| Drunk driving charges are difficult and technical cases | | | | suspect is still absorbing alcohol from their last drink |
| for the DWI defense lawyer to challenge. This is | | | | when the breath test is given. |
| especially true when a suspect provides a breath | | | | 4. Computer programing used in these machines |
| sample to the police after being arrested for driving | | | | assume the temperature of the accused person's |
| while intoxicated. Many technical issues arise with | | | | exhaled breath is 34 degrees Centigrade. (Core body |
| breath test cases which require focused preparation | | | | temperature for humans is 37 degrees Centigrade) |
| by the defense attorney. This is the first of several | | | | For every breath degree over 34 this assumption |
| articles to help clients, and DWI defense lawyers alike, | | | | results in the overestimation of the person's breath |
| understand the important issues involved in defending | | | | alcohol content by about 6.8%. Since the machine |
| these charges and the breath testing machines. | | | | assumes the temperature of the suspect's breath is |
| 1. Many breath testing machines are designed to | | | | 34 degrees, additional assumptions must be made |
| analyze a sample of a person's breath based on | | | | upon interpreting the test results. |
| Henry's law. When a volatile chemical (ethanol) is | | | | 5. Alcohol in the mouth can lead to erroneous breath |
| dissolved in a liquid (blood) and brought into contact | | | | test results. Breath test machines claim to handle the |
| with a CLOSED air space, an equilibrium is formed and | | | | mouth alcohol problem with a computer program called |
| there exists a FIXED RATIO between the | | | | the "slope detector." There have been no scientific, |
| concentration of ethanol in the air space and the | | | | peer reviewed studies showing the slope detector |
| concentration in the liquid. (at a given temperature and | | | | works as advertised. |
| pressure) At equilibrium one can measure the | | | | 6. The margin of error for many breath testing |
| concentration of ethanol in the gas phase and predict | | | | machines is +/- 0.010 for the reference sample, and +/- |
| the concentration of ethanol in the liquid. The problem | | | | 0.020 for the suspect's breath sample. When |
| with the human lungs is that they are not a closed | | | | defending against breath test charges right at the legal |
| system and Henry's law does not exactly apply. | | | | limit, the margin of error for the machine allows the |
| 2. Breath test machines are also designed to produce | | | | criminal defense lawyer to argue the person's test |
| a breath alcohol result exactly corresponding to a | | | | results could have been as easily under the legal limit, |
| simultaneous blood alcohol sample. The machine | | | | as over the limit. |
| programing assumes the partitioning of alcohol from | | | | 7. Beyond this, the sample chamber can contain up |
| the blood into the breath is 2100:1. Not all persons | | | | to.019 gms alcohol/210 liters breath alcohol inside it |
| partition alcohol from their blood based upon this ratio. | | | | when the machine is reading a 0.00. This creates the |
| Studies show partition ratios as low as 834:1. Breath | | | | potential that residual alcohol in the sample chamber, |
| testing devices relying upon this assumption will | | | | not coming from the suspect's breath, will be used |
| overestimate the alcohol concentration of someone | | | | against the person accused of DWI. |
| blowing with a partition ratio less than 2100:1. | | | | Future articles will discuss how the DWI defense |
| 3. Many breath testing machines assume the person is | | | | lawyer can use other technical issues with breath test |
| in the elimination phase of alcohol consumption, rather | | | | machines to their advantage. |
| than the absorption phase. It is rarely known whether a | | | | |