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Schmidt M.S.,Bluefield Process Safety LLC | Schmidt M.S.,Missouri University of Science and Technology
Journal of Loss Prevention in the Process Industries | Year: 2014

When a team is analyzing a LOPA scenario, the team needs to consider all three roles played by human interaction in the scenario: that of cause, as a result of human error; that of receptor, both in terms of safety impacts (inside the fence line) and community impacts (outside the fence line); and that of independent layer of protection (IPL), considering both administrative controls and human responses. Frequently, the nature of these three roles are inter-related, and setting guidance that is internally consistent is important to using LOPA to assess risk rather than as a means to game the analyses to simply achieve a wished-for result.A number of criteria have been proposed to quantify human involvement, typically as cause, as receptor, or as IPL. Establishing a framework to look at all three in a unified way is more likely to result in analyses that are consistent from scenario to scenario.This paper describes such a framework and presents it in a way that allows organizations to review their own criteria for quantifying human involvement in LOPA. It also examines some of the published LOPA criteria for human involvement and looks at them in terms of consistency of approach between evaluation of cause, receptor, and IPL. Finally the paper makes suggestions to use in calibrating LOPA methodologies to achieve consistent and believable results in terms of human interaction within and between scenarios that have worked for other organizations. © 2013.


Schmidt M.S.,Bluefield Process Safety LLC
50th Annual Loss Prevention Symposium 2016, LPS 2016 - Topical Conference at the 2016 AIChE Spring Meeting and 12th Global Congress on Process Safety | Year: 2016

Most of the literature on catastrophic failures of low pressure tanks focuses on the ignition of explosive mixtures in the vapor space of those tanks, and rightly so, because most catastrophic failures of atmospheric tanks involve explosions of such mixtures. Moreover, there is a general sense in the industry that other than explosions of flammable mixtures, the only other hazard associated with low pressure tanks is the occasional dramatic implosion of a vessel that is inadequately protected against vacuum. In fact, there are a number of mechanisms that can lead to the catastrophic failure of a low pressure tank that have nothing to do with combustion or unprotected vacuum. Under certain circumstances, even a tank equipped with an atmospheric vent and containing nothing other than salt water can explode, with disastrous impacts. This paper reviews the mechanisms for catastrophic failure of low pressure tanks, both implosion and explosion, and serves as a reminder for experienced process safety practitioners and as a tutorial for new process safety practitioners of what to look for during a hazard review. It also includes a case study of an atmospheric caustic tank explosion that resulted from a previously unreported mechanism that involved neither combustion nor vacuum. © 2016, Smith & Burgess, LLC.


Schmidt M.S.,Bluefield Process Safety LLC | Kilpatrick D.,CF Industries Inc.
11AIChE - 2011 AIChE Spring Meeting and 7th Global Congress on Process Safety, Conference Proceedings | Year: 2011

Terra Industries operated several nitrogen products facilities before being acquired by CF Industries. Each of these facilities had units that convert natural gas and air to ammonia and from that ammonia produced upgrade products, e.g., urea and ammonium nitrate (AN). Two plants operated by Terra Industries had identical AN solution pump installations. However, the teams performing the Layer of Protection Analysis (LOPA) concluded that the safety instrumented functions to protect those pumps needed different safety integrity levels (SIL). They discovered differences that warranted different conclusions about what SIL assignment should be. A discussion on the consequences of AN pump hazards covers the use of LOPA for SIL assignment; causes of AN hazards; types of independent layers of protection; the impact of risk tolerance criteria, frequency modifiers, and IPL on final SIL assignment; and reasons why dictating a fixed SIL assignment to certain types of hazards or installations is inappropriate, particularly in the development of industry standards or government regulations. This is an abstract of a paper presented at the 2011 AIChE Spring Meeting & 7th Global Congress on Process Safety (Chicago, IL 3/13-17/2011).


Sellers A.J.,Bluefield Process Safety LLC | Schmidt M.S.,Bluefield Process Safety LLC
16th Process Plant Safety Symposium 2014, PPSS 2014 - Topical Conference at the 2014 AIChE Spring Meeting and 10th Global Congress on Process Safety | Year: 2014

The three criteria for an independent layer of protection (IPL) are effectiveness, independence, and auditability. The effectiveness and independence of an IPL typically are evaluated as part of a Layer of Protection Analysis (LOPA), and normally are confirmed by the time the LOPA is finalized. Auditability, on the other hand, is typically not addressed during the LOPA, and frequently is not addressed until someone is charged with the task of actually auditing the IPL, assuming that even occurs. For a Safety Instrumented Function (SIF) with a Safety Integrity Level to be installed in a Safety Instrumented System (SIS), the requirements for auditing are listed in the standards such as IEC 61511 and ANSI/ISA S84 and the relevant information is contained in a Safety Requirements Specification (SRS). However, an SRS for an SIS does not address IPLs that are not SIFs: administrative functions, non-instrumented functions, and non-rated control functions, even though they are also critical to assuring sufficient risk reduction for specific hazards. The auditability, and hence the auditing, of IPLs not installed in an SIS too often becomes an afterthought. A Safety Critical Functions Manual (SCFM) can pick up where the SRS leaves off. It defines requirements for testing, maintenance, and training for IPLs not included in the SIS. The very act of creating an SCFM forces the issue of auditability to be addressed, and defines the items that need to be audited. While an SCFM could manifest itself in different ways, it generally can be expected to include datasheets which address the operation, testing, maintenance, and training requirements for each safety critical function. Although it would be analogous to an SRS, an SCFM typically would be simpler. The paper includes a discussion of an approach to SCFMs that has been successful at a number of different organizations for documenting and maintaining those safety critical IPLs that are not already covered by one of the SIS standards.


Schmidt M.S.,Bluefield Process Safety LLC | Kilpatrick D.,CF Industries Inc.
Process Safety Progress | Year: 2012

Two plants operated by the same company have "identical" ammonium nitrate (AN) solution pump installations. Yet the teams performing the layer of protection analysis (LOPA) concluded that the safety instrumented functions (SIFs) to protect those pumps needed different safety integrity levels (SILs). Despite the similarity of the installations, the teams discovered legitimate differences that warranted different conclusions about what SIL assignment should be. For those with a specific interest in AN, this article reviews the consequences of AN pump hazards, their initiating causes, and the types of independent layers of protection (IPLs) that can be brought to bear. Of more general interest will be the discussion of the impact of risk tolerance criteria, frequency modifiers, and IPLs on final SIL assignment, and why dictating a fixed SIL assignment to certain types of hazards or installations is inappropriate, especially in the development of industry standards or government regulations. © 2012 American Institute of Chemical Engineers (AIChE).

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