Paul Gruhn

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Paul Gruhn is a Global Functional Safety Consultant with aeSolutions in Houston, Texas. Paul is an ISA Fellow, a member of the ISA 84 standard committee (on safety instrumented systems), the developer and instructor of ISA courses on safety systems, the author of two ISA textbooks, two chapters in other books, and over two dozen published articles, and the developer of the first commercial safety system software modeling program. Paul has a B.S. degree in Mechanical Engineering from Illinois Institute of Technology, is a licensed Professional Engineer (PE) in Texas, and both a Certified Functional Safety Expert (CFSE) and an ISA 84 Safety Instrumented Systems Expert. Paul’s hobbies include home brewing, golf, painting, guitar, and reading.

Posts by Paul Gruhn:

January 28, 2020

Part 2: the use of Bayesian networks in functional safety

Past performance is not an indicator of future performance, especially for rare events. Past performance would not have indicated (at least not to those involved at the time) what would happen at Bhopal, Texas City, or any other accident you can think of. So, what is the definition of a safe plant? Some have responded, […]

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January 21, 2020

The use of Bayesian Networks in Functional Safety

Functional safety engineers follow the ISA/IEC 61511 standard and perform calculations based on random hardware failures. These result in very low failure probabilities, which are then combined with similarly low failure probabilities for other safety layers, to show that the overall probability of an accident is extremely low (e.g., 1E-5/yr). Unfortunately, such numbers are based […]

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November 22, 2019

Be careful when deep-frying a turkey!

Did you know?  Thanksgiving is the leading day of the year for home fires involving cooking equipment.   Thanksgiving is almost upon us. While deep-fried turkey is delicious (I’ve had it, but didn’t make it myself), please be aware of the risks. Deep-frying a turkey can be very dangerous as they have a high risk […]

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September 5, 2019

SIL ratings and certification for fire & gas system hardware; Is industry barking up the wrong tree?

There are many devices (sensors, logic solvers and final elements) used in safety instrumented systems that are independently certified for use in safety applications to different safety integrity levels (SIL). There is considerable debate however whether fire and gas system hardware should have SIL ratings at all. Vendors are naturally interested in promoting independently certified […]

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December 20, 2018

Process Safety Management, Jenga, Drift, and Preventing Process Industry Accidents

Blog by Paul Gruhn, P.E., CFSE, Global Functional Safety Consultant, aeSolutions       Have we really learned anything from previous accidents? There have been many well publicized process industry accidents over the last several decades. Articles and books have been written about many of these events. However, most books essentially reviewed what happened the […]

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White Papers by Paul Gruhn:

The use of Bayesian Networks in Functional Safety

Functional safety engineers follow the ISA/IEC 61511 standard and perform calculations based on random hardware failures. These result in very low failure probabilities, which are then combined with similarly low failure probabilities for other safety layers, to show that the overall probability of an accident is extremely low (e.g., 1E-5/yr). Unfortunately, such numbers are based on frequentist assumptions and cannot be proven. Looking at actual accidents caused by control and safety system failures shows that accidents are not caused by random hardware failures. Accidents are typically the result of steady and slow normalization of deviation (a.k.a. drift). It’s up to management to control these factors. However, Bayes theorem can be used to update our prior belief (the initial calculated failure probability) based on observing other evidence (e.g., the effectiveness of the facility’s process safety management process). The results can be dramatic.

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SIL ratings and certification for fire & gas system hardware; Is industry barking up the wrong tree

There are many devices (sensors, logic solvers and final elements) used in safety instrumented systems that are independently certified for use in safety applications to different safety integrity levels (SIL). There is considerable debate however whether fire and gas system hardware should have SIL ratings at all. Vendors are naturally interested in promoting independently certified hardware in order to differentiate their products. Considering the differences between safety instrumented systems and fire and gas systems, focusing on the SIL rating or performance of the actual fire and gas hardware alone is considered by some to be a misleading and questionable practice. This paper reviews a) the differences between safety instrumented systems and fire and gas systems, b) how typical voting of fire and gas sensors not only reduces nuisance trips (which is desirable) but also reduces the likelihood of the system actually responding to a true demand (which is not desirable), and c) why concepts and standards that apply to safety instrumented systems (e.g., SIL ratings) may not be appropriate for fire and gas systems.

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Process Safety Management, Jenga, Drift, and Preventing Process Industry Accidents

Process Safety Management, Jenga, Drift,
and Preventing Process Industry Accidents

Paul Gruhn, P.E., CFSE

Global Functional Safety Consultant

aeSolutions, Houston, TX

paul.gruhn@aesolns.com

 

Abstract

There have been many well publicized process industry accidents over the last several decades. Much has been written about them, and many lessons learned have been proposed. Yet evidence would indicate there has not been a lessening of industry accidents. More recent realization of the complexity of modern processes, and the organizations responsible for designing, building, running, and maintaining them, has resulted in a broader understanding of accident causation, and what can be done to try and prevent further incidents. This paper will review the previous thinking process and recommendations, and offer an alternative approach and recommendations.

 

 

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Burner Management System Challenges and Opportunities in Brownfield Installations

A two‐prong templatized approach to multiple brownfield burner management system upgrades can result in significant cost savings. The first step requires coming up with an equivalent design for the safety instrumented burner management system following the ISA 84 safety lifecycle, as allowed in current NFPA standards. The second step utilizes a templatization approach for multiple units with common functionality that will allow an organization to further maximize savings. Actual experience doing this on repeat BMS projects indicate the level of overall savings can be as high as 75% on the safety lifecycle, 70% on the control system design and integration, and 35% on the operation and maintenance activities. The combined overall savings are roughly 60%.

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Integrating ICS Cybersecurity and Process Safety Management (PSM)

The majority of process plants today are controlled and operated by automation systems built on Ethernet TCP/IP networks and legacy Microsoft operating systems. These systems are vulnerable to cybersecurity breaches resulting in potentially significant risks. Standards have been developed on how to assess and mitigate cyber risks to these systems. This paper provides an introductory summary of these topics.

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