This Raleigh Durham Cary DUI/DWI attorney would like to comment once again on the limitations of the breathalyzer machines used throughout the Raleigh, Durham, Cary area. Aside from the many limitations I’ve already discussed on this blog — another example of the unreliability of the breathalyzer is that the results will vary depending on the way the motorist breaths into it.
A scientist at the University of Washington has determined:
“By far, the most overlooked error in breath testing for alcohol is the pattern of breathing….The concentration of alcohol changes considerably during the breath…The first part of the breath, after discarding the dead space, has an alcohol concentration much lower than the equivalent BAC. Whereas, the last part of the breath has an alcohol concentration that is much higher than the equivalent BAC. The last part of the breath can be over 50% above the alcohol level….Thus, a breath tester reading of 0.14% taken from the last part of the breath may indicate that the blood level is only 0.09%.” – published in The Champion.
Other studies have confirmed these results. In one such study a group of men drank a decent amount of alcohol and then took a breathalyzer test with varying breathing techniques. The results indicated that holding your breath for 30 seconds before exhaling increased the blood-alcohol concentration (BAC) by 15.7%. Hyperventilating for 20 seconds immediately before the analyses of breath, on the other hand, decreased the blood-alcohol level by 10.6%. “How Breathing Techniques Can Influence the Results of Breath-Alcohol Analyses”, 22(4) Medical Science and the Law 275. The results of a similar study were reported in “Accurate Measurement of Blood Alcohol Concentration with Isothermal Breathing”, 51(1) Journal of Studies on Alcohol 6.
