Breath Testing Errors

All states have now passed laws lowering the blood-alcohol level to .08%. And most people suspected of violating the law are given breath tests to determine the level of alcohol in their blood. The breathalyzer will take a small sample of the suspect’s breath and estimate how much alcohol is in it — and, from that, estimate how much may be in the blood.

And what that machine says is pretty much the end of it. There will be no second tests. There will be no cross-examination of the machine. Are these machines so reliable and accurate that we have permitted them to become judge and jury?

Scientists universally recognize an inherent error in breath analysis, generally of plus or minus .01%. That means that if everything is working perfectly (an unlikely scenario), a .13% breathalyzer test result can be anywhere from .12% to .14%.This has been acknowledged by courts across the country (see, for example, People v. Campos, 138 Cal.Rptr. 366 (California); Haynes v. Department of Public Safety, 865 P.2d 753 (Alaska); State v. Boehmer, 613 P.2d 916 (Hawaii), recognizing an even larger .0165% inherent error).

What does that tell us about the accuracy of these breathalyzers? Well, let’s take a test result of .10%. Taking inherent error into consideration — and assuming the machine was working perfectly, the officer administers the test correctly, and the suspect’s physiology is normal and perfectly average — the true BAC could be anywhere from .09% to .11%. In other words, the true BAC can be 10% in either direction — or, put another way, anywhere within a 20% margin of error.

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