Minimum Breath Volume Requirement

The Alcohol Breath Test: Examining Minimum Breath Volume Requirements

The alcohol breath test is a common method used by law enforcement to determine blood alcohol concentration (BAC) during drunk driving investigations. However, the validity and accuracy of these tests have come under scrutiny due to issues with minimum breath volume requirements. This article will examine some of the key considerations around minimum breath volumes for breath tests.

Do minimum volumes really ensure an accurate sample?

While minimum volume requirements intend to collect alveolar air, some research suggests this goal is not always achieved in practice. Studies have shown high variability in the lung size and breath volume capabilities of different individuals based on factors like age, gender, and body size.

For example, those with smaller lung capacities may be forced to exhale more deeply to meet the 1.1 liter minimum, resulting in a potentially inflated BAC reading compared to someone with larger lung volume who can meet the requirement with a less deep breath.

As Michael P. Hlastala, Professor Emeritus at the University of Washington, notes:

“A consequence of continuing to use the old model is that subjects with larger lung volume may have a lower BrAC than a subject with a small lung volume because these subjects do not need to exhale as great a fraction of their vital capacity as subjects with smaller lung volume to fulfill the minimum volume exhalation required before stopping exhalation (usually ~1.5 liters).”

This suggests the minimum volume does not actually guarantee a sample of alveolar air in many cases. The variability in lung size and breath volume capabilities across the population means using a “one size fits all” minimum risks inaccuracy.

Do state laws define an acceptable breath sample?

Interestingly, many state statutes establishing BAC limits do not precisely define what constitutes an acceptable “breath” sample. Without a clear definition grounded in science, the minimum volume requirements used in practice appear largely arbitrary rather than evidence-based.

As one scientific paper notes:

“Although the scientists may have assumed that alveolar air is preferred for an accurate test, the law does not say that…. Instead, because ‘breath’ is undefined, the only logical interpretation of the statute is that ‘breath’ means the whole breath.”

This disconnect between the law and science allows room for legal challenges to the minimum breath volume requirements currently used by many instruments.

What are the legal implications?

Given the scientific uncertainties around minimum volumes, strict requirements could prejudice some defendants who are physiologically unable to provide an appropriate sample reflecting their true BAC.

For example, those with smaller lung capacities may be unable to exhale 1.1 liters without providing a disproportionately deep breath, leading to a falsely high reading. Yet refusal to provide a sample can also lead to severe penalties in some states.

This creates a difficult legal position for some drivers. Lawyers may consider arguing that individual physiological differences make the blanket minimum volume requirements improper and unreliable for determining actual blood alcohol levels.

Potential defenses around minimum volumes

For drivers charged with DUI based on breath test results, potential defenses lawyers may explore relating to minimum volumes include:

• Arguing the minimum volume is arbitrary rather than scientifically supported to ensure a proper alveolar air sample.
• Presenting evidence that lung volume/capacity varies significantly across the population, making any fixed minimum volume requirement unreliable.
• Pointing out state law definitions of “breath” are vague and fail to specify that only alveolar air is acceptable.
• Noting that differences in breath volume capabilities mean some individuals are forced to provide deeper lung air to meet the minimum, inflating their BAC results.
• Raising due process issues around refusing to provide a sample when inability to meet the minimum is physiological, not willful.
• Questioning the accuracy and reliability of results from instruments like the Intoxilyzer 8000 in light of flaws with minimum volume requirements.
• Consulting medical experts to assess the defendant’s actual lung capacity and ability to provide an appropriate breath sample.
• Introducing evidence about the defendant’s lung volume limitations and inability to satisfy the minimum volume without providing a disproportionately deep breath.

These kinds of arguments may convince the court that results over the legal limit were inaccurate and unreliable due to insufficient scientific foundation for the minimum breath volume requirements.

When is the minimum volume defense likely to succeed?

Like any legal defense, the success often depends on the specific facts and jurisdiction. But lawyers may have the greatest chances with minimum volume challenges in cases that show:

• The defendant made a good faith effort to satisfy the minimum but was physically unable due to lung capacity limitations.
• Medical evidence confirms the defendant’s physiology makes meeting the minimum volume inherently difficult if not impossible.
• The defendant’s two breath samples showed sharply differing results, indicating natural variability in breath volume is affecting accuracy.
• The defendant’s alleged BAC is only barely over the legal limit, so even a small amount of measurement error could produce an inflated result.
• Other evidence beyond the breath test shows lower intoxication levels, contradicting the BAC results.
• The applicable state laws are vague on defining an acceptable breath sample and rely on scientifically unsupported minimums.
• Previous cases have successfully challenged the minimum volume requirements for that instrument model or jurisdiction.

While not guaranteed to succeed, minimum volume requirements remain an area where skilled DUI lawyers can call into question the validity of breath test results in certain cases. Understanding the scientific and legal nuances is key.

Conclusion

The alcohol breath test is not as simple and foolproof as often assumed. Minimum breath volume requirements attempt to ensure valid BAC readings but have been criticized by scientists as unreliable and legally questionable.

Drivers or their lawyers may be able to challenge high breath test results in court by arguing these arbitrary minimums fail to account for individual physiological differences in lung size and capacity.

While success is not guaranteed, highlighting the scientific flaws and vagueness in state laws around minimum volumes could help undermine the accuracy of BAC readings over the legal limit in some cases. But achieving meaningful reform will likely require extensive advocacy and education on the complex science involved.