Section 76 Slope Detector Does Not Always Work

• Library: DWI Experts and the Science of Chemical Tests 2014

Mouth alcohol can cause serious problems for breath testing, partly because the mechanism, called a slope detector, that is installed in the software of the Intoxilyzer 5000 and the BAC DataMaster does not always work. See Patrick Harding et al., The Effect of Dentures and Denture Adhesives on Mouth Alcohol Retention, 37 J. FORENSIC SCI. 999 (1992). It is the opinion of the author of this chapter that slope detectors, designed to detect mouth alcohol, do not work.

The problem is simple—the “slope detector,” or “mouth alcohol detector,” is only found when a machine that has IR technology cannot differentiate between alcohol from the lungs and alcohol from a contamination source from food particles, tobacco, GERD, etc. Because the breath test is dependent on an exhalation from the mouth, all sources of alcohol will be tested to make up the reading. This will cause a false high reading.

According to Missouri law, the blood-to-breath ratio has been established at 2100 to 1 (actual blood-breath ratio could be higher or lower and varies in individuals and between individuals). See §§ 577.012.2 and 577.037.2, RSMo Supp. 2012. This ratio means the reading on a breath-testing device multiplies by 2100 the alcohol molecules it reads in the sample from the mouth of the subject.

The mouth alcohol detection can work somewhat frequently when there is no alcohol in the subject’s blood stream (example—swishing alcohol then spitting it out and taking the test), but the mechanism (algorithm in computer processor of the machine) falls off in accuracy when consumed alcohol is mixed in the mouth with stomach or mouth sources of alcohol.

The various breath machines vary in effectiveness in flagging mouth alcohol and terminating the test and displaying the error message (invalid sample or a message depicting that there is an interfering substance present). The Intoxilyzer family of breath-testing devises (I‑5000, I‑8000, and even the new I‑9000) has great difficulty flagging mouth alcohol contamination. The European machine, the Evidenzer, and the National Patents...