If Someone Drinks Often And Can Hold Their Liquor, Does That Mean It Will Take Longer For Their BAC Level To Rise To A Level Of Legal Impairment To Operate A Vehicle?

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People who have a so-called “high tolerance” for alcohol will still get drunk. They may be better able to conceal the effects of alcohol better than other people because they may have more practice masking some of the obvious signs. But in terms of level of intoxication and BAC, it’s generally going to be the same. People who are not seasoned drinkers get in trouble because they are less familiar with the feelings of being intoxicated, and therefore, don’t mask those feelings the way a seasoned drinker would.

Can Even One Drink Impair A Driver’s Ability To Operate A Motor Vehicle To Some Degree?

The notion that one drink can impair a driver’s ability to operate a motor vehicle may seem correct. I remember a pilot I once represented who testified in his own defense that drinking even a small amount of alcohol will affect a person, if only to an infinitesimal degree. However, some studies show that a person driving with a BAC of less than 0.05% is less likely to get into an accident than a teetotaler. Perhaps this surprising conclusion was due to the fact that people who drink to the level of 0.05% or less usually are more responsible, tending to be a little more careful after having a drink or two. There may be some small degree of impairment, but such people will compensate for having consumed alcohol by taking their time and driving more carefully.

The legal limit for driving a commercial vehicle is 0.04%. That BAC level is a nationwide standard. For pilots, the level is 0.00%. Pilots cannot drink alcohol for at least 12 hours before they get into a plane. While commercial drivers and pilots have special training, the law imposes higher standards because the vehicles they operate can pose a threat to many more people that the ordinary operator.

How Does Alcohol Actually Affect The Human Body?

Alcohol is a depressant and affects the way the brain functions. It numbs the senses. To be technical, we shouldn’t be concerned about blood alcohol content. We should be concerned about brain alcohol content. While to measure the amount of alcohol in somebody’s brain, there is a very strong correlation between behavior and the amount of alcohol in a person’s blood. Until a person has fully absorbed alcohol, there is no uniform distribution of alcohol in the body, and presumably in the brain. Once absorbed, alcohol is eliminated at a fairly constant rate. At that point, a reasonable inference can probably be drawn that, at a certain blood alcohol level, a person could have some impairment in their motor functions, in the way they think, and in the way they perceive things.

How Do Breath Tests Measure Intoxication And How Much Someone Has Had To Drink?

There are different instruments and different technologies that measure how much someone has had to drink. In breath testing, for example, there is infrared spectroscopy and fuel cell technology.

Infrared spectroscopy works through the use of infrared light. Infrared light is passed through a vapor sample containing a person’s breath. That light is absorbed by some of the chemical bonds in the alcohol molecule. The reduction in the intensity of the infrared signal is then assumed to correlate with a certain blood alcohol content. That works great in theory, except that infrared spectroscopy is not necessarily specific for alcohol.

We have similar specificity issues with fuel cell technology. A fuel cell works like a battery. There is a positive terminal, an anode, and a negative terminal, a cathode. Between the anode and cathode is a substrate of porous material. When the breath sample is injected into that substrate, it will induce an electrical current between the anode and cathode. The strength of the current is deemed to be a measure of the amount of alcohol in the breath.

The Dräger Alcotest 7110 used in New Jersey combines fuel cell and infrared technology with the aim to make the breath alcohol measurement more specific for ethanol. While both the infrared and fuel cell technology are not necessarily specific for ethanol, they’re not specific in different ways. Dual technology breath testing instruments increase specificity. While this doesn’t eliminate the specificity problem, it does reduce it. For example, people who are diabetic, particularly people who have difficulty controlling their blood sugar, produce isopropanol as a byproduct of diabetic metabolism. Isopropanol can cause a signal three times that of ethanol and induce error by affecting both infrared absorption and fuel cell current in the same proportions as ethanol. Consequently, a person who is diabetic or in ketosis may blow a high number with little or no alcohol in their system.

Fuel cell and infrared technologies are accurate in making their measurements of voltage and light absorption, respectively, thereby leading to inferences about ethanol content in the blood. When used in combination, these technologies make breath alcohol measurements more specific for ethanol.

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