The effect of breath alcohol simulator solution volume on measurement results

Breath alcohol simulator devices (simulators) containing alcohol and water solutions are used to calibrate and test breath-testing instruments. The manufacturers of simulators design them to contain 500 mL of solution. This study evaluated the variability observed among three different groups of data: one group (experimental) in which the solution volume varied from 400 mL to 600 mL, one group (control) in which the simulator volume remained constant at 500 mL for each aliquot, and finally one group consisting of field simulator measurements collected over time. The infrared breath test instrument employed was a BAC Verifier Datamaster. A one-way analysis of variance and the Cochran's C for equal variances were applied to the data. The results indicated that when the solution volume remained at 500 mL, there was nearly as much or greater within-run variability as when the volumes were varied from 400 mL to 600 mL. Both the experimental and control groups showed statistical significance for the one-way ANOVA and were considered within-run measurements. The high within-run instrumental precision (CV approx. 1%) probably accounts for these results. The field data, considered between-day measurements, had larger within-group variability and resulted in a nonsignificant ANOVA. Small variations from the 500-mL volume in a simulator do not result in a statistically significant difference where between-day measurements are evaluated.