What if… Air Blank is Not Zero?

What if… Air Blank is Not Zero? 

Here are a couple of questions from our mail box about air blanks that are specific to the Alcomonitor CC, but can be generalized to all EBTs.  

First of all, here’s a little refresher about air blanks.  DOT regulations require that an EBT perform an air blank prior to a confirmation test to demonstrate that there is no alcohol remaining in the instrument from a prior test, and that the instrument is starting from zero.  Most instruments today automate the air blank procedure so that the operator need only observe the process.  

Q.  Will the Alcomonitor CC allow the operator to proceed with a confirmation test if the air blank is not .000? 

A.  No.  The Alcomonitor will display the message “High Blank” and will abort the test sequence.  Each model of Intoximeter instrument handles this situation in a different way, but as a rule the instruments will not proceed with the confirmation test sequence if the air blank is not .000.  

Q.  What does the Alcomonitor CC operator do when confronted with the “High Blank” message? 

A.  DOT regulations allow the operator to start a second test to attempt to get a zero air blank. 

If the second attempt to get an air that reads .000 is not successful, then the instrument must be taken out of service.  The instrument may be placed back into service upon successfully passing an Accuracy Check (the regulations use the term “External check of calibration.”) 

It is rare that an instrument does not give a zero air blank.  Possible reasons for a non-zero air blank include an extraordinary high level of alcohol blown into the instrument on a prior test; not waiting an adequate time after a very high positive test (15 minutes is more than adequate); re-using a subject’s mouthpiece that has alcohol in it; foreign contamination on the sensor or air passage of the instrument; and a sensor that is failing and needs replacement.