The determination of blood ethanol concentration in a deceased
pilot is an important part of the accident investigation. The
finding of an elevated blood alcohol level in such a case may have
significant implications, both medico-legal and social. It is
therefore important to ensure that the finding of an elevated blood
alcohol concentration is valid.
It is known that micro-organisms involved in the process of
putrefaction after death can produce alcohol, usually a mixture of
ethanol and other volatile substances. This process occurs when a
body is not refrigerated soon after death and is hastened by
environmental conditions such as high temperatures and when the
body has been traumatised.
Older methods of analysis could not distinguish between ethanol
and mixtures of other volatile compounds. Current methodology (gas
chromatography) can isolate ethanol and identify other
substances.
There is a range of specimens in which ethanol can be measured.
Their suitability for analysis can be determined by microbiological
studies although this would not be routinely performed in most
laboratories.
Medico-legal and forensic implications are associated with a
'blood alcohol concentration'.49 It therefore seems most useful to
measure the ethanol level in a specimen of blood, but this may not
always be available depending on the state of the body. Vitreous is
the next specimen of choice, and valid conclusions regarding the
ingestion of alcohol can usually be made based on the results of
its analysis.
Urine analysis may also be helpful, particularly in conjunction
with blood and vitreous. Comparison of levels of these three
specimens is probably the ideal means of interpreting blood alcohol
concentrations. If none of these specimens is available, resort can
be made to other organ and tissue samples but there are
difficulties in both methodology and interpretation of results
relating any alcohol present to ingested ethanol.
Ethanol in gastric contents generally indicates recent
ingestion, but the rapid absorption of ethanol and post-mortem
diffusion from the stomach may limit the usefulness of analysis of
gastric contents.
The presence of volatile compounds in addition to ethanol (seen
by gas chromatography methods) may suggest post-mortem production
by micro-organisms but also needs to be interpreted cautiously.
It is possible to measure parameters which are associated with
or indicate ethanol consumption. These are qualitative only and do
not enable the blood ethanol concentration to be calculated or
estimated. They have applications in a clinical setting where they
address the issue of alcohol consumption in previous days. This is
not usually the main issue in a fatal aviation accident
investigation, where the "bottle to throttle" rule applies, and the
issue is what factors were influencing the pilot's capacity to fly
the aircraft. Two of these measurements, ethyl glucuronide and the
5-HTOL: 5-HIAA may have some application in the future of fatal
aviation accident investigation but they are not currently
performed routinely.