THE ALCOTEST 7310-SYSTEM: CONCEPT AND PERFORMANCE

*M. Schmidt, Ph.D.

SYNOPSIS

The breath tester Alcotest 7310 is designed to be part of a system containing the instrument and specially adapted equipment for calibration and employment. The system ensures both high performance and optium adaptation to user's conditions. By concept the purpose of the instrument is optium roadside screening with respect to a certain legal limit. The performance in respect to this purpose will be demonstrated by the results of police field trials.

INTRODUCTION

In this presentation, I first want to describe the Alcotest 7310 as a system for preliminary testing; second, I will present field results from Germany to demostrate what performance can be expected in real situations.

1) A single instrument can hardly incorporate all features needed for different applications. If it does, it might end up being overdesigned for most applications. Therefore, accessories are the best way to adapt the main instrument to an actual situation. Figure 1 shows the intrument with the battery pack detached. The battery packs can be individually charged, or exchanged, according to the requirement of the actual use. They are snapped to the instrument when in use.

A small suitcase is available for transporting one instrument and one pack of mouthpieces safely. This case can also be connected to the cigarette lighter of a car for charging the batteries. Proper charging is shown by a lamp outside of the case.

The calibrator for fast and safe calibration, which is described in the accompanying paper, and the charge unit for permanent charging are additional equipment.

We are convinced that this range of equipment is sufficient and helpful in using the Alcotest 7310

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National Draeger, Inc., P. 0. Box 120, 101 Technology Drive, Pittsburgh, Pennsylvania 15230, USA.

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successfully in all present ways of Preliminary Breath Testing. The performance of the unit is shown in Figure 2. Please note especially the ambient conditions.

2) The field test results are shown in Figure 3: 949 tests have been performed in Germany by the police with subsequent blood analysis. The figure shows the number of tests versus certain Alcotest 7310-readings. By comparing the later blood results with the reading, it turned out that the numbers shown right of each gap, denoting distinct threshold levels, would have been false positives in respect to this level. The levels used for this picture are .08% and .13% BAC (Blood Alcohol Concentration). By comparing the number of false positives to correct positives, the overall percentage would have been 7% and 14% for a .08% and .13% threshold. The percentage depends on the actual distribution: the more highly intoxicated people aretested, the better this ratio becomes. Accordingly, the false negatives, shown left of the gaps are 15% in both cases. In my opinion, this picture shows a good separation performance of the Alcotest 7310 for given thresholds. By interpreting these results, one must remember that all errors like possibly improper calibration, wrong handling, or inaccurate blood tests are contained in this performance picture.

The ratio of false to true readings of the Alcotest 7310 are shown in Figure 4. It can readily be seen that right next to the thresholds, the likelihood of a reading to be or false positive or negative is 40-50%, as expected for a threshold evaluation, and then it drops rapidly to zero.

To summarize, the Alcotest 7310 is part of a system which is well adapted to real preliminary breath testing situations. The performance in the field proved to be good with respect to the separation of drunk drivers above or below a certain threshold.

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Figure 1. The Alcotest 7310.

Figure 2. Stability of the Alcotest 7310.

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FIELD TEST RESULTS FR.GERMANY

Figure 3. Field tests results from the F.R.G. (N = 949).

Figure 4. Field test results: false negatives and false positives.

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