Calibration Frequency - Evidential Breath Analizer

harry

Super Moderator
#21
The instrument is only part of the equation. How about the operator (both contribute to errors)? Maybe it is easier to 'cast doubt' on the 'competency' of the operator if you had a hard time finding fault with the instrument.
 
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T

Tungsten

#22
The instrument is only part of the equation. How about the operator (both contribute to errors)? Maybe it is easier to 'cast doubt' on the 'competency' of the operator if you had a hard time finding fault with the instrument.
Hi Harry, Thanks very much for your input, good thinkin'!

I have a letter in front of me regarding the competency of the Garda Training Manual on the EBA from the Medical Bureau of Road Safety (University College of Dublin) the official body in Ireland who approves/calibrates the device. (The Intoxiliser is NOT certified by INAB. It is approved, supplied and tested (calibrated) by the Bureau pursuant to Section 6 of the Road Traffic Act, 1994. The MBRS is accredited to ISO1725 standards by INAB)

In the letter the Buerau notes that "There is nowhere in the course notes that indicate to the operator that they should not proceed with an Evidential Breath Test if the values are outside the temperature and relative humidity mentioned".

There is sufficient evidence that the test was performed at 14.5C outside of the capacity of the instrument.

Competent training? NOT!:nope:
 
T

Tungsten

#23
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.

 
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BradM

Staff member
Admin
#24
There is sufficient evidence that the test was performed at 14.5C outside of the capacity of the instrument.
Ok, let's accept that as a fact. Which is why you need to determine how much of an effect that would have on the indicated measurements. That is one estimated value of the entire uncertainty of this measurement process. I certainly don't mean to bore you with a bunch of "Calibration lingo", but for your situation, I do think it is important. Which is why I quote Harry below:

The instrument is only part of the equation. How about the operator (both contribute to errors)? Maybe it is easier to 'cast doubt' on the 'competency' of the operator if you had a hard time finding fault with the instrument.
Precisely. hence, the entire measurement process needs to be taken into account. As you stated the accuracy of the instrument is two digits (would that be +/-.01?), but that is only part of this picture.

You seem to have one decent line of defense about the variance due to using averages. Maybe if you could develop a total uncertainty, that would give you a second defense.
 
T

Tungsten

#25
Re: Calibration Frequency

You're in Ireland, so I have no idea what the laws might be. In the US, assuming evidence is admissible to begin with, the idea is to convince a jury that the calibration status of a device used in a particular instance is questionable--reasonable doubt.
Thanks very much for your input Jim. Ireland is pretty much the same jury system as in the States. I don't think I'll have much of a problem to convince the jury.

The judge is a different story.

Actually, I'm from the States (Orange County, CA), working in Ireland for the last two and a half years. :mg:
 
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T

Tungsten

#26
Ok, let's accept that as a fact. Which is why you need to determine how much of an effect that would have on the indicated measurements. That is one estimated value of the entire uncertainty of this measurement process. I certainly don't mean to bore you with a bunch of "Calibration lingo", but for your situation, I do think it is important. Which is why I quote Harry below:



Precisely. hence, the entire measurement process needs to be taken into account. As you stated the accuracy of the instrument is two digits (would that be +/-.01?), but that is only part of this picture.

You seem to have one decent line of defense about the variance due to using averages. Maybe if you could develop a total uncertainty, that would give you a second defense.
Hi Brad, thanks kindly for your input. There is a generous 17.5% uncertainty budget in place in Ireland which would cover pretty much all areas of relevant uncertainty.

The other fact is that in reality a 0.5 degrees C difference in temp would not make much of a difference in the outcome of the result.

Here, I am only questioning legality, compliance, effectiveness of operator training, and the reliability of a device which is set to an average of an obsolete system exists only in a few countries in the world.

Luckily I don't have to deal much with reliability to convince the jury, simply because how reliable any test can be if the convicting device is set to an average, uses an average blood/breath partition that is, outside of its stated operating temperature range?
 
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