Those al­co­hol lim­its

Pilot - - FLIGHT TEST - Alex Al­lan PHD, New­bury

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

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