The latest 2015 editions of NFPA 85, 86 and 87 partially invoke the concepts of a Safety Instrumented System as defined by ISA S84 / IEC 61511. In the US, these standards / codes cover the majority of installed Burner Management Systems (BMS) associated with boilers, HRSGs, dryers, ovens, fluid heaters, incinerators, thermal oxidizers, etc.
The issue at hand is the concept of partially invoking the safety lifecycle. NFPA 85, 86 and 87 are attempting to mandate the use of safety PLCs as one type of acceptable logic solver for the BMS. For the process industries, this is a good thing and aligned with current practices with most end users. That said, NFPA 85, 86 and 87 do not want to mandate that one follow the remainder of the safety lifecycle. Given that NFPA 85, 86 and 87 also govern commercial installations (i.e. a boiler in the basement of a school or hospital) one can readily understand the reluctance to invoke a performance based design concept on an unsophisticated customer base where safety of the employee and / or public might be better suited with a prescriptive approach.
By attempting to develop and define BMS requirements that meets the needs of both user bases (commercial and process industries), NFPA 85, 86 and 87 misapplies the concepts of the safety lifecycle. Given that most fired device Original Equipment Manufacturers (OEM) have limited knowledge on application of ISA S84 / IEC 61511 and are competing in a competitive global economy where the “cheapest” fired device wins the order, NFPA 85, 86 and 87 safety PLC related concepts can be invoked in a manner that in my opinion might actually be less safe and thereby missing the entire objective.
NFPA 85, 86 and 87 safety PLC requirements for the BMS need to be revised / clarified to ensure:
- Process Industry can readily and safely apply SIS concepts
- Commercial Industry can readily and safety apply prescriptive requirements
Read my 16-page white paper recently presented at the 2016 Texas A&M University Instrumentation Symposium for the Process Industries for more about the latest updates and concerns with the NFPA standards.