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Charles Fialkowski |

Separation requirements for your BMS at sites with mulitple boilers?

For years, I have always driven for complete seperation and independence for all PLC based burner management systems (BMS) as per my own personal interpetation (per NFPA 85 requirements).  Below is an excerpt from the current NFPA 85 standard.  I"m NOT talking about seperation between the control layer and the safety layer, rather, what to do when your plant has multiple boilers on site? 

 4.11.7* Requirement for Independence. Except as noted in, the burner management
system shall be provided with independent logic, independent
logic solving hardware, independent input/output systems,
and independent power supplies and shall be a device functionally
and physically separate from other logic systems

I was starting to question my own interpertation as beeing possibly too conservative.

We have been seeing a number of plants that have MULTPLE small package boilers (single burner, single fuel), looking to upgrade their existing BMS (PLC) to utilized safety PLC technology.  The IO counts are small (less than 100), but based on the interpretation above, we continue to quote MULTIPLE SIL-rated, PLC based BMS systems to be compliant.

I posted this issue with some of my top consultants, and the responses were not very comforting?   Meaning, I didn"t receive any consistency on their interpertations/opinions either? 

I"d be interested in what others are considering when they are looking at updating their automation for multiple units?

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