Operator error in breath tests?

The Intoxilyzers didn't fail. They faithfully detected the presence of alcohol when 1,147 drivers blew into them.

But the mistakes made by humans were so basic - did anyone notice, for example, that 0.009 is a bigger number than 0.005 - that they raise questions about training and oversight in the Philadelphia Police Department.

And at least one defense attorney, a DUI expert in Harrisburg with scientific training, argues that Pennsylvania's regulations are too weak to ensure that basic errors are caught and fixed statewide - an assertion that some in law enforcement dismiss.

City officials announced last month that police had been using four breath-testing instruments whose accuracy had not been proved in mandatory checks. The evidence in drunken-driving cases between September 2009 and November 2010 would be reviewed, District Attorney Seth Williams said.

Most convictions for driving under the influence rely on far more than a breath-alcohol test, which normally is administered after an arrest to get a measurable reading that will seal the case. Although the review will be a costly headache for overworked prosecutors and judges, most cases are unlikely to be thrown out. Letters were sent several weeks ago to lawyers for 416 defendants whose cases involved one instrument that was identified in February. None of them has requested a new trial, the District Attorney's Office said Friday.

In fact, it is not clear that the instruments in question registered an over-the-limit blood-alcohol concentration when they shouldn't have, or even that they were all calibrated incorrectly. The errors were in certifying that they were correct, so now there is no way to know that a 0.08 - the legal definition of drunk - was, in fact, a 0.08.

Thomas E. Workman, who teaches scientific evidence at the University of Massachusetts Dartmouth School of Law, used this analogy: "If you don't have an inspection sticker, it doesn't mean that the car is bad. It just means that you can't verify that the car is working correctly."

The Intoxilyzer 8000, a distant descendant of the original Breathalyzer (and the earlier drunkometer), is one of the newest and most common breath-testing instruments used for evidence by police around the country. It is the size of a toaster oven, weighs 17 pounds and typically is plugged in at the station. CMI Inc. of Owensboro, Ky., manufactures and sells the device for around $6,000 to $8,000 depending on configuration, features, and accessories.