Selected issues associated with the functional safety analysis according to the international standards IEC 61508 and IEC 61511 are presented. Determining the safety integrity level (SIL) of electric/electronic/programmable electronic (E/E/PE) safety-related systems is outlined. The importance of quantitative probabilistic modeling of these systems in verifying SIL is emphasized. Some aspects concerning the functional safety analysis of systems for detecting the combustible or toxic gases in relation to a CENELEC draft standard prEN 50402 are shortly discussed. Basic principles of methodology for the functional safety assessment of protective systems for potentially explosive atmospheres proposed in a CEN draft standard prEN 15233 are addressed. (c) 2005 Elsevier Ltd. All rights reserved.