Traditionally, the temperature of the body was taken rectally using a long, low-reading thermometer (0–50°C was considered to be adequate). However, there are problems with using this site because any interference with the anus or rectum before a full forensic examination of the area in a good light may confuse or contaminate later investigations into the presence of biological materials such as semen, blood or hair.
The development of small electronic tempera- ture probes with rapid response times and digital
readouts has revolutionized the taking of body temperatures. These probes have allowed the use of other orifices, including the nose and ear, although it must be remembered that these areas are unlikely to register the same temperature as the deep rectum or the liver.
Currently, the most useful method of estimating the time of death is Henssge’s Nomogram (which is explained in some detail in Box 5.2). Crucially, the 95 per cent accuracy claimed for this method is, at best, only 2.8 hours on either side of the most likely time (a total spread of over 5.5 hours).
Henssge’s Nomogram relies on three measurements – body temperature, ambient temperature and body weight – and lack of accuracy in any one of these will degrade the final result. In addition, there is the application of empirical corrective factors to allow for clothing, air movement and/or water (Table 5.1) and it should be noted that application of these empirical factors can significantly lengthen the time spans that lie within the 95 per cent confidence limits.
The need to record the ambient temperature poses some problems because pathologists are seldom in a position to do this at the time of dis- covery and, as their arrival at the scene is often delayed by some tens of minutes or hours, it is most unlikely that the temperature at that time will still be of relevance. Therefore, the first police officers or scientists at the scene should be encouraged to take the ambient temperature adjacent to the body and to record the time that they made their meas- urement. This, however, may give rise to concerns about interpretation of physical findings (depend- ent on how and by what route the temperature is taken). An alteration of 5°C in the ambient tem- perature may lead to, at least, a 1-hour alteration in the most likely time of death.
Many pathologists have in the past used various
‘rules of thumb’ to calculate the time of death from the body temperature but these are generally so unreliable that they should not now be used.
Sometimes the perceived warmth of the body to touch is mentioned in court as an indicator of the time of death; this assessment is so unreliable as to be useless and is even more so if the patho logist is asked to comment upon the reported perceptions of another person.
Various other methods have been researched in as yet unsuccessful attempts to find the hands of the post-mortem clock. Biochemical methods,
Figure 5.12 Post-mortem animal predation. The wound margins of these rat bites are free from haemorrhage or reddening. Such injuries are commonly present around the eyes, ears and nose.
Estimation of the post-mortem inter val BOX 5.2 The rectal temperature–time of death relating nomogram
This nomogram is for ambient temperatures up to 25°C. Permissible variation of 95% (/h). The Henssge nomogram expresses the death-time (t) by:
Trectum Tambient
1.25 exp (Bt) .25 exp (5Bt) ; B 1.2815 (kg.625) .0284 37.2 Tambient
The nomogram is related to the chosen standard; that is, a naked body extended lying in still air. Cooling conditions differing from the chosen standard may be proportionally adjusted by corrective factors of the real body weight, giving the corrected body weight by which the death-time is to be read off. Factors above 1.0 may correct thermal isolation conditions and factors below 1.0 may correct conditions accelerating the heat loss of a body.
(Continued)
10 10
10 10 10 10 10 10 10 10 10 10 10 10 10 10 10
8 8 8 8 8 8 8 8 8 8 8
7 6 6 6 6
6 6 6 6 6 6 6 6 6 6 6 5 5
3 3
2 2 2 2 2 2 2 2 2 2 2 2 2 2 2
1 1 1
5 5
4 4 4
4 4 4 4 4 4 4
12 12 12 12 12 12 12 12 12 12 12
14 14 14 14 14 14 14
14 14 14 15 15
16 16 16 16 16 16 16
16 16
18 18 18 18 18 18 18
18
20 20 20 20 20 20 20
20 20 20
20 22
22 22 22 22 22 22
32
24 24 24 24 24 24
24 24 24
26 26 26 26 26
28 28
28
28 28 28
30 30 30
34 40
31 33
38 44
36 36
32 34
15 20 16
18
25 25
25
30 30
30 30
35 35
35 35
35
4040 40
40 40
40 40 40 40 42
48
46
50 50 50
50 50
50 50 50
56 52
60 60
60 60
60 60 60
70 70 70 75 65 65
55 55
45 55 45 45
45
70 7080
80 80
80
30
10 10
0 5 10 10 20 25 30 35
15 20 30 40 50 60 70 80
90 100110
120
140160180200 2,8
4,5
7,0 4,5 3,2 2,8
°C
°C
15 KILOGRAM
20 3040
5060 7080
90100 110120
140160 180
200 Usingcorrective factors
Standard(naked–still air)
20 15 10 5 0 5
10 A M B I E N T
R E C T U M
5 The appear ance of the b o dy after death
BOX 5.2 continued
How to read off the time of death
1.Connect the points of the scales by a straight line according to the rectal and the ambient temperature. It crosses the diagonal of the nomogram at a special point.
2.Draw a second straight line going through the centre of the circle, below left of the nomogram, and the intersection of the fi rst line and the diagonal.
The second line crosses the semicircle of the body weight and the time of death can be read off. The second line touches a segment of the outermost semicircle. Here can be seen the permissible variation of 95%.
Example: temperature of the rectum 26.4°C; ambient temperature 12°C; body weight 90 kg.
Result: time of death 16 1.8 hours. Statement: the death occurred within 13.2 hours and 18.8 hours (13 hours and 19 hours) before the time of measurement (with a reliability of 95%).
Note: If the values of the ambient temperature and/or the body weight are called into question, repeat the procedure with other values which might be possible (see Table 5.1 for ‘corrective factors’). The range of death-time can be seen in this way.
Requirements for use
● No strong radiation (e.g. sun, heater, cooling system).
● No strong fever or general hypothermia.
● No uncertaina severe changes of the cooling conditions during the period between the time of death and examination (e.g. the place of death must be the same as where the body was found).
● No high thermal conductivity of the surface beneath the bodyb. Notes
aKnown changes can be taken into account: a change of the ambient temperature can often be evaluated (e.g. contact the weather station); use the mean ambient temperature of the period in question. Changes by the operations of the investigators (e.g. taking any cover off) since fi nding the body are negligible: take the conditions before into account.
bMeasure the temperature of the surface beneath the body too. If there is a signifi cant difference between the temperature of the air and the surface temperature, use the mean.
This representation of the nomogram should not be used for actual cases
Table 5.1 Empirical corrective factors of body weight
Dry
clothing/covering
In air Corrective factor Wet-through clothing/covering wet body surface
In air/water
3.5 Naked Flowing
0.5 Naked Still
0.7 Naked Moving
0.7 1–2 thin layers Moving
Naked Moving 0.75
1–2 thin layers Moving 0.9 2 or more thicker Moving
Naked Still 1.0
1–2 thin layers Still 1.1 2 thicker layers Still
2–3 thin layers 1.2 More than 2 thicker layers Still
1–2 thicker layers Moving or still 1.2
3–4 thin layers 1.3
More thin/thicker layers Without infl uence 1.45 Thick bedspread +
clothing
1.8
Combined 2.4
For the selection of the corrective factor of any case, only the clothing or covering of the lower trunk is relevant! Personal experience is needed, nevertheless this is quickly achieved by the consistent use of the method.
F urther information sourc es
including vitreous humour potassium levels and changes in enzyme and electrolyte levels else- where in the body, have been researched; some remain as interesting research tools but none has been successful in routine work.