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Overview :
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.
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