19 June 2018

Are you prepared for the new independence rules for BMS designs?

On December 1, 2014, the 2015 edition of the National Fire Protection Association (NFPA) 85, Boiler and Combustion Systems Hazards Code was approved as an American National Standard. The scope and purpose of the NFPA 85 committee, as well as its six technical sub-committees, is to establish the minimum requirements for: design safety, installation, operation, maintenance, and training for all types of boilers including single and multiple burners, stokers, fluidized bed and heat recovery steam generators (HRSGs).

The boiler industry generally uses two or more control systems to provide proper control and safe operation. The combustion control system (CCS) manages the regulatory control functions (feedwater control, air and fuel control, etc.) and the burner management system (BMS), which provides safety control for the operation to start and stop the fuel.

NFPA 85 has a long history of prescribing specific requirements for programmable logic controllers (PLCs) that are used as the BMS. In fact, entire sections in the standard have been dedicated to describe what needs to be implemented in a modern day BMS. One of NFPA’s most notable and argued requirements is their long-standing position on BMS independence.

What is the requirement for BMS independence?

According to the NFPA 85, the requirement for BMS independence states that:

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.

The committee has defended their position with explanatory information for system independence to:

This requirement has been published for over 20 years in the NFPA Standards. However, recently one of the sub-committees for single burner boilers has introduced a new condition that is geared to combining systems.

To learn more about Siemens Burner Management Systems, please click here.

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