Attacking Breath Results: How a DUI attorney handles breathalyzer evidence.
DUI cases are unique because of the scientific evidence used by law enforcement to arrest and convict. Attacking the breath results in a DUI case is a very important task for any DUI attorney because a jury will often put a lot of weight into the breath results. As impressive as the breathalyzer science is, it is important to understand the profound flaws that are inherent in this evidence.
How a breathalyzer works in a DUI Case:
The law prohibits driving while impaired, and a driving with a blood alcohol level above a certain threshold (0.08%). Measuring blood alcohol level in a driver necessitates that law enforcement get access to the person’s blood. This can be done, of course, through a needle. A less intrusive method was developed in the 1980’s, using a person’s breath to extrapolate and measure their blood alcohol level.
The theory behind a breathalyzer is as follows: Blood vessels that line a person’s lung will allow alcohol to diffuse through the lining of the person’s lungs into their breath. When the person exhales, alcohol that passed from their blood vessels into their lungs can be measured by a machine that traps and analyzes the person’s exhaled breath.
Problems with the accuracy of breathalyzers: They are NOT nearly as accurate as people think.
As you probably figured out, measuring a person’s blood alcohol content is very difficult using breath measurement. First and foremost, the rate of diffusion across the lining of the lungs varies significantly amongst various races, ethnicities and even between genders. The measurement of blood alcohol level using breath involves “co-efficients” or assumptions that are applied across the board. While these co-efficients may be accurate for a small percentage of the population, they are not accurate for everyone and can result in a wide disparity between the measured blood alcohol level and the person’s actual blood alcohol level.
Other sources of error for breathalyzers:
Other sources of error inlcude:
-Medical conditions that render the readings falsely high
-Issues during the absorption phase, where a blood alcohol level reading can be off by as much as 200%!
-Fuel Cell technology in the device that can be erroneous when the unit’s battery’s are not fully charged