BAC & Breath Test Challenges Austin DWI

BAC Evidence in a Travis County DWI — What the Number Proves and What It Doesn’t

Texas law defines intoxication in two ways under Penal Code §49.01: either the loss of normal use of your mental or physical faculties by reason of alcohol, or a blood alcohol concentration of 0.08 or more at the time of driving. When your Austin DWI attorney reviews a breath or blood test case, the first step is requesting the full maintenance file. When the Travis County Attorney’s Office has a breath or blood test result above 0.08, it leads with the per se BAC theory. But a BAC number from an Intoxilyzer 9000 or from the Travis County Medical Examiner’s toxicology laboratory is only as reliable as the process that produced it. A machine output is not a verdict. A lab result is not a confession. Both are challengeable on technical grounds that are specifically obtainable through open records requests and discovery.

Every Austin DWI lawyer should request the Intoxilyzer 9000 maintenance file from day one. It is the breath testing instrument used by the Austin Police Department for DWI breath tests in Travis County. The specific machine used in your test has a maintenance log, a calibration record, and an error log — all obtainable. The operator who administered the test must hold a current certification to operate the Intoxilyzer 9000 under Texas DPS rules, and that certification has a renewal requirement. The required 15-minute observation period before the test must be documented. Any gap in the maintenance record, any lapsed certification, or any deviation from the testing protocol supports a challenge to the reliability of the result.

Blood draws in Travis County DWI cases are typically analyzed at the Travis County Medical Examiner’s Office toxicology laboratory. The chain of custody from the venipuncture through the lab analyst is a specific, documentable sequence that must be unbroken and properly recorded at every link. We request the complete lab file — not just the summary result — on every blood draw DWI case in Travis County. As a DWI attorney in Austin, this is non-negotiable. Call 512-599-9999 today.

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DWI BAC 0.11 — Austin APDDismissed

DWI BAC 0.15 — Travis Co.Dismissed

DWI Blood Draw — Travis Co. MEDismissed

DWI Breath Test — IntoxilyzerDismissed

DWI Refusal — Travis CountyDismissed

DWI BAC 0.09 — AustinReduced

Past outcomes do not guarantee future results. Every case is evaluated on its individual facts.

Charged with DWI Based on BAC Evidence? Get a Free Case Review

Breath and blood test results can be challenged. Chain of custody gaps, machine calibration failures, and improper procedure all create suppression arguments. Tell us what happened and an experienced Austin DWI attorney will review your case at no charge.

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Two Ways Texas Proves DWI — Two Ways We Challenge Both

Theory	What Prosecution Uses	Legal Standard	Our Challenge
Per Se BAC ≥0.08Penal Code §49.01(2)(B)	Intoxilyzer 9000 result or Travis County ME lab test	BAC at the time of driving	Machine maintenance, calibration, operator cert, 15-min observation, retrograde extrapolation
Loss of Normal UsePenal Code §49.01(2)(A)	Officer’s observations, SFST results, dashcam	Impaired at time of driving	SFST protocol violations, medical conditions, fatigue, medications, Austin road conditions
BAC ≥0.15 EnhancementPenal Code §49.04(d)	Breath or blood result ≥0.15	At time of test	Same challenges + retrograde extrapolation to time of driving
Retrograde ExtrapolationExpert testimony — contested science	State expert estimates BAC at drive-time from test-time	Estimated calculation	Absorption rate, food, metabolism, individual variables — expert cross-examination

Austin DWI BAC defense — Intoxilyzer 9000 maintenance records and Travis County Medical Examiner blood draw

Breath Tests vs. Blood Draws — How Each DWI Lawyer Austin Uses to Challenge BAC in Travis County

Intoxilyzer 9000 breath tests. The Intoxilyzer 9000 converts a breath alcohol measurement to a BAC estimate using a 2,100:1 partition ratio — assuming 2,100 mL of alveolar breath contains the same alcohol as 1 mL of blood. This ratio is a population average. Individual partition ratios vary significantly across the population — from approximately 1,700:1 to 2,900:1 in research studies. For individuals whose actual ratio is higher than 2,100:1, the machine will report a BAC higher than they actually have. We challenge the partition ratio assumption, the machine’s maintenance and calibration records, the APD operator’s current certification, and the 15-minute observation period documentation on every Travis County Intoxilyzer 9000 case.

Blood draw warrants. APD officers routinely obtain blood draw warrants under Texas Transportation Code §724.017 when defendants refuse the breath test. Blood draws analyzed at the Travis County ME’s toxicology lab must have a documented chain of custody from the phlebotomist through the lab analyst. The sample must be properly preserved with the correct anticoagulant-to-preservative ratio and stored under refrigeration. Improperly preserved samples can ferment after collection, producing additional ethanol not present at the time of the draw. We request the complete lab file on every Travis County blood draw DWI case.

Austin BAC DWI defense attorneys Mark Hull and Allison Tisdale — breath test and blood draw challenges in Travis County

How We Challenge BAC Evidence in Travis County DWI Cases

Technical BAC defense requires knowing what records to request, what to look for, and how to present the challenge in the Travis County Courts at Law or District Courts.

01

Request the complete Intoxilyzer 9000 maintenance file

We request the maintenance and calibration log for the specific instrument used in your test, the APD operator certification records for the officer who administered the test, and the instrument’s error log through open records. Any maintenance gap, failed calibration, or lapsed operator certification supports a challenge to the reliability of the result.

02

Verify the 15-minute observation period was properly documented

Texas DPS regulations require the officer to continuously observe the defendant for 15 minutes before administering the breath test to prevent mouth alcohol contamination. We verify whether this period was properly documented in the officer’s notes and on the Intoxilyzer 9000 printout. Deviations from the protocol affect result reliability.

03

Challenge the partition ratio and retrograde extrapolation

If the County Attorney’s Office uses expert testimony to link the test-time BAC to the drive-time BAC, we examine the assumptions: absorption phase, elimination rate, food consumption, and the specific physiological variables that affect the 2,100:1 partition ratio for this particular individual.

04

Request the complete Travis County ME blood draw lab file

We request the complete toxicology file from the Travis County Medical Examiner: collection documentation, phlebotomist qualifications, tube type and anticoagulant-preservative ratio, refrigeration and storage logs, chain of custody, analyst certification, and gas chromatograph calibration records. We examine every link.

05

Examine for post-collection fermentation

Improperly preserved blood samples can ferment in the collection tube, producing additional ethanol after collection. If the sodium fluoride content is insufficient or the sample was stored at elevated temperature, the BAC measured at the lab may be higher than the actual BAC at the time of the draw. We examine preservation documentation on every Travis County blood draw case.

06

Present the challenge to the Travis County Attorney’s Office

Allison Tisdale prosecuted DWI cases before joining the defense. She knows how the Travis County Attorney’s Office evaluates its BAC evidence, where the documentation is most likely to have problems, and how to present a documented challenge that moves a case toward dismissal.

BAC Defense in Travis County — 20+ Years of Technical Knowledge

Mark Hull has challenged breath test and blood draw evidence in Travis County DWI cases for over 20 years. BAC challenges require specific technical knowledge of the Intoxilyzer 9000 process, the Travis County ME’s blood testing procedures, and the partition ratio science that underlies breath testing. That knowledge comes from years of practice in these specific courts against these specific machines and labs.

Allison Tisdale prosecuted DWI cases as a Texas state prosecutor before joining the defense. She knows how the Travis County Attorney’s Office evaluates its BAC evidence and where documentation problems produce dismissal. We carry a 5.0 rating across 363 Google reviews and Over 930 dismissals or rejected cases since 2021.

◆ 20+ Years Austin Criminal Defense

Mark Hull has defended Travis County DWI cases for over two decades. Over 930 dismissals or rejected cases since 2021.

◆ Former State Prosecutors on Staff

Mark Hull and Allison Tisdale both prosecuted DWI cases before joining the defense. They know how Travis County builds DWI prosecutions — and exactly where they fall apart.

◆ 20+ Years in Travis County Courts

Regular appearances at the Blackwell-Thurman Criminal Justice Center. We know the County Attorney prosecutors, the DA’s DWI unit, and how the Travis County docket moves.

◆ Over 930 dismissals or rejected cases since 2021

Travis County, Williamson County, Hays County, and surrounding Central Texas courts.

Over 930dismissal or rejected cases since 2021

5.0Google Rating (363 Reviews)

20+Years in Travis County Courts

BAC & Breath Test FAQ — Austin DWI Attorney Questions Answered

What people ask about breathalyzer results, blood tests, and BAC in Travis County DWI cases.

What is the legal BAC limit for drivers in Texas?+

The legal BAC limit in Texas for adult drivers is 0.08 under Penal Code §49.01(2)(B) — the per se intoxication standard. However, Texas can also prove DWI through the impairment standard: not having normal use of mental or physical faculties, regardless of BAC. For drivers under 21, any detectable amount of alcohol while driving triggers a DUI under TABC §106.041 — no 0.08 minimum. For commercial vehicle operators, the federal limit is 0.04. A BAC at or near 0.08 is specifically challengeable — an Austin DWI attorney should evaluate the measurement methodology.

How can an Austin DWI attorney fight a breathalyzer test?+

An Austin DWI attorney challenges Intoxilyzer 9000 results on multiple independent grounds: the machine’s maintenance and calibration records (obtainable through open records), the APD operator’s current certification status, the required 15-minute continuous observation period documentation, the instrument’s error log, and the 2,100:1 partition ratio assumption that converts breath alcohol to blood alcohol concentration. A maintenance gap, a lapsed certification, or an undocumented observation period can all support suppression of the breath test result.

Can I refuse a breathalyzer in Texas and should I?+

You can refuse a breath test in Texas under Transportation Code §724. A refusal triggers an ALR suspension of 180 days on a first refusal (versus 90 days for a first failure) and can be introduced as consciousness-of-guilt evidence in the criminal trial. APD routinely obtains blood draw warrants under §724.017 when defendants refuse, so blood evidence is often collected regardless. Neither choice eliminates the Austin DWI attorney’s ability to challenge the evidence — the Fourth Amendment analysis of the stop, the SFST challenge, and the blood draw chain of custody challenge are all still available after a refusal.

Can a breath test result be challenged in Travis County?+

Yes. The Intoxilyzer 9000 used by APD is a specific numbered instrument with its own maintenance history, calibration log, and error log — all obtainable through open records. A machine with documentation gaps, a lapsed calibration, or a history of reliability issues produces results that are specifically questionable. An Austin DWI attorney should request the complete maintenance file for the specific instrument used in your test, not just the test printout result.

Can a blood draw result be challenged in Travis County?+

Yes. Blood draw results analyzed at the Travis County Medical Examiner’s toxicology lab can be challenged on chain of custody grounds (any documentation gap from collection through analysis), preservation grounds (improper anticoagulant-to-preservative ratio that can cause in vitro fermentation producing additional ethanol after collection), analyst certification grounds, and gas chromatograph calibration grounds. An Austin DWI attorney should request the complete lab file — not just the summary result — on every blood draw DWI case.

What is retrograde extrapolation and how does an Austin DWI lawyer challenge it?+

Retrograde extrapolation is used by prosecutors to estimate your BAC at the time of driving based on a test administered later. A state expert calculates the drive-time BAC by working backward through your estimated elimination rate. An Austin DWI attorney challenges retrograde extrapolation by examining: whether you were in the absorption phase (still processing alcohol) when tested, your individual elimination rate (which varies significantly across individuals), food consumption that affects absorption, and other physiological variables. Courts in Travis County recognize retrograde extrapolation as contested science subject to expert cross-examination.

What happens to my case if I refused the breath test in Austin?+

A refusal has two legal consequences: the ALR suspension period is 180 days on a first refusal versus 90 days for a failure, and the refusal can be introduced as consciousness-of-guilt evidence at trial. APD routinely obtains blood draw warrants under §724.017 when defendants refuse — meaning blood evidence is frequently collected anyway. The Austin DWI attorney’s ability to challenge the Fourth Amendment basis of the stop, the SFST administration, and the blood draw chain of custody is fully intact after a refusal.

Is 0.08 the only way Texas can prove DWI?+

No. Texas Penal Code §49.01 defines intoxication two ways: a BAC of 0.08 or above (per se), or not having normal use of mental or physical faculties (impairment). The prosecution can charge both theories simultaneously. The impairment theory relies on the officer’s observations and SFST results. The per se theory relies on the breath or blood test result. An Austin DWI attorney challenges both: the per se number on technical grounds (machine maintenance, chain of custody), and the impairment theory by challenging SFST protocol compliance and non-alcohol explanations for observed clues.

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BAC & Breath Test Defense — Austin DWI Lawyer

BAC Evidence in a Travis County DWI — What the Number Proves and What It Doesn’t

The Number Is the Start, Not the End

Two Ways Texas Proves DWI — Two Ways We Challenge Both

Breath Tests vs. Blood Draws — How Each DWI Lawyer Austin Uses to Challenge BAC in Travis County

How We Challenge BAC Evidence in Travis County DWI Cases

BAC Defense in Travis County — 20+ Years of Technical Knowledge

BAC & Breath Test FAQ — Austin DWI Attorney Questions Answered

Austin DWI Attorney Resources

Austin DWI Lawyer

First-Time DWI Defense

BAC & Breath Test Defense

DWI Conviction Consequences

DUI Defense (Under 21)

Texas DWI Laws

DUI vs. DWI in Texas

Austin Criminal Defense

What Our Clients Say

DWI Breath Test or Blood Draw in Austin? Challenge the Evidence.