Motorists arrested for DUI/DWI, driving under the combined influence of alcohol and drugs, or any drinking and driving offense are offered a choice of an evidential breath test or a blood test. (When motorists are arrested for DUID – driving under the influence of drugs – they will be offered a choice of a blood or a urine test.)
Drunk driving cases may be based on many different breath test machines, including the E-PAS (a hand-held unit that is often administered roadside), or a variety of stationhouse breath-testing machines, such as the Intoxilyzer 5000, the EC/IR, the Draeger, the BAC Datamaster, and many more. The type of machine used will vary from jurisdiction to jurisdiction.
All breath testing in drinking and driving cases is an indirect measurement of blood alcohol content (BAC). Breath testing devices all engage in a conversion process, whereby a blood alcohol level is predicted on the basis of certain scientific assumptions, which may or may not be applicable to the person being tested. These scientific assumptions include drivers’ blood/breath partition ratio, their breath temperature, and many other factors.
Breath testing in a DUI/DWI always takes place after the time of driving (which is, of course, the relevant time in a drunk driving case), the number only becomes relevant through a process called retrograde extrapolation. Retrograde extrapolation is where the prosecution attempts to demonstrate the allegedly drunken driver’s alcohol level at the earlier time of driving based upon the later breath test results.
There are significant problems with this type of speculation, which provide opportunities for your criminal defense attorney to demonstrate reasonable doubt. Alcohol levels change over time, and the manner in which they change is subject to much variation. Stomach contents, the amount of alcohol consumed, the length of the drinking period, body weight, gender, elimination or “burn-off” rate, and other personal metabolic factors all interfere with retrograde extrapolation in a DUI/DWI arrest. In order for retrograde extrapolation to be meaningful or scientifically accurate, the expert must assume that the accused drunk driver is “post-absorptive” – an assumption not always true, since the absorptive phase can last for two hours or more.
In obtaining breath results, there are two types of breath test machines that may be used – infrared breath testing machines or fuel cell breath testing machines.
In the infrared device, the subject blows into a collection tube. Light passes from one end of the tube to the other, and the machine measures the amount of light beam that is diminished as it passes from one side to the other in the light spectrum of the alcohol molecule.
The fuel cell device measures the amount of oxidation that takes place on an electromagnetic chip. Then, the amount of the electrical charge is converted to a number, which supposedly represents the amount alcohol in the subject.
The first place to look when challenging a DUI/DWI breath test is the functioning of the breath test machine itself. The type of machine will vary from state to state, and from county to county within a given state. Whether the machine is an Intoxilyzer 3000, Intoxilyzer 5000, Intoxilyzer 8000, EC/IR I or EC/IR II, a Draeger or a BAC Datamaster, the machine must be working properly to give a reliable result. This means ensuring that the accuracy checks, calibration records, usage logs and maintenance history are all properly documented and don’t reveal any problems.
An experienced California DUI/DWI defense lawyer will know just how to investigate each area of potential problems. When these problems are revealed, they may result in the breath test results being excluded, or may just be used to attack the weight of the evidence. A criminal defense DUI/DWI lawyer will know how to use these issues to the driver’s best advantage.