For a possibility of using the safety relevant system in practice, it is necessary to prove, that safety requirements, which are defined based on results of risk analysis, are fulfilled. Part of proving the safety of safety relevant system is also quantitative evaluation of safety integrity of the hardware which is involved in the safety functions realization. Objective of the paper is to compare different ways of the quantitative hardware safety integrity evaluation. For a specific technological process are identified hazards, their consequences and from them resulting safety functions. For each defined safety function is, by three different procedures, calculated the probability of dangerous failure per hour. At the end of the paper are stated reasons of results mismatch, which were obtained using different approaches.