A functional safety assessment methodology for explosion protection with application to a variable frequency drive system

Abstract

Modern explosion protection equipment, protected by traditional explosion protection technology (as defined by the international electrotechnical commission (IEC) publication IEC60079-ff series standards) and electrical/electronic/programmable electronic (E/E/PE) safety-related systems, is becoming ever more complex in coal mine development and petrochemical industry; thus, the possibility of failures in their operation is also growing. It is well-known that E/E/PE safety-related systems can be used to actively control dangerous sources, with real and expected levels of reliability, if they have been qualified according to the IEC61508-ff series standards. To uniformly evaluate the safety integrity level (SIL) of the explosion protection function of traditional explosion protection technology and E/E/PE safety-related system technology, this study analyzed the ability of these types of protection to remove the ignition risk residual, evaluating the failure rates of safety devices. The key objective of this paper is the presentation of a new equipment protection level (EPL) assessment method for explosion protection equipment based on a functional safety assessment. The method is applied to a variable frequency drive (VFD) system, and the results show that the EPL of the explosion protection equipment evaluated by this method is consistent with the EPL corresponding to the traditional explosion protection type of the IEC60079-ff series standard. Meanwhile, the flexible configuration of explosion protection safety devices and E/E/PE safety-related systems enables explosion protection equipment of different EPL levels to be designed.