Alcohol BAC information

8.Alcohol Information

8.1 Properties of Alcohol

There are a few different  types of Alcohol

Other over-the-counter products, such as mouth wash, contain a form of alcohol. Listerine® is 26.9% alcohol[2].

For purposes of this book, and for DWI, we will be referring to Ethyl alcohol.


Alcohol itself has no odor/ a faint odor. It is actually the congeners that are added to the alcohol which give it its smell. Most officers will acknowledge this on cross examination.

Alcohol is formed through a process known as fermentation. Fermentation is carried out by different bacteria and yeasts. This is important, because alcohol can ferment in the yeast of a blood sample that was not properly stored or obtained.

Alcohol is categorized in the depressant class of drugs. To affect the brain, and in turn the body, alcohol must be absorbed into the blood stream and circulated throughout the central nervous system, and the rest of the body.


8.2 “Proof” of alcohol

The proof of an alcoholic beverage is its alcohol content multiplied by 2. So, a drink that is 80 proof will be 40% alcohol.

Typically, most beers are around 5% alcohol, wine is around 10-20%, and distilled spirits are between 40-50%alcohol. A rough rule of thumb is that one 12 oz. glass of beer, one half glass of wine, and one shot of vodka or distilled spirit, will all be around the same alcohol content, commonly referred to as one drink.

8.3 Absorption

This is the phase when alcohol is being absorbed into the blood and various bodily organs. Alcohol is mainly absorbed through the entire gastrointestinal (GI) tract[3].


8.3.1 Factors Affecting Absorption

Alcohol gets absorbed differently from person to person. A rough estimate is that each drink equals around .015 BAC and takes about an hour to absorb. Again, everyone is different. There are many factors that affect the rate of absorption. Food

People who eat on an empty stomach will absorb alcohol quicker. This is due in part to the food acting like a sponge in the stomach. Gender

Generally, women will have a higher BAC than men if both consume the same amount. Weight

The more someone weighs, the lower their BAC will be compared to someone who weighs less, assuming everything else is equal.


8.4 Distribution

This is the phase where alcohol has been transferred to the blood and is being distributed throughout the body.


8.5 Elimination

Alcohol is a poison. Accordingly, the body wants to get rid of it, and it is also broken down. This process is called elimination. The number one thing that contributes to elimination is time. Over time, alcohol will be eliminated from the body.

Officers will often ask someone how much they had to drink. However, officers do not as often ask over what period of time. The amount of time is just as important as the amount consumed to determine a BAC. One can reasonably have a six pack over the course of an entire night and still have a BAC of zero.


8.5.1 Elimination Rate

The rate at which alcohol leaves the body is referred to as an elimination rate. It is different foreveryone, and even changes in the same person. The average elimination rate is .015.


8.5.2 Factors Affecting Elimination Rate

Many things that affect the elimination rate are the same as those that affect absorption rates. They include gender, amount and type of alcohol ingested, and any food ingested.



8.6 Peak BAC

All of the phases will generally have some overlap to them, primarily, because alcohol is generally consumed over time. Even if one drinks really quickly, the phases still will have some overlap, but it should/could be brief.

One way to think of it is to fill a plastic cup with water, poke a hole in the bottom and put a very narrow straw in it. As the alcohol is sitting in the cup it will be in the absorption phase. As it enters the straw, it will be distributing. As it leaves the other end of the straw, it will be eliminating. Because the alcohol takes time to both absorb and eliminate, while some alcohol is being absorbed, the alcohol that was in there previously can now be eliminated.

As long as elimination occurs faster than one is absorbing, the person’s BAC will be going down. If the body is absorbing more alcohol than it is eliminating, or if the body has not yet started to eliminate, the BAC will be going up (Also referred to as rising BAC).

At some point in this formula, there will be an equilibrium. That point is known as the peak BAC, or maximum BAC. The problem in determining this peak BAC, is that besides gender, weight, and age, the BAC of a given individual is constantly changing. While it is often referred to as a straight line on a graph, that is not necessarily the case

8.7 Widmark Formula / Hypothesis

The Widmark hypothesis is a formula that determines BAC based upon certain variables. It works in a linear/ “zero-order” manner.

8.8 Retrograde Extrapolation

Retrograde extrapolation is the process of determining the BAC at the time of driving, or any other given time, based upon a BAC at a later date, such as when a blood or breath test was administered.

In order to make a retrograde calculation, one must assume absorption and elimination rates (which then includes food eaten, gender, weight, etc.), when the alcohol was consumed, the amount of alcohol and concentration, and the Widmark “r” factor.

The value of the prior BAC will be based upon averages. It is impossible to determine an exact BAC at any given time due to all of the factors that must be considered. Certain factors, like absorption and elimination rate can never be precisely known.

8.9 Impairment due to Alcohol

While the first half of the chapter was more devoted to BACs, and therefore more useful to a Per Se DWI charge, this part deals with how alcohol impairs someone. This is more beneficial to a charge where the State must prove impairment (to any degree in N.H.) due to alcohol.

It is important to note that while alcohol will affect everyone, it will not affect everyone in the same way. People can build up a tolerance to alcohol, meaning it would require a greater amount of alcohol to impair them as compared to a non-drinker.

8.9.1Factors that may affect impairment Tolerance Food

[1]Garriott’sMedicolegal Aspects of Alcohol 5th Edition (2009) (hereafter referenced as Garriott’s). Ch.1 pg. 3

[2]Garriott’s Ch. 1 pg. 7

[3]Garriott’s Ch. 2 pg. 5