The subject of the final paper is the study of how an accredited institution working with the norms as the law functions. The research was carried out in the company of the Institute for Research and Development of Security d.o.o. which is for testing according to norms. The first part describes what requirements are covered by ISO/IEC 17025, while in the second part of the final work it is described technically process for causing and analyzing waste gases from small combustion devices. From this one practical test, there are apparent requirements that must be covered in order to carry out an adequate examination.