use cooling formulas and algor mortis body temperature to back-calculate an estimated time of death – even days or weeks after a body is discovered.
However, various environmental factors can alter natural cooling rates, making time of death estimates inexact. Overall cooling patterns give a reasonable framework, but are most accurate in controlled conditions near the time of death.
Influence of Cold Temperatures
In very cold conditions, a body may actually drop below ambient temperature and freeze. Once freezing occurs, the body temperature plateaus until thawing again. This can greatly alter cooling patterns.
A body found frozen shows little cooling after death occurred, as the freezing halted temperature decline. Caution must be used in estimating time since death under these circumstances, as cooling formulas do not apply well to frozen bodies.
Importance of Scene Conditions
Investigators must consider the conditions a body has been in when interpreting algor mortis temperature. Was the scene temperature warm, cold, wet, or dry? Was there shade, wind, rain, or blowing air?
Observing the scene helps determine which environment factors were present to properly apply cooling rates and estimate time since death. If the body was moved or conditions changed, it becomes far more challenging to get an accurate post-mortem interval.
Role of Clothing and Wrappings
Clothing and any coverings or wrappings on a body significantly alters cooling rates. Investigators should catalog clothing or wrappings on the body and their insulating capacities.
For example, a nude body would cool faster than one wearing multiple layers of clothing. Meticulous documentation allows more precise adjustments to be made in algor mortis cooling formulas.
Variation Between Body Sites
Different parts of the body cool at different rates. The brain and organs in the torso stay warmer longer than the extremities. Areas covered by clothing or touching the ground cool slower.
Taking temperature readings at different body sites provides a bigger picture of the overall cooling process. The most accurate time since death estimate analyzes data from all major body areas.
Role of Body Fat
Corpses with excess body fat require more time to cool to ambient temperature. Fat insulation continues slowly releasing heat from the body’s core over an extended time. Obese bodies can take 1-2 days to reach ambient levels.
Conversely, emaciated bodies or those with very low fat cool much quicker. Low fat provides less insulation to retain heat, allowing faster cooling to match ambient conditions.
Impact of Embalming
If a body has been embalmed before temperature readings are taken, time of death estimates become far less accurate. Embalming drains body fluids and replaces them with cold embalming chemicals.
This disrupts natural cooling patterns, dropping temperatures faster than normal. Bodies embalmed soon after death are the most difficult to assess for time since death based on temperature methods.
Estimating Time of Death
While inherently inexact, investigators can provide reasonable estimates of time since death based on algor mortis body cooling:
- Measure ambient temperature of the scene
- Take rectal, liver, muscle, and skin temperature readings
- Factor in body type/fat, clothing, environmental conditions
- Input data into accepted cooling formulas
- Derive an estimated post-mortem interval range
Cooling formulas provide a starting point, which forensic evidence can further confirm. Crime scene clues also help narrow down probable time frames.
Length of Time Body is Warm
A general rule of thumb is that a dead body loses around 90% of its heat in the first 24 hours. However, a “warm” feel is subjective and depends on comparing body and ambient temperatures.
In cold conditions, a body may feel warm to the touch 12 hours or more after death, as it retains core body heat longer than the environment. In hot conditions, it may feel room temperature much sooner.
Touch alone is not very reliable in gauging time since death. Temperature readings provide more objective data to estimate when a decedent passed away.
Variation Between Bodies
Every deceased individual cools at a slightly different rate according to the factors discussed. There is no universal formula where X hours always equals X degrees of cooling.
General guidelines provide starting points for investigators to interpret algor mortis patterns. The unique circumstances of each death modifies these approximations to varying degrees.
Careful analysis and reasonable interpretations must be made when estimating time since death based on body temperature.
Errors in Temperature Measurement
Several potential errors can creep into assessing body temperatures if proper procedures are not followed:
- Allowing too much time to elapse before taking readings
- Improper thermometer placement or technique
- Failure to measure ambient temperature
- Incorrect thermometer calibration
- Recording or conversion errors with readings
Meticulous methods and tracking of data lessen these sources of mistake. Cross-checking readings and instrumentation improves the reliability of results.
Conclusion
A dead body starts cooling right after death, until it equilibrates with the temperature of the environment. Many factors affect the rate of heat loss and how long a body remains warm. In average conditions, a body becomes ambient temperature 16-20 hours after death.
Forensic investigators use body temperature readings at the scene along with cooling formulas to estimate a post-mortem interval. However, many variables can alter natural cooling patterns, making time of death assessments an inexact process with a range of error.
Precise documentation and careful interpretation allows investigators to provide reasonable timeframes for when death likely occurred.