Measurement apparatus intended for use in potentially explosive atmospheres in Europe, must comply with the EC Directive 94/9/EC, also known as “ATEX directive”. The conformity must be verified by a so called ATEX Certificate. In the frame of the EC-funded research project „Corrosion testing of tank ships“, AE-field tests on board large tank ships were executed. Intrinsically safe certified AE sensors were temporarily immersed through a potentially explosive atmosphere from the tank top through manholes into the liquid contents. Ship owners and involved classification societies insisted on the availability of a system certificate confirming intrinsic safety for the used sensors and isolation barriers and also for the whole installation for protection from the risk of a lightning strike into a signal cable running over deck. For this certification process, all details of installation, such as cabling, earthing, over voltage protection, etc., have been decided, explained and examined. This paper presents some basics of explosion protection with its terminology and the new “Product Family ISAFE“.