Programmable electronic and hardwired emergency shutdown systems: a quantified safety analysis.
IAS '05: Conference Record of the 2005 IEEE Industry Applications Conference: Fortieth IAS Annual Meeting, October 2-6, 2005, Kowloon, Hong Kong. Piscataway, NJ: Institute of Electrical and Electronics Engineers, 2005 Oct; 1:210-217
Emergency shutdown systems (ESDs) for mining machinery provide critical functions to safeguard miners. Traditionally, ESDs were realized with simple hard-wired circuits. Today, there is a growing trend to use programmable electronic technology such as programmable logic controllers (PLCs). This paper describes an analytical study to quantify the safety integrity of a PLC-based ESD and a hard-wired ESD. The safety integrity level of each design approach was determined by quantifying the average probability of failure on demand as described by the recommendations for programmable electronic mining systems published by NIOSH and the International Electrotechnical Commission (IEC) 61508 standard. The safety analyses addressed system architecture, hardware failure probability, proof test interval, diagnostic coverage, and human error probability. The results showed that a same level of safety, safety integrity level 3 (SIL 3), could be attained when evaluating random hardware failures. Neither approach could attain SIL 3 if manual activation was used. It is apparent that automatic versus human activation of the ESD is a very important safety consideration. Manually actuated ESDs can only achieve SIL 1 regardless of the technology; therefore, additional independent safety layers of protection are needed to exceed SIL 1. Secondly, it is apparent that the technology choice is very important. The PLC-based ESD was much simpler to design.
Electronic-equipment; Miners; Safety-research; Hazards; Injuries; Injury-prevention; Mining-industry; Mining-equipment; Electronic-devices
NIOSH Pittsburgh Research Laboratory, P.O. Box 18070, Pittsburgh, PA 15236
IAS '05: Conference Record of the 2005 IEEE Industry Applications Conference: Fortieth IAS Annual Meeting, October 2-6, 2005, Kowloon, Hong Kong