THE FREQUENCY OF APPARENT ACETONE IN A GROUP OF BREATH ALCOHOL DATA -STATISTICAL TREATMENT AND FORENSIC IMPLICATIONS

The potential presence of interfering substances (specifically acetone ) is a concern in the forensic reporting of evidential breath alcohol analysis. As a result, manufacturers have designed instruments to moni tor its occurrence through various hardware and software features. Thi s paper is a retrospective study where 35 945 duplicate breath samples from BAC Verifier DataMaster instruments are evaluated for the freque ncy of 'interferant' values greater than or equal to 0.010 g per 210 1 ethanol equivalent. A total of 264 (0.74%) of the duplicate samples h ad an interferant value on the first sample only, while 235 (0.66%) ha d interferant values on the second samples only. A total of 77 (0.21%) of the duplicate samples had in interferant values on both breath sam ples and only in these cases could the presence of measurable acetone even be considered. The occurrence of interferant results appeared als o to be instrument-dependent with 55.7% of the interferant values on t he first breath sample occurring on nine (13%) of the instruments disp laying such results. The occurrences of interferant values on the firs t breath sample did not conform to the Poisson distribution (P < 0.000 1) for the instrument with the largest number of occurrences, while th ere was conformance for other instruments evaluated. Finally, similar to 23 cases (0.064%) remained where the presence of acetone is a possi ble consideration. Several issues are presented that the forensic scie ntist should consider when attempting to explain an apparent interfera nt result in an individual case. It should be remembered that measurem ent results need to be interpreted in their context, and data analysis concerning an instrument's performance should be considered.