So, in 10 hours essentially from typing this, someone will be driving. Tonight they have had 6 cans of Guinness draught (440ml, 4.1% abv), 1 can of Guinness original (440ml, 4.2% abv) and 3 bottles of Leffe blonde (330ml, 6.6% abv). They’re just finishing the last of it now but started drinking around three or four hours ago.
Scientifically speaking (i.e. not rubbish like “1 unit an hour” - let’s have something backed up by evidence) what will their BAC be when they start driving?
The one unit an hour isn’t ‘rubbish’. I took lots of psychopharmacology classes in undergrad and grad school and it is true. That is roughly the rate the average person metabolizes alcohol. I have done those experiments on myself many times with a breathalyzer. I am not too good at metric alcohol measurements but you are looking at about 10 standard drinks because Guinness is a low alcohol beer but it is offset by the Leffe Blonde which is higher than normal. You said they started drinking 3 or 4 hours ago so the clock starts then. They will be fully clear of alcohol in another 7 hours and technically legal to drive before that. If you want to build in some margin for error, the people in question should blow a 0.00 in less than 9 hours.
Well, their weight would be an important consideration. Given the info you’ve given us, I would assume their ABV would be marginal, if they’re over, say, 140-150 pounds.
If you want a cite, try this. Enter 10 beers, 14 hours, and 150 lbs, male, and you should get 0.03% BAC.
My thinking is that with most drugs people talk about half lifes. Don’t see why alcohol should be different. But I am absolutely ignorant of the pharmacology so maybe there’s a reason it should be broken down at a constant rate.
Blood alcohol levels don’t get metabolized on a half life schedule. It is literally about a .02 concentration drop every hour for an average person. That doesn’t mean that the person won’t be impaired in some way. Really bad hangovers can last for a day or more but the breathalyzer and blood tests won’t register it.
Trust me on this one. I took the classes that said that is what to expect and then did the experiment many times on myself. It is true. 10 standard drinks will go to 0.00 blood alcohol content in about 10 hours as the liver works hard to metabolize them.
If the alcohol dehydrogenase is saturated, the rate of oxidation can be zero order in concentration of ethanol. Based on the above comments, I’m assuming that’s the case here.
[QUOTE=wikipedia]
Many physiologically active materials are removed from the bloodstream (whether by metabolism or excretion) at a rate proportional to the current concentration, so that they exhibit exponential decay with a characteristic halflife (see pharmacokinetics). This is not true for alcohol, however. Typical doses of alcohol actually saturate the enzymes’ capacity, so that alcohol is removed from the bloodstream at an approximately constant rate.
[/QUOTE]
And there we have it.
The other question, of course, is whether this person will be too hung-over to drive in the morning.