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Process Safety and Instrumentation

This chapter discusses instrumentation issues related to industrial process safety. Instrumentation safety may be broadly divided into two categories: how instruments themselves may pose a safety hazard (electrical signals possibly igniting hazardous atmospheres), and how instruments and control systems may be configured to detect unsafe process conditions and automatically shut an unsafe process down.

In either case, the intent of this chapter is to help define and teach how to mitigate hazards encountered in certain instrumented processes. I purposely use the word “mitigate” rather than “eliminate” because the complete elimination of all risk is an impossibility. Despite our best efforts and intentions, no one can absolutely eliminate all dangers from industrial processes1. What we can do, though, is significantly reduce those risks to the point they begin to approach the low level of “background” risks we all face in daily life, and that is no small achievement.


Classified Areas and Electrical Safety Measures

   Classified Area Taxonomy

   Explosive Limits

   Protective Measures


Concepts of Probability and Reliability

   Mathematical Probability

   Laws of Probability

   Practical Measures of Reliability


High-Reliability Systems

   Design and Selection for Reliability

   Preventive Maintenance

   Component De-Rating

   Redundant Components

   Proof Tests and Self-Diagnostics


Safety Instrumented Functions and Systems

   SIS Sensors

   SIS Controllers (Logic Solvers)

   SIS Final Control Elements

   Safety Integrity Levels

   SIS Example: Burner Management Systems

   SIS Example: Water Treatment Oxygen Purge System

   SIS Example: Nuclear Reactor Scram Controls




Adamski, Robert S., Design Critical Control or Emergency Shut Down Systems for Safety AND Reliability, Revision 2, Premier Consulting Services, Irvine, CA.

ANSI/ISA-84.00.01-2004 Part 1 (IEC 61151-1 Mod), “Functional Safety: Safety Instrumented Systems for the Process Industry Sector – Part 1: Framework, Definitions, System, Hardware and Software Requirements”, ISA, Research Triangle Park, NC, 2004.

ANSI/ISA-84.00.01-2004 Part 2 (IEC 61151-2 Mod), “Functional Safety: Safety Instrumented Systems for the Process Industry Sector – Part 2: Guidelines for the Application of ANSI/ISA-84.00.01-2004 Part 1 (IEC 61151-1 Mod)”, ISA, Research Triangle Park, NC, 2004.

Bazovsky, Igor, Reliability Theory and Practice, Prentice-Hall, Inc., Englewood Cliffs, NJ, 1961. “Engineer’s Guide”, Pepperl+Fuchs.

“Failure Mode / Mechanism Distributions” (FMD-97), Reliability Analysis Center, Rome, NY, 1997.

Grebe, John and Goble, William, Failure Modes, Effects and Diagnostic Analysis; Project: 3051C Pressure Transmitter, Report number Ros 03/10-11 R100, L.L.C., 2003.

Hattwig, Martin, and Steen, Henrikus, Handbook of Explosion Prevention and Protection, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, Germany, 2004.

Hicks, Tyler G., Standard Handbook of Engineering Calculations, McGraw-Hill Book Company, New York, NY, 1972.

“IEC 61508 Frequently Asked Questions”,

Rosemount website, updated December 1, 2003.

Lipt´ak, B´ela G., Instrument Engineers’ Handbook – Process Measurement and Analysis Volume I, Fourth Edition, CRC Press, New York, NY, 2003.

Lipt´ak, B´ela G., Instrument Engineers’ Handbook – Process Control Volume II, Third Edition, CRC Press, Boca Raton, FL, 1999.

Lipt´ak, B´ela G., Instrument Engineers’ Handbook – Process Software and Digital Networks, Third Edition, CRC Press, New York, NY, 2002.

“Modern Instrumentation and Control for Nuclear Power Plants: A Guidebook”, Technical Reports Series No. 387, International Atomic Energy Agency (IAEA), Vienna, 2009.

Newnham, Roger and Chau, Paul, “Safety Controls and Burner Management Systems (BMS) on Direct-Fired Multiple Burner Heaters”, Born Heaters Canada Ltd.

“NFPA 70”, National Electrical Code, 2008 Edition, National Fire Protection Association.

“NIOSH Pocket Guide to Chemical Hazards”, DHHS (NIOSH) publication # 2005-149, Department of Health and Human Services (DHHS), Centers for Disease Control and Prevention (CDC), National Institute for Occupational Safety and Health (NIOSH), Cincinnati, OH, September 2005.

Perrow, Charles, Normal Accidents: living with high-risk technologies, Princeton University Press, Princeton, NJ, 1999.

Rogovin, Mitchell and Frampton, George T. Jr., Three Mile Island Volume I, A Report to the Commissioners and to the Public, Nuclear Regulatory Commission Special Inquiry Group, Washington DC, 1980.

Schultz, M. A., Control of Nuclear Reactors and Power Plants, McGraw-Hill Book Company, New York, NY, 1955.

Showers, Glenn M., “Preventive Maintenance for Burner-Management Systems”, HPAC –Heating/Piping/Air Conditioning Engineering, February 2000.

Svacina, Bob, and Larson, Brad, Understanding Hazardous Area Sensing, TURCK, Inc., Minneapolis, MN, 2001.

“The SPEC 200 Concept”, Technical Information document TI 200-100, The Foxboro Company, Foxboro, MA, 1972.

Wehrs, Dave, “Detection of Plugged Impulse Lines Using Statistical Process Monitoring Technology”, Emerson Process Management, Rosemount Inc., Chanhassen, MN, December 2006.

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