If asked to envision a “typical” arrest for drunk driving, most people in Maryland would likely detail a scene depicting a person standing on the side of the road, blowing into a hand-held breath testing device. In Maryland, any such breath test administered on the street is inadmissible evidence at trial. Only the breath test taken at the police station is admissible if and only if proper operating procedures were followed.
That such a scenario embodies the general public’s perception of drunk driving charges should come as no surprise; most correctly believe that one registering a blood-alcohol content level of .08 (the near-universal legal standard for indicating intoxication) will result in their arrest. It is important to know that a breath test reading of .08 or more does not mean an automatic conviction.
How does a breath-testing device work?
The alcohol one consumes when drinking eventually finds its way into their bloodstream and makes its way to their lungs. In the lungs, it comes in contact with oxygen, which causes a small portion of it to vaporize. One then expels that gaseous oxygen from their body with each breath.
The ratio between the alcohol content on one’s breath remains in equilibrium with that in their blood. Breath testing devices thus measure the alcohol content of a sample of breath to determine this blood-to-breath alcohol ratio. According to the Alcohol Pharmacology Education Partnership, when making this measurement, these devices assume a ratio of 2100:1.
The trouble with breath testing device assumptions
The problem with this assumed ratio is that in reality, one’s actual blood-to-breath alcohol ratio can vary from 1500:1 to 3000:1. Factors that may influence such variation can include:
- Body composition
Even the amount of food in one’s stomach can influence their level of intoxication.
This extreme potential variance presents the potential for a high margin of error with breath tests (indeed, the National Motorists Association reports it to be as high as 50%). This may help one in mounting a challenge to the validity of breath test results.