Thursday, May 16, 2013

BAC calculator

The National Transportation Safety Board's recommendation this week that states consider dropping the legal limit for driving while intoxicated from a blood alcohol level of .08% to .05% was big news all over the country.  I spotted an article in our local press today:

"That's about one drink for a woman weighing 120 pounds, two for a 160-pound man. A "drink" means 12 ounces of beer, four ounces of wine"

I don't claim to be the world's foremost expert, but I immediately recognized that something important was omitted here. The missing ingredient is time.  It takes time to drink, and BAC is basically a math problem between the amount of ethanol, body mass, and time.  Basically, your body can't metabolize the alcohol in one standard drink (about a half ounce of pure ethanol) every hour, so if you consume a drink every hour over a period of time, your BAC slowly starts to build up. If you drink faster than one per hour, the concentration of alcohol builds up more quickly. It has nothing to do with tolerance, it's just math. 

If the 160 lb. man drank two 12 oz. standard American beers evenly during his first hour of drinking, he would be at about .025% to .035% at the end of that hour--not .05%. It is however, true that the third beer in hour one might put him over .05% at the end of an hour--it would be close. If he drank four in hour one, he'd be getting perilously close to the current legal limit of .08%, as he would with six in three hours. Throttle back to five Buds during a three hour televised football game, though, and he is still comfortably below .08%. Since he has slowed his consumption, his liver is dealing a bit more effectively with his mouth, though still not at equilibrium. 

My favorite online blood alcohol calculator is the Drink Wheel, from Intoximeters, Inc.--the company that manufactured the gas chromatographs I was trained to use a long time ago. The flame ionization detector and the Poropak Q column are still on the tip of my 37 degree Celsius tongue, 38 years later.  It's called the drink wheel because long before the PC and decades before the Internet, the drink wheel was a circular contraption made of two discs of card stock that you could rotate around to select weight, beverage, and time to produce an estimate. Sure wish I had saved one of those gizmos. We used to hand them out right and left.

It is, however, only an estimate.  Govern yourself accordingly, and err on the side of caution.


Steve said...

My problem with lowering the BAC limit is that, unless we somehow change our procedures in dealing with DUIs, it is not likely to make the roads any safer. Therefore, it seems just another way to limit freedom and raise money. While I don't disagree with the idea that even a .05 BAC is enough to affect a person's driving, does it effect it enough to really matter? Secondly, my guess is that even at the current BAC limit, at any given time, there are hundreds or thousands of people over the limit driving the roads of Nebraska. If we drop the limit to .05, that number will drastically increase. There is no way law enforcement can manage to get them all off the road in either case. We're left with catching a few before they have a crash, or discovering some afterward. Once, "caught", these folks typically go to detox or jail or are cited and released depending on the situation. They go to court, pay a fine, maybe get their license suspended, then go about their lives just as they always did. I doubt if the fines really amount to much more than it costs to catch them and process the cases, so it's probably not a money making deal either. What's the point?

Also, I'm quite sure a lot of people at .05 (or even .08) still drive better than a completely sober person who is drowsy or using their cell phone while driving. I suggest leaving the limit where it is and altering the penalties so that actually do some good toward lowering the number of impaired drivers on the roads. There needs to be some leeway. A person driving perfectly well who is pulled over for a taillight being out and found to be over the limit for the first offense does not deserve the same penalty as someone who was just involved in a fatal crash and found over the limit. A second offense should be much more severe and include at least some mandatory jail time. A third offense ought to be a life sentence. It is obvious from simply reading the papers that the current penalties do not keep people from driving drunk. If we're serious about keeping them off the roads, changing the limits will not do a thing unless we change the penalties.

Steve said...

So, an hour or so after my first comment, I read about a guy up in Omaha (I think it was) who was arrested after nearly hitting a police car for his eighth DUI. He had only been out of prison a few days before getting smashed and jumping behind the wheel. He was something like four times the legal limit. He gets another 12-year sentence at age 37, and will probably be back on the roads before he turns 44. I'm not sure if it's legislators or judges who are to blame, but the revolving door of DUIs going to jail and repeating their crimes needs to stop. How many people have lost their lives to these chronic offenders? How many more will?

Mark said...

I'm not a fan of these "calculators" as it gives a "license" to drink and drive. Most drinkers can't remember how many drinks they consumed (just two beers offisher) and these tools imply that there is an upper amount of alcohol that you can still safely imbibe.

I also hate to see news reports refer to the BAC of .08 as a limit. Again this implies that anything below that is OK. Most laws indicate that .08 or higher allows for a legal presumption (that can be disputed) that the driver is impaired. It is not a limit but a level of legal presumption.