<正>Safe transport of dangerous cargoes by sea-going vessels requires more and more built-up, appropriately designed and manufactured systems of control which work in potentially explosive atmospheres. Designing, building and operation of devices in hazardous areas must be absolutely safe. Special kinds of their explosion protected realisation are intrinsically safe circuits. The paper presents, on the basis of selected examples of measurement lines, the problems connected with designing and operation of intrinsically safe circuits. Special attention is paid to the dissimilarity of these circuits in comparison to conventional solutions. The influence of Zener barrier and a galvanic separator on metrological properties of selected measurement lines is discussed. The basis of the presented paper may be found in the authors' earlier work.