body makes its own blood alcohol?

ref:
http://www.caa.co.uk/docs/33/srg_gad_gasil4of2003.pdf

On the middle of page 3 of the document it states:


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. It may be worth
pointing out to those planning on flying abroad that other states may have an
even lower limit.


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

Jose

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