Those alcohol limits
I have just read the Star Letter in the July edition of Pilot and as both a Forensic Toxicologist and a PPL I was aware of the lower limit, however I wish to correct your correspondent’s units for alcohol in blood. The correct figure for the legal limit in blood for transport workers is 20 as your correspondent states but the concentration should be milligrams per 100 millilitres of blood and not micrograms per 100 millilitres of blood. In shorthand the limit is written as 20 mg% where mg = milligrams not micrograms. The blood alcohol limit for drivers in England and Wales is 80 mg% as stated, but this blood alcohol concentration is associated with a significant increase in the risk of accident, hence the lower limit of 50 mg% for Scotland and indeed many other countries, and 20 mg% for Transport workers including pilots.
In the UK the agreed ‘average’ elimination rate used by the forensic community is 19 mg% per hour but this linear blood alcohol elimination rate only applies until the concentration declines to 20 mg%. Below 20 mg% the elimination rate decreases as the concentration decreases and the elimination kinetics revert to the normal first-order.
The eight hour bottle to throttle is simplistic but easy to remember! If one has a heavy drinking session it may take well over twelve hours to be legal to drive but I suspect not legal to fly. And the hangover following heavy drinking would not be conducive to the safe operation of complex machinery. Eight hours would be fine after a couple of drinks for most people.
Of course there may be interactions between alcohol and many medicines so if in doubt about fitness to fly one should err on the side of caution and drink carefully or not at all, or consult your AME for advice.
We received a number of letters pointing out this error; thanks to our eagle-eyed readers! — Ed