Breath Tests (Intoxilyzer 9000)
If you gave a breath sample after a Houston DWI arrest, it was almost certainly analyzed by the Intoxilyzer 9000: the breath-testing instrument used by the Texas Department of Public Safety. Prosecutors present its result as a precise measurement of your blood alcohol concentration (BAC). In reality, the Intoxilyzer 9000 is a machine making an estimate based on assumptions that aren’t true for everyone, and its result can be challenged in several ways.
How the Intoxilyzer 9000 actually works
The device doesn’t measure the alcohol in your blood. It measures alcohol in a sample of your breath and then converts that figure to an estimated BAC using a fixed assumption called the partition ratio: 2,100 to 1. The problem: real people vary. Studies put the actual ratio anywhere from roughly 1,700:1 to 2,900:1. If your true ratio is higher than the machine’s assumption, the Intoxilyzer will report a BAC higher than you actually have: potentially pushing a sober-range reading over the legal limit.
Common ways breath tests go wrong
- Mouth alcohol. Alcohol trapped in your mouth, from a recent drink, mouthwash, dentures, a burp, or acid reflux/GERD, sits far more concentrated than the alcohol in your breath from your lungs. Even a tiny amount can dramatically inflate a reading. This is exactly why Texas requires a 15-minute observation period before the test.
- A botched observation period. The officer is supposed to continuously watch you for 15 minutes to make sure you don’t burp, regurgitate, or put anything in your mouth. Officers routinely look away, do paperwork, or start the clock incorrectly. A broken observation period undermines the whole result.
- The disabled histogram. The Intoxilyzer 9000 can produce a histogram: a real-time graph of your breath sample that flags irregular breathing and mouth-alcohol contamination. Texas deliberately runs the machine without this feature, discarding a built-in scientific safeguard. Its absence is a legitimate line of attack.
- Calibration, maintenance, and certification. The instrument must be properly maintained and the operator must hold a current certification. A lapsed certification, a gap in the maintenance log, or a deviation from protocol all support a challenge to the result.
- Medical and physiological factors. Diabetes, GERD, low-carb/keto diets, and other conditions can affect readings.
Watch: Breath Test Results Explained
Two short explanations of how breath test evidence actually works in a Texas DWI case, and what your options are at the roadside.
Blowing under .08 is not a free pass
Should you blow into a roadside portable breathalyzer?
You can refuse a breath test, but know the consequences
Texas’s “implied consent” law means refusing a breath test can trigger a driver’s license suspension through the ALR process, and police can seek a warrant to draw your blood instead. Whether refusal helped or hurt your case is something a lawyer evaluates based on your specific facts, but either way, the result can be challenged.
Think your breath test was wrong? Call Blass Law at (713) 664-4000. We obtain the maintenance and calibration records, scrutinize the observation period, and expose the assumptions the machine got wrong.
(Related: blood test defense · field sobriety tests · DWI cost)
Related: How we challenge DWI tests · Blood test defense & lab errors · Field sobriety test defense
Reviewed by Jay Blass Cohen, founder of Blass Law PLLC, ACS-CHAL Forensic Lawyer-Scientist, certified Drug Recognition Expert, and SFST instructor, serving Houston since 2009. This article is general information, not legal advice for your situation. Prior results do not guarantee a similar outcome.