As I mentioned in the latest “Top 3 Science links” post, for most of North America, New Year’s Eve signifies two things: a fresh start and/or alcohol. Sadly, the latter means that some of us will make bad decisions tonight, often calling for a breath test administered by a friend or, more than likely, by a police officer.
The problem with giving someone a breath test right after said person has consumed alcohol stems from “mouth alcohol”, which is any alcohol that is present and unabsorbed in the mouth at the time of the breath test. Mouth alcohol can heavily affect breath test results, often leading to hugely false results. So, how long should a police officer or a friend wait after your last drink before giving you a breath test?
Previous studies have examined this question. Gullberg (2001) found that the time needed for mouth alcohol to dissipate is inversely proportional to the subject’s breath alcohol concentration (BrAC). This means that it takes less time for the results of a breath test to stop being affected by mouth alcohol when it is administered to a person with a high BrAC than when it is administered to a person with a low BrAC. In addition, Buczek and Wigmore (2002) found that frequent breath tests help mouth alcohol dissipate faster than normal breathing does.
Most of the studies that have been conducted in the past to assess the minimum wait time before administering a breath test, however, were done on alcohol negative subjects, meaning participants who had not previously consumed alcohol. This most recent study, published in the Journal of Forensic Sciences, is one of the first to look at this phenomenon in alcohol positive subjects.
In this study, Kari Sterling, a scientist at the Orange County Crime Lab, had seven alcohol positive subjects, five male and two female, participate in a study to evaluate how quickly mouth alcohol dissipates.The first part of the study looked at mouth alcohol dissipation in caused by normal breathing, while the second part of the study looked at mouth alcohol loss during continuous breath testing.
First, the participants consumed low doses of alcohol, 0.03-0.06g/210L, and then rinsed their mouths with vodka just before undergoing the breath test. Sterling then tested their breath for traces of alcohol after intervals of 1-5 minutes. She found that after 1 to 2 minutes, breath alcohol concentration decreased on average by 20.4%, with the results ranging from 3.2% to 47.9%.
The second part of the study looked at rate of alcohol dissipation during continuous breath testing. Here, Sterling tested the participants after they had consumed low levels of alcohol and high levels of alcohol (0.06-0.13g/210L).
The breath alcohol concentration (BrAC) decreased by more than 0.020g/210L between the first and the second test. It took an average of 9.35 minutes, ranging from 4 to 13 minutes, for the participants to reach their unbiased BrAC after rinsing their mouths with vodka. The unbiased BrAC is the “true” value, the one that should go on the file of a person arrested for driving under the influence.
This study confirms two things: the need to duplicate breath tests, which enables the acceleration of alcohol dissipation, and that an observation period lasting a minimum of 15 minutes is sufficient for mouth alcohol to dissipate, allowing for an accurate breath test to be administered.
The holidays are about being with loved ones and having a good time not about being locked in the back of a cop car, so please, this year, drink responsibly.
Sterling, K. (2011). The Rate of Dissipation of Mouth Alcohol in Alcohol Positive Subjects Journal of Forensic Sciences DOI: 10.1111/j.1556-4029.2011.02023.x
Buczek Y, Wigmore JG. The significance of breath sampling frequency on the mouth alcohol effect. Can Soc Forensic Sci J 2002;35(4):185–93.
Gullberg RG. Breath alcohol analysis in one subject with gastroesopha-geal reflux disease. J Forensic Sci 2001;46(6):1498–503.