Breath and/or blood analysis : some fundamental comments.

This paper comments on some problems arising if breath tests are made the only method for assessing driving under the influence of alcohol. Considerable confusion arises, because the few European countries that have introduced evidential breath testing have various basic assumptions and different cut-off levels for determining when a driver is considered to be under the influence of alcohol. Thus the author strongly recommends using the term `breath alcohol concentration' (`BrAC') if the alcohol level is measured in breath, and the term `blood alcohol concentration' (`BAC') if it is measured in blood. The assumed ratio between the two units should be specified. International agreement about a unified nomenclature and definition of BrAC and BAC, using standard units, is highly desirable. A table of legal BrAC and BAC levels in six European countries makes it clear that different values are legalised in blood and breath, because BrAC and BAC values cannot be compared directly. Thus changes in European legislation meet the logical necessity of introducing separate legal limits for BrAC and BAC. More research is needed on breathing, if breath tests are to be used as a basis for legal procedures. Blood samples will still be needed to analyse drugs, congeners and biochemical markers.