The published Intoxilyzer 9000 margin of error
CMI, Inc., the manufacturer of the Intoxilyzer 9000 used by Texas DPS, publishes a manufacturer-tolerance margin of error of ±0.005 g/210L at low BACs and ±0.01 g/210L at higher BACs. The Texas Breath Alcohol Testing Program adds its own protocol requirements: two breath samples within 0.02 of each other, calibration checks before and after, and biennial inspection of the instrument.
Beyond the published margin: real-world variability
The published margin assumes proper calibration, proper sample collection (deep lung air), and proper operator administration. Real-world cases routinely show variability beyond ±0.01 due to: temperature variation in the testing environment; radio-frequency interference from nearby equipment; mouth alcohol from belching, GERD, or recent food/drink within the 15-minute observation period; operator failure to observe the suspect for the full 15 minutes; instrument drift between calibration checks.
The 0.08 question and the 0.005 buffer
For a 0.085 reading, the margin of error analysis matters enormously. The State must prove BAC of 0.08 or above beyond a reasonable doubt. If the published instrument margin is ±0.005, the true value could be anywhere from 0.080 to 0.090. That alone doesn't require acquittal, but it shifts the burden of proof analysis. Add real-world variability and the case for reasonable doubt grows.
How we challenge breath tests
(1) We subpoena the instrument's calibration and maintenance records. (2) We retain a breath-test expert to review the certification, the printouts, and the operator's qualifications. (3) We cross-examine the operator on the 15-minute observation period and the deep-lung-air sampling. (4) We file motions in limine to exclude testimony beyond the scope of the operator's personal knowledge.
References
In our practice defending Texas criminal cases, we have represented clients in Collin, Dallas, Denton, and Tarrant County criminal courts on the full Texas Penal Code and Health & Safety Code spectrum. Reggie's prosecutor background in Dallas County means we know the State's evidentiary playbook; Njeri's trial-trained motion practice anchors the suppression-driven defense work.
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