Advances in computer hardware over the past several decades have helped to expand the capabilities of boiler control systems in power generating applications. These greater capabilities have supported a proliferation of computer controlled boiler functions and, in many cases, replaced human operator functions with automated functions. Nevertheless, the human operator remains a central piece in many modern boiler control systems. One reason the operator is still present in the control room is that computer controls and human operators each have distinct advantages. Consequently, a boiler control system design should balance the best integration of automatic and operator control functions while balancing various requirements and design goals. The following question should then be answered: what roles or functions should be given to the operator vs. to the computer controls?

We will address this question by considering the guidance of relevant codes and standards, which have historically influenced control system design for large boilers in power generating applications. An analysis is performed on current and historically relevant standards and codes, including NFPA 85 and its predecessors, to consider how the guidance has changed along with control system technology. The analysis examines provisions directed toward manual and automatic controls to better understand the types of operations that are best-suited for manual functions versus automatic functions. Over time, NFPA 85 and its predecessors responded to the growing automation capabilities by requiring more automatic controls. While the emphasis placed on automatic controls for safety functions has grown, these standards suggest a balance or combination of automatic and manual controls for safety functions. These concepts are considered relative to those of Inherently Safe Design commonly applied in the chemical process industry.

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