DUI Breathalyzer Accuracy
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National Safety Council, Committee on Alcohol and Other Drugs, "Recommendation of the Subcommittee on Technology," Appendix M, page 145 (1996 printing).
Whether acceptably accurate or not, breath analysis in DUI investigations is the most convenient and economical method for the police, and the most convenient and least embarrassing or painful for the arrestee. As a result, the California DUI attorney will probably encounter some sort of breath analyzing instrument in 70 to 80 percent of his drunk driving cases.
There are a number of different breath analyzing machines in use today. The most commonly encountered of these in DUI cases is the Intoxilyzer Model 5000, of which there are now a number of different versions. The second machine most commonly encountered by today's California DUI lawyer is the BAC DataMaster, followed by the Intoximeter EC/IR and the Draeger Alcotest 7110 and portable 7410.
Each of these machines utilizes its own mechanism for analyzing the alcoholic content of exhaled vapor. With the exception of the Breathalyzer, however, all use a common method: infrared spectroscopic analysis (the Breathalyzer employs the "wet chemical" technique). These machines operate on the principal that alcohol vapor captured in a chamber will absorb light waves of a certain frequency when beamed through it. The more alcohol present in the chamber (i.e., the higher the percentage of alcohol in the breath sample), the more light is absorbed. In theory, then, determining the alcohol concentration of the sample is simply a matter of measuring the amount of light that reaches a receptor at the other end of the chamber; the more light, the lower the alcohol content in the breath. A computer then translates the figure into blood-alcohol concentration, using the blood-breath partition ratio.
In approaching a DUI case involving a breath analysis, the California DUI defense attorney should be aware that there are a large number of potential problems, both theoretical and operational. There exists a broad range of factors that can render any result of blood-alcohol analysis - breath, blood, or urine unreliable. As seen in the following subsections, additional problems unique to breath analysis add to this unreliability.
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