The method of Fiddes and Patten for estimating the time of death uses rectal and environmental temperatures. It uses the virtual cooling time, which is the time it takes a body to reach a 15% difference between rectal and environmental temperatures.
Variables:
(1) rectal temperature in °C at the time of death (normally 37°C)
(2) rectal temperature in °C at time 1
(3) rectal temperature in °C at time 2
(4) time interval in hours between time 1 and time 2
(5) environmental temperature in °C at time of death
percent fall in rectal temperature at time 1 =
= ((rectal temperature in °C at time of death) - (rectal temperature at time 1)) / ((rectal temperature in °C at time of death) - (environmental temperature in °C))
percent fall in rectal temperature at time 2 =
= ((rectal temperature in °C at time of death) - (rectal temperature at time 2)) / ((rectal temperature in °C at time of death) - (environmental temperature in °C))
Estimating Percent of Virtual Cooling Time from
Percent Fall in Temperature Difference
The percent fall in rectal temperature correlates with the percent fall in the virtual cooling time in a semilogarithmic manner (fall in temperature semilogarithmic, percent virtual cooling time linear). Using data in Hennsge (1995, Figure 2.22 page 36), the fall in temperature difference and virtual cooling time can be approximated by equations from JMP:
For percent fall in temperature from 0 to 30 percent,
percent of virtual cooling time =
= (0.00375 * ((percent fall in temperature) ^ 2)) + (0.5825 * (percent fall in temperature)) + 0.075
For percent fall in temperature from 30 to 60 percent,
percent of virtual cooling time =
= (0.005 * ((percent fall in temperature) ^ 2)) + (0.49 * (percent fall in temperature)) + 1.7
For percent fall in temperature from 60 to 85 percent,
percent of virtual cooling time =
= (0.0546231 * ((percent fall in temperature) ^ 2)) - (5.972111 * (percent fall in temperature)) + 211.30905
These are calculated for the percent fall in temperature seen at time 1 and time 2.
Estimating the Time Since Death
difference in percent virtual cooling time between time 1 and time 2 =
= (percent of virtual cooling time at time 2) - (percent of virtual cooling time at time 1)
100% of virtual cooling time in hours =
= (time interval in hours between time 1 and time 2) * 100 / (difference in percent virtual cooling time between time 1 and time 2)
time since death in hours =
= (100% of virtual cooling time in hours) * (percent fall in rectal temperature at time 1)
Limitations:
• The precise rectal temperature at the time of death may not be 37°C. The more that the actual rectal temperature deviates from this value then the more inaccurate the estimates.
• The environmental temperature needs to be relatively constant for the method to provide meaningful estimates.
