San Diego DUI Law Center

Are San Diego DUI Breath Tests Reliable?

A San Diego California DUI breath test is the most popular San Diego DUI chemical test.

But the reliability of some San Diego DUI breath tests may be questioned.

Courts can exclude breath test results because of unreliability.

In 2002, the Washington Supreme Court ruled a lady could not have her driver’s license suspended because of problems with the reliability of a DUI breath test. The lady challenged an administrative suspension of her driver’s license. The case looked at the reliability of thermometers used in DUI breath test equipment.

Thermometers are used to test the machines’ accuracy. DUI Breath Test operators test the machines by getting a reading from an alcohol and water mixture. The mixture must be kept at 34 degrees centigrade, and that is why the thermometer is important.

That Supreme Court ruled: because evidence was not produced to show that the thermometer on the machine had been certified as reliable, her license could not be suspended.

A court reversed DUI convictions on the grounds that drunk driving breath tests are inherently unreliable. In State v. McGinley, 550 A.2d 1305 (N.J. Super. 1988), a New Jersey Superior Court considered the consolidated appeals of four persons whose convictions involved DUI Breath tests.

While noting the New Jersey Superior Court had essentially taken judicial notice that the DUI Breathalyzer models “900 and 900A are scientifically reliable,” that court nevertheless considered new scientific evidence not previously available.

New scientific evidence showed:

1. The DUI breath test machine is designed to test persons having a 2100/1 blood-breath ratio. Such ratios in fact vary from 1100/1 to 3200/1. The variance can produce errors in test results. In fact, high readings were taken in 14% of the population.

2. The temperature of the DUI breath test machine itself varies, thereby affecting test results.

3. Body temperatures vary between human beings, additionally affecting DUI breath test results.

4. Hematocrit, or the solid particles in whole blood, vary – particularly between males and females – which further affects DUI breath test results.

Inherent unreliability exists in different San Diego DUI breath testing machines.

San Diego DUI Breath Test errors can be magnified if San Diego California DUI police do not follow proper procedures, such as Title 17 of the California Code of Regulations, including but not limited to continuously observing the subject for 15 minutes prior to breath testing, properly calibrating a San Diego DUI breath test machine, timely checking accuracy, testing blank specimens, and/or ensuring an arrested San Diego DUI person is not adversely affected by her or his ambient environment.

An excellent San Diego DUI Defense Lawyer will know how to challenge the reliability of a particular San Diego DUI breath test.