Jose commented on the UK CAA GASIL article on blood alcohol:

>>
The human body manufactures its own alcohol, and it is possible for the
level
of that self-manufactured' alcohol to almost reach that 20 milligram level,
so it would be prudent for anyone who is subject to the Act to think of the
permitted level as equating to no consumed alcohol at all.
<<

> Has any of you heard of such a thing? How does the 20 milligram level
compare
> with blood alcohol measurements in the US?

The UK driving limit is 80 mg/dl. The US driving limit is, I believe, 100
mg/dl in most states.

For flying the FAA limit in 91.17 is .04 percent by weight, i.e. approx 40
mg/dl. The proposed UK limit is 20 mg/dl.

A bit of Medline searching reveals a couple of articles

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10976182&dopt=Abstract

http://alcalc.oupjournals.org/cgi/content/full/36/6/608

showing that the endogenous concentration is approximately 0.04+/-0.04
mg/dl, in other words one thousandth of the FAA limit, on average.
Extraordinary cases have been reported, usually when atypical individuals
(with very serious yeast infections) had eaten carbohydrate-rich foods.
These people probably shouldn't be flying!

Julian Scarfe