The evaluation of new evidential breath testing instruments in the UK is planned to begin early in 1993. The preparation and content of their "Guide to Type Approval" document is reviewed in the light of the last nine years' experience. The work done and the problems of producing a formal document are discussed. A working group was formed in 1988 under the International Organisation of Legal Metrology (OIML), to consider drafting an international specification for new evidential breath testing instruments. Its 1989 recommendations have remained at the draft stage. Research has been conducted at the Central Research and Support Establishment (CRSE) of the UK's Forensic Science Service, into: breath differences, failure to provide a statutory breath sample, and possible substances interfering with breath tests. The Guide has an introduction, followed by chapters on: type approval procedure, general requirements, definitions, general technical specification, and metrological characteristics. Its annexes specify test schemes for instrument response to: chemical interference, physical interference, and alcohol vapour samples. A decision was also taken to replace existing liquid simulators by gas simulators.
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