Suitability of measuring systems on the basis of direct-reading tubes for the measurement of hazardous workplace atmospheres

Measuring systems on the basis of direct-reading tubes can be used at the w orkplace to get quick information on concentrations of hazardous substances in the air. In this context, the question is raised whether or not these s ystems are sufficiently precise to provide more than a rough, more qualitat ive result, i.e. whether they could be employed to conduct measurements tha t meet the requirements for measuring methods used to check compliance with exposure limits as defined in TRGS 402 and DIN EN 482. To investigate this question, a couple of direct-reading tubes were tested under laboratory co nditions. The aim was to determine the measurement uncertainty at the begin ning and the end of a tube's working life and to analyse the effect of envi ronmental factors and disturbing components. It could be shown that only ve ry few of the tube types actually fulfil the requirements underlying exposu re measurements. The results are used to provide information on the selecti on and use of direct-reading tubes and to elaborate suggestions for a revis ion of the concerned standard DIN EN 1231.