Dominika Jama

The aim of the study was to determine the components of measurement uncertainty in the concentration of alcohol in exhaled breath and to determine the state of sobriety at the time of incident. Based on the literature review and the authors’ experience in providing opinions for law enforcement and the judiciary, the influence of various factors on the final interpretation of sobriety state is described on the basis of measurement uncertainty of breath analyzers, uncertainty of retrospective and prospective calculations, and uncertainty related to the conversion of alcohol concentrations detected during breath and blood tests. The paper pays particular attention to interpreting the concentrations of ethanol in exhaled breath close to the legal limits of the state of sobriety and the state after alcohol use, or the state after alcohol use and the state of insobriety.

Analyzing the results of an exhaled breath test concerning concentrations close to the values of 0.1 mg/dm3 and 0.25 mg/dm3, it is necessary to take into account the factors affecting the measurements obtained, including the measurement uncertainty of the determination of alcohol in exhaled breath, the processes of absorption, distribution and metabolism of ethyl alcohol, and the possibility of the presence of alcohol lingering in the oral cavity. The incorrect execution of measurements of the tested person’s alcohol concentration is also a problematic issue. When determining sobriety state by means of retrospective and prospective calculations, it is important to remember that the uncertainty of the result is affected by a number of factors and depends, among other things, on the information provided by the suspect. Hence, the expert should draw conclusions particularly cautiously and any overestimation or underestimation of the components of uncertainty can lead to erroneous conclusions. Awareness of the uncertainties inherent in the results of a sobriety test or alcohol calculation allows for meaningful interpretation of test results and determination of the sobriety state of the person tested.

In cases requiring determination of the ethanol content of a person involved in a road incident, expert opinions are often based on prospective calculations. Declarations regarding the amount and type of alcoholic drink consumed are used to calculate the concentration of alcohol in the body and to correlate the results obtained with those of sobriety tests. alcohol concentration estimated using a prospective calculation should correspond most accurately with the ethanol content in the body. It is therefore desirable to identify the appropriate model of prospective estimation, which is accomplished here by comparing the most common methods of alcohol calculation used by forensic experts. The study involved five people aged 29–64 (two women and three men) who were given alcohol in an amount leading to a theoretical ethanol concentration of 1‰in their bodies. In this paper, we plotted the alcohol curves and compared the experimental (real) ethanol concentration with the theoretical values calculated by the various methods. The best correlation between the results of prospective calculations and real ethanol concentrations was obtained for the method that assumes an immediate elimination from the beginning of consumption (used routinely by the authors) and for the method that assumes an absorption time of 30 minutes and a 10% alcohol deficit (the difference between the theoretical and actual ethanol concentration).