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Vomit Rule: Breath test requires 15-minutes of clear mouth


Excerpted from Iowa DPS Datamster DMT Manual

Lawyers practicing exclusively in the area of criminal law with an emphasis in OWI, or, Operating While Intoxicated or Under the Influence—sometimes called DUI in other states— defense will tell you that they watch carefully the conditions under which an officer administers the Datamaster DMT breath test.

Datamaster DMT breath test results are admissible if they are properly maintained, certified, and operated. Proper operation includes strict adherence to the Datamaster DMT operator manual.

One requirement that DMT test administrators must know well is the 15 minute deprivation period. The 15 minute deprivation period ensures the test subject has nothing in his or her mouth for 15 minutes before administration of the test. It is documented on the Datamaster DMT test result receipt. Why?

Foreign objects and substances can trigger false positives. Tobacco, chewing gum, food, and other substances can absorb residual mouth alcohol and exaggerate breath test results.

The machine has some self-diagnostic ability but it may not be able to completely rule out a false positive test result. That requires a fail safe method for testing breath without foreign objects and substances interfering with the result.


The machine, however, does have a “slope detector” that measures whether dynamic alcohol levels increase or raise and then rapidly diminish—causing a so-called “negative slope.” If the machine senses a negative slope, it will throw an error code called an “invalid sample." Protocol requires a 15 minute deprivation period if the officer intends to retest. Therefore, the design of the machine concedes that a negative slope is not a measure of alveolar, or, deep lung, alcohol, because the expectation is that alcohol will steadily increase, not increase and fall back down. A negative slope is therefore an indication that the machine is reading residual mouth alcohol—possibly absorbed in chewing gum or chewing tobacco or other substances that should have been cleared during the 15 minute deprivation period.

Since vomit introduces substance or substances in the mouth, observation of a test subject vomiting requires a new 15 minute deprivation period although the instructions merely allow and do not require rinsing with water.

If you or a loved one have been arrested for OWI (DUI) in Cedar Rapids, Iowa City, or other Iowa community, contact us for a free initial consultation utilizing best CDC practices for social distancing. We are here for you during this legal crisis. But remember that a blog is not legal advice and that sending unsolicited information to an attorney does not establish an attorney-client relationship.

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