Incidence of “Invalid Sample” Screen Messages on the Intoxilyzer® 5000C Obtained from Arrested Drinking Drivers in Toronto. Is a 15 to 20 Minute Wait Period Warranted?

Abstract

ABSTRACTA five-year retrospective study of “INVALID SAMPLE” screen messages obtained on the Intoxilyzer® 5000C from drinking drivers arrested in the City of Toronto was undertaken. There were 196 “INVALID SAMPLE” screen messages generated by 184 drivers and they could be classified as single or multiple occurrences and as to whether they were associated with the first or subsequent or multiple breath tests. The incidence was 1.7% of the total number of the drivers tested. Single “INVALID SAMPLE” screen messages (n=173) occurred with much greater frequency than multiple messages (n = 11). The distribution of single “INVALID SAMPLE” messages was nearly evenly divided, with 88 occurring prior to the first breath test and 85 prior to the second breath test. The time in police custody to the time of single “INVALID SAMPLE” message ranged from 27 to 223 minutes and from 59 to 199 minutes for multiple occurrences of “INVALID SAMPLE” messages. This time period precluded an exogenous mouth alcohol effect influencing the results. The time between the “INVALID SAMPLE” and the subsequent breath sample retest after single “INVALID SAMPLE” messages ranged from 2 to 61 minutes (mean 5 minutes), while the time period to retesting after multiple messages ranged from 3 to 65 minutes. The duplicate breath test results for all cases (single and multiple messages) were within 0.02 g/210L (truncated) and no third breath test was required. For breath tests that were conducted less than 20 minutes from the time of the “INVALID SAMPLE” screen message, no evidence of a mouth alcohol effect resulting in the next breath test being significantly higher due to mouth alcohol was observed. Although highly transient mouth alcohol cannot be excluded as the cause of the messages in this study, we provide evidence in support of the view that most of instances of “INVALID SAMPLE” screen messages are instead likely due to variation in the breath exhalation pattern of the drinking driver. Therefore, a mandatory 15 to 20 minute wait period following every occurrence of an “INVALID SAMPLE” message is not required, but only in those instances where the qualified breath technician has reasonable grounds to suspect that mouth alcohol may be a factor.