I'm afraid I see no harm in it at-all. I found out about the new 20%mg limit a while ago and having a few hours to spare, did some research in the RAeS library in London. Below are my findings (I have posted them before, but not in this forum).
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The basic unit of alcohol within the body is mg/100ml of blood (referred to as %mg BAL). Obviously the relationship between how much you drink and BAL is dependent upon sex, weight, and a few other things. But the references seem to pretty much agree on the following rules of thumb for a standard adult:-
1 pint beer: 24%mg within an hour (can be up to 35%mg, depending upon strength of beer which clearly varies)
1 measure spirits: 12%mg within an hour
1 small glass wine: 15%mg within an hour.
The body (liver) then evacuates alcohol at a pretty constant rate of 15%mg per hour - although the references do admit that depending upon physiology it can actually be anywhere between 8 and 25 %mg/hour.
That stuff most of us had some idea about, but certainly it helps work out where we are after a good night out.
Now to the interesting bit - what the various studies gave as effects of alcohol. The various reports, papers and medical textbooks were pretty consistent. From them I came up with the following:-
11%mg - Reduced ability to maintain correct airspeed or flightpath under high workload
15%mg - 1/3 of pilots in fatal accidents had this level or above in their bodies (from autopsy reports)
20%mg - UK legal flying limit. Significant increase in errors on RT, planning and correct following of procedures.
40%mg - US legal flying limit. Major effect on number of errors on RT and following procedures.
- Reduction in g tolerance by between 0.1 and 0.4g.
50%mg - Impaired ability to visually fix or track objects
60%mg - Consistent degredation of long term performance even on low workload tasks.
80%mg - UK legal driving limit
150%mg - loss of self control (exactly what is meant by this wasn't defined)
200%mg - double vision, some loss of memory
400%mg - Loss of consciousness.
Three other notes were interesting...
(1) from a study where they tanked pilots up to 150%mg which was that afterwards when BAL had gone down to zero, visual impairment and disorientation could occur up to 7 hours afterwards.
(2) All the studies agreed that under high workload alcohol degraded pilots' performance much more than under low workload.
(3) Up until very high alcohol levels, virtually all the degredation was of judgment or ability to follow procedure, rather than of actual physical skills.