The Draeger 9510 is the most commonly used breath alcohol instrument in Washington DUI investigations.

The Draeger 9510 is the most commonly used breath alcohol instrument in Washington DUI investigations.

Stopped for a DUI? Here’s what you need to know about your breath test sample

The doubtful data behind Draeger 9510 breath results

Have you been stopped for suspicion of driving under the influence and given a breath alcohol test?

Here’s what you need to know:

The Draeger 9510 is the most commonly used breath alcohol instrument in Washington DUI investigations. Like the obsolete DataMaster, it analyzes breath to help police estimate the level of alcohol in a person’s blood, explains lawyer Ziad Youssef, of MyTrafficMan.net.

Most states have laws that set the legal limit for breath alcohol at .08 (Note: Utah recently reduced its limit to .05 and Canada imposes a 24-hour license suspension at .05).

This means anyone who blows a .08 is automatically assumed to be driving under the influence. However, that assumption has to be proven beyond a reasonable doubt, and recent developments in DUI defense strategies have created reason to doubt the instrument and its results, Youssef says.

How does the Draeger 9510 work?

The Draeger 9510 runs on software that the state has yet to properly validate. Software controls the data when the instrument is used to collect and test a breath alcohol sample. Every quarter second, sensors check and record flow rate, volume, breath alcohol level and time to ensure the minimum criteria for a breath sample is achieved.

Washington DUI law requires that the instrument only test “end expiratory air” – the last portion of air exhaled by the driver into the Draeger. The technical manual further clarifies that the minimum criteria for a valid sample requires at least 1.5 liters of breath exhaled and that the individual blow for at least five seconds. Blowing should only stop after the arresting officer notices the quarter-second readings of breath results are starting to plateau, meaning they’re not increasing at a rate greater than .04/second.

The instrument plots a graph of the breath result data for the officer and displays it on the built-in screen. When the graph starts to plateau, and the officer sees that at least five seconds have past and at least 1.5 liters of breath volume has been blown into the instrument, they have collected their first valid sample.

Valid vs. non-valid sample

A valid sample creates a graph that is always rising.

Any dip in results followed by a sharp rise indicates the presence of “mouth alcohol” or other interference which makes the result invalid.

Mouth alcohol refers to alcohol not coming from a person’s breath, but something else in the surrounding or ambient air or a contaminant in the driver’s mouth, like food particles, or other items that negate the validity of the test according to the Draeger technical manual. Graphs that decrease followed by a sudden increase indicate an invalid test, and the jury would have plenty of reason to doubt the breath result based on this data.

Using the graphing data at DOL and in court

Challenges to the reliability or accuracy of a Draeger 9510 breath test, or the functioning of the instrument generally, have not resulted in the inadmissibility of the test results. That means the hearings officer at a Department of Licensing hearing and the jury in a criminal trial will likely see the results, but since they are the “trier of fact,” they may consider the challenge in determining what weight to give the test result.

Since the driver bears the burden of challenging the weight of a breath test result after it’s been admitted at a DOL hearing, presenting evidence of an invalid test is critical to successful hearing.

And although the burden remains on the prosecution to prove the test is reliably over the limit, it’s equally important to present the graph(s) to a jury to create reasonable doubt.

Administrative rules that apply to both a DOL hearing and a criminal trial require that if during a breath test, interference or mouth alcohol is detected, the test shall be invalidated.

“I recommend asking for a jury instruction on what an invalid test is, so the jury can consider the rule on mouth alcohol or interference,” Youssef says. “Even if it’s not allowed, I recommend talking to the jury about what a valid test requires and questioning the toxicologist or Draeger technician about the technical manual and its requirements.”

Questions about your DUI or how to obtain and use your graphing data? Visit mytrafficman.net or call 360-734-0908.

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Focusing on DUI, MyTrafficMan’s lawyers serve clients in Bellingham, Bellevue, Ellensberg and Vancouver, WA as part of a broad network of legal resources focused on delivering the best legal care to each client. Learn more about their various legal services and initiatives at mytrafficman.net or visit on Facebook.

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