Functional Safety, a SIF-Based Approach, and Burner Management

Earlier this week, Emerson’s Chuck Miller and Mike Boudreaux were at the ChemInnovations 2010 conference in Houston, Texas. During this session, presenters talked about topics related to safety and security for instrumentation, automation, and control in the chemical and petrochemical process industries. Chuck reported on the process safety system presentations that covered a wide variety of topics including the basics of functional safety in the chemical process industry, the importance of a SIF-based approach to functional safety, and the application of standards to burner management systems.

Here’s his report:

Mike’s presentation was on The IEC 61511 / ISA 84 Approach to Functional Safety. He shared how IEC 61511 and ISA 84, the modern functional safety standards for the process industries, are based on the concept of a safety instrumented function (SIF). Considering safety functions independently from each other isn’t all that new, but taking a SIF-based approach to functional safety lifecycle management provides key benefits in the analysis, implementation, and operation phases of a safety instrumented system (SIS). The IEC 61511 approach enables more practical safety lifecycle management, ensuring that just the right amount of technology, complexity, and effort is applied where it is needed. The result of this kind of approach is optimal process reliability, flexibility to meet project needs, reduced engineering and complexity, and easier regulatory compliance.

Regulatory compliance is a necessary objective, but the end goal of a process safety system is to provide process safety. To simply meet regulatory compliance does not always deliver a safe process. A safety system should provide protection against equipment failures as well as systematic failures that can only be prevented by an adequately functioning safety lifecycle management system. Policies, procedures, and other management systems need to be in place to prevent systematic failures from being introduced into the system well after the system is designed, installed, and validated.

This is why safety lifecycle management is an important aspect of IEC 61511. Engineers who are focused on the equipment design considerations such as technology selection and component subsystem architectures sometimes overlook it. A process safety system needs to stand the test of time, and safety lifecycle management is the best way to ensure that this happens.

Another important topic that was discussed was the incorporation of performance and prescriptive-based standards for burner management systems (BMS). Charlie Fialkowski, the author of the Siemens Process Safety USA blog, presented on this topic, and explained the reasons why a BMS should be considered an SIS and how prescriptive standards such as NFPA 85 should be considered as complimentary to performance standards such as IEC 61511 and ANSI/ISA 84. I recently presented very similar concepts in a presentation at Emerson Exchange titled What Now? More Standards for Safety and Regulatory Compliance.

In his presentation, Mr. Fialkowski explained that prescriptive standards detail how to implement an application for combustion process by specifying “what and how to” monitor specific conditions, perform diagnostics, and maintain fault tolerances and redundancy levels. Whereas performance-based standards tell us “how well” to adequately design a safety system by effectively quantifying performance, risk reduction levels, and device failure rates. The key point is that performance-based standards tell us how well we must implement the prescriptive standards. Both types of standards are important in BMS design. With the guidance provided by ISA-TR84.00.05, recommendations on the identification of safety instrumented functions in burner management systems, the performance and prescriptive standards can now be more easily tied together.

According to the ISA website, ISA-TR84.00.05 is intended to identify and classify SIFs within typical BMSs for typical operating modes of fired equipment (e.g., pre-firing, light-off, shutdown, and normal operation) and to provide examples of typical safety assessments for boilers (single burner), fired process heaters (multi-burner), thermal oxidizers, oil heater treaters and glycol reboilers that use a BMS.

Interest in process safety best practices among the chemical and petrochemical manufacturers at ChemInnovations 2010 was quite high. Chuck will continue to share some of these best practices at two upcoming Safety Lifecycle seminars in Chicago (Oct 26) and Minneapolis (Oct 28).

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