Judge Carroll reversed himself last week and ruled that evidence of the 2100:1 breath to blood alcohol ratio was indeed relevant to both the charge of driving while impaired (28-1381(A)(1)) and to the charge of driving with an alcohol concentration of .10 or more within two hours of driving (28-1381(A)(2)).

Earlier in trial, Judge Carroll ruled the evidence was only relevant to the (A)(1) charge, and then, only if the state introduced evidence of impairment levels, evidence that all persons are impaired at .08 BAC, or if the state wanted the jury instruction on the presumptions of impairment.

In the past some city judges incorrectly assumed that evidence of the 2100:1 ratio was no longer relevant to any prosecution for DUI based upon changes in the definition of "alcohol content."

All current breath test devices, are designed with the assumption that a subject's breath-to-blood ratio is 2100:1.

In the real world this ratio ranges from 1706-3063 to 1, with a mean ratio of 2280 to 1. In theory, anyone having a ratio higher than 2100 to 1 will test lower by breath as compared to direct blood alcohol determination. Anyone lower than 2100:1 will test higher.

Expert testimony showed the 2100:1 ratio varied among individuals anywhere from 1100:1 to as high as 3000:1. Most people fell between 1700:1 and 3000:1.

If a person had a ratio of 1700:1, the IR5000 would over estimate their blood alcohol level by 20 per cent. Above 2100:1, the IR5000 would under estimate the level.

Only the comparison of a blood test with a simultaneously obtained breath test could reveal a defendant’s ratio, something not done in Phoenix.

The use of the 2100:1 blood-breath conversion factor does have important implications in close cases, particularly where a per se statute is charged.

In 1983 the Arizona Supreme Court recognized the relevance of the 2100:1 ratio in an (A)(2) case in State v. Fuenning, when it said, " . . . the manner in which the Defendant was driving, the manner in which he performed the field sobriety tests, and the videotape showing his behavior at the time he was booked . . . will be relevant to the jury’s determination of whether the test results are an accurate measurement of alcohol concentration."

The Fuenning decision also said, "We agree with defendant that the only ultimate issue is whether defendant had a BAC of .10% or greater. In each case in which a violation of subsection B [now (A)(2)] is charged, the state will present evidence of the test and the issue will be whether the test results were an accurate measurement of the defendant’s BAC at the time of the arrest. Typically, defendants will attack the margin of error, the conversion rate, the calibration of the test instrument, the technique used by the operator, the absorption and detoxification factors, etc."

Prosecutors argued the above language was rendered moot after the legislature changed the definition of "alcohol concentration" in 1988.