Don't Hold Your Breath: The Knapp Court's Spectacular Misunderstanding of Basic Science
When Courts Mistake Legal Convenience for Scientific Rigor
The recent Minnesota Court of Appeals decision in Knapp v. Commissioner of Public Safety represents a troubling departure from sound forensic science principles and threatens to undermine the reliability of breath alcohol testing in Minnesota’s DWI cases.
As a forensic professional, I must speak out against this legal precedent and convenience over scientific validity.
The Science Behind the 15-Minute Observation Period
The 15-minute pre-test observation period isn't just an arbitrary legal requirement—it's a critical quality assurance protocol designed to ensure accurate breath alcohol measurements.1
During this period, officers must continuously observe the subject to detect any burping, belching, hiccuping (sometimes called hiccoughing), vomiting, or ingestion of materials that could introduce mouth alcohol, contaminate airways through microaspiration2, and artificially elevate test results.3
Why this matters scientifically:
Mouth alcohol from recent alcohol consumption, acid reflux, regurgitation, or dental work can cause falsely elevated readings
The DataMaster DMT measures alcohol vapor from lung air, but contamination from residual mouth alcohol can skew results
A 15-minute waiting period allows mouth alcohol to dissipate naturally
Continuous observation ensures no new contamination occurs during this critical window
The Court's Fundamental Misunderstanding
The Knapp court made several scientifically problematic determinations:
1. Conflating Legal Admissibility with Scientific Reliability
The court held that a certified operator and functioning machine are sufficient for admissibility, regardless of whether proper protocols were followed. This creates a dangerous false equivalency—a perfectly calibrated instrument can still produce unreliable results if contaminated samples are introduced.
2. Shifting the Burden of Proof Inappropriately
By requiring defendants to prove that observation period deficiencies actually affected their specific test results, the court ignores the fundamental principle that prevention is better than correction.
We cannot always retroactively determine if mouth alcohol contamination occurred without the proper observation period (but in some cases, we can, which I highlight in my recent paper on the limitations of mouth alcohol detection systems).4
3. Minimizing Protocol Violations
The court's statement that observation period deficiencies go only to "weight" rather than admissibility fundamentally misunderstands how forensic science works.
Contaminated samples aren't less reliable—they're invalid entirely.
Real-World Implications for Forensic Science
This decision creates several concerning precedents:
Erosion of Standard Protocols: If courts can dismiss established scientific protocols as mere technicalities, what prevents the abandonment of other quality assurance measures like calibration requirements or chain of custody procedures?
False Confidence in Technology: Modern breath testing devices are sophisticated, but they cannot always distinguish between alcohol from lung air versus mouth alcohol contamination. The court's suggestion that machine diagnostics alone ensure reliability demonstrates a misunderstanding of the technology's limitations.
Inconsistent Standards: The decision creates a troubling inconsistency where forensic laboratories must follow strict protocols for admissibility, but field testing can proceed with compromised procedures.
The Dangerous Overreliance on Machine Diagnostics
The court's emphasis on machine diagnostics as sufficient proof of reliability is particularly troubling given the documented limitations of breath testing devices.
Recent research, including my published article, The limitations of mouth alcohol detection systems in breath alcohol testing: Case reports, demonstrates specific cases where the DataMaster DMT failed to detect obvious mouth alcohol contamination despite all diagnostic checks passing normally.
Even more concerning, John Fusco, the creator of the DMT device, has acknowledged that the instrument's mouth alcohol detection system only catches contamination 85-90% of the time!5
Fusco said:
If you’ve got a person that's an 0.05 or 0.08, they stand a real good chance of fooling the instrument when it comes to mouth alcohol… Alcohol that's in the mouth is being then disseminated into the air that's already contains alcohol that's coming from the lungs… you can actually take a person who is 0.05, 0.06, 0.07, and pull that reading up to 0.12, 0.20… Now, but the key is here, you don't observe the waiting period.
This means that in 10-15% of cases with mouth alcohol present, the machine will provide a falsely elevated result with no warning to the operator.
Other investigators, such as Simpson, have found that the DMT fails to catch mouth alcohol about 50% of the time!6
These limitations make the 15-minute observation period even more critical—human observation serves as an essential backup when the machine's automated detection systems fail.
Unfair Burden on Vulnerable Populations
The Knapp decision creates a particularly unjust burden on defendants with medical conditions like gastroesophageal reflux disease (GERD), hiatal hernia, or other conditions that can cause spontaneous regurgitation.
These individuals are at higher risk for mouth alcohol contamination, yet the court's ruling requires them to:
Prove their medical condition affected the specific test—often requiring expensive expert testimony
Demonstrate the exact timing and impact of any regurgitation—difficult to prove retroactively
Bear the financial burden of challenging scientific evidence—despite lacking the resources of the state
This creates a two-tiered justice system where wealthy defendants can afford expert witnesses to challenge improper procedures, while those of modest means are left to accept potentially contaminated results.
Discouraging Law Enforcement Accountability
By excusing observation period violations, the Knapp decision removes incentives for proper police training and procedure compliance.
Instead of acting as gatekeepers for science in the courtroom, the court is actually encouraging shoddy science!
Why should departments invest in rigorous training protocols if courts will accept test results regardless of whether officers follow established procedures?
This is particularly troubling given that Minnesota's Bureau of Criminal Apprehension (BCA) has established clear core values, including:
Integrity: "Integrity is the cornerstone of public trust. This organization strives to always do the right thing."
Excellence: "We value excellence in our people and our work to continually provide the best service to our partners, the Minnesota criminal justice community, and the citizens of this state."
Unfortunately, BCA breath lab scientists have not consistently upheld these values when testifying in court, often downplaying protocol violations and overstating the reliability of compromised test results.
The Knapp decision essentially validates this approach, encouraging testimony that prioritizes conviction rates over scientific integrity.
The BCA's Policy Evolution: From Recommendation to Requirement
The Knapp court appears to have relied on an outdated understanding of BCA policy. While the BCA only recommended observation periods with the older Intoxilyzer 5000, since 2012 with the DMT, they have consistently required it as a mandatory protocol.
The current BCA DMT Operator Training Manual makes this clear, stating that operators must "ensure" there is no burping and that:
A test subject should be observed for a minimum of 15 minutes prior to administering a breath test to ensure nothing is placed in the mouth and nothing erupts into the mouth.
The policy evolution from recommendation to requirement reflected the BCA's recognition of advancing scientific standards."
Yet the Knapp court treated current mandatory protocols as if they were still mere recommendations, missing that the BCA's own manual states maintaining quality is "imperative" and requires operators to "ensure" proper observation.
When an agency's own training materials mandate strict compliance, courts shouldn't excuse violations as technicalities.
The Specific Problems in Knapp
The facts in Knapp present a textbook example of why a continuous observation period matters:
The deputy and Knapp were separated by a Plexiglass partition in a darkened squad car
The deputy was facing away from Knapp, relying only on a rearview mirror
The deputy's attention was divided between observation duties and other tasks
The observation period was interrupted when they moved locations
These circumstances make it impossible to ensure that no contaminating events occurred. The deputy's testimony that he "did not observe any burping, belching, or vomiting" is meaningless if he wasn't in a position to observe effectively.
A Better Approach
Courts should recognize that forensic science protocols exist for valid scientific reasons, not arbitrary legal technicalities. A more appropriate approach would:
Require strict adherence to observation protocols for admissibility
Recognize that protocol violations create doubt about reliability
Place the burden on the state to prove proper procedure compliance
Acknowledge that some violations are so fundamental that they render results inadmissible regardless of other factors
Conclusion
The Knapp decision represents a step backward for forensic science in the courtroom. By prioritizing legal convenience over scientific rigor, the court has created a precedent that could lead to the admission of potentially unreliable evidence in DWI cases.
As a forensic scientist, I continue to advocate for evidence-based approaches to breath alcohol testing. The 15-minute observation period isn't bureaucratic red tape—it's an essential safeguard that protects both the accuracy of our measurements and the integrity of our justice system.
The Minnesota Court of Appeals got this one wrong, and we can only hope that future courts will recognize the fundamental importance of maintaining rigorous scientific standards in forensic evidence.
Dubowski KM. Quality assurance in breath-alcohol analysis. J Anal Toxicol 1994; 18: 306–311.
Park J-S, Burton L, Van der Wall H, et al. Modified Reflux Scintigraphy Detects Pulmonary Microaspiration in Severe Gastro-Esophageal and Laryngopharyngeal Reflux Disease. Lung 2021; 199: 139–145.
Minnesota Bureau of Criminal Apprehension. DMT Operator Training Manual. Minnesota Department of Public Safety (2019).
Olson A. The limitations of mouth alcohol detection systems in breath alcohol testing: Case reports. Forensic Sci Int Synerg; 10. Epub ahead of print 1 June 2025. DOI: 10.1016/j.fsisyn.2025.100573.
Michigan Datamaster Breath Testing Seminar - Part 5 of 7, (2014, accessed 26 May 2025).
Simpson D, Kerby JA, E, Kerby Scott. Effects of mouth alcohol on breath alcohol results. International Journal of Drug Testing 2000; 3: 1–14.