Re: Calibration Frequency
Calibration is simply verifying the instrument is operating like it is intended. So either the instrument has been working like it should, or not.
The instrument has a tolerance, and there is error with testing methods. That tolerance and error may/ may not be a factor in testing.
Say.. you are testing Blood Alcohol content, and it's important if the actual BAC is .08 or .1. If the instrument is only accurate to within .05, say, then you may have a case. If it is accurate to like .01 or better, I don't think you would get too far with that.
Now, if this instruments has a "calibration" program that must be ran prior to each use, that is different.
I would think you would be interested in determining the repeatability of the instrument. How reliable is this thing?
Bottom line: This instrument is suitable to be making the claims during testing, or it is not. Your burden is to prove in court that the instrument is/ was not suitable.
Brad, thank you for your input. I have no data for repeatability of the unit. The accuracy of the device is 2 digits, acceptable. At this time all I've got is the subject's actual readout results.
The cycle of a test is as follows:
Blank... 000 (making sure there is no residual alcohol in the system (e.g. from a previous test. The value given by the machine MUST be zero)
Simulator Check 1... 035 (this is the first self-cal cycle PRIOR to the first blow of the subject. 035 used as a "standard" is the maximum allowed BrAC in Ireland (035ugm in 100ml of deep lung breath))
Blank... 000
Breath Specimen 1... nnn (the first blow of the subject)
Blank...000 (making sure that there is no alcohol remaining in the chamber. Preparation for the second blow)
Breath Specimen 2... nnn (the second blow of the subject)
Blank... 000 (making sure that no alcohol remains in the system)
Simulator Check 2...035 (self-cal, final)
To answer your question whether the instrument is suitable and/or reliable to make reliable claims? It is NOT. EBA's are widely criticized in forensic science regarding their accuracy and repeatability. Their operating principle is based on Henry's Law, which states that there is a fixed ratio exists for a fixed ratio of concentration of alcohol in water at a fixed temperature, therefore the ratio of alcohol in water is fixed. True. In theory, there is a constant ratio exists between the concentration of alcohol in the blood and the concentration of alcohol in the alveolar air of the lungs.
Now, here comes the interesting part, which I think I could challenge in court.
The average ration among human beings is generally accepted at 1:2100, that is, the same weight of alcohol will be contained in one cubic centimeter of pulmonary blood, as in 2.1 liters of deep lung breath. and most of the EBA's are set to this ratio.
But this is just an AVERAGE!
The actual ratio of any given individual can vary from 1:1500 to 1:3000, with a resultant error in ANY breath analysis arising from the 1:2100 ratio.
The subject device, the LION Intoxilizer 6000IRL is set to a blood/breath partition of 1:2300, which is near to the ratio of young, healthy 30 years old individual (1:2280). The subject is much, much older, with a chronic lung disease. It has been proven that both increasing age and lung disease can cause dramatically increased blood/breath partition ratios.
In this case the subject was tested with a device which is set to an average, a "one-size-fits-all". I'd call this the "convicted by a printout".
Fortunately, there are only few country remains which uses EBA's. It has been determined that such tests scientifically not convincing enough to demonstrate as "inherently reliable".
Consequently, the legal challenge mounted on behalf of the plaintiff should be considered in this light.