Download Guidelines for Enabling Conditions and Conditional Modifiers by CCPS (Center for Chemical Process Safety) PDF

By CCPS (Center for Chemical Process Safety)

The preliminary Layer of security research (LOPA) publication released in 2001 set the principles and techniques for utilizing LOPA as an intermediate approach among in basic terms qualitative risks evaluation/analysis and extra quantitative research tools. uncomplicated LOPA offers an order-of-magnitude probability estimate of hazard with rather reproducible effects. LOPA effects are thought of serious in opting for protection integrity point for layout of protection instrumented platforms.

This guide clarifies key techniques and reinforces the constraints and the necessities of LOPA. the most scope of the rule of thumb is to supply examples of CMs and ECs and to supply concrete suggestions at the protocols that has to be to exploit those options. The book presents a short evaluate of Layer of safeguard research (LOPA) and its adaptations, and summarizes terminology used for comparing situations within the context of a regular incident series. It defines and illustrates the most typical kinds of ECs and CMs and exhibits how they interrelate to threat standards in addition to their program to different methods.

Chapter 1 Context (pages 1–22):
Chapter 2 Lopa allowing stipulations (pages 23–36):
Chapter three Lopa Conditional Modifiers (pages 37–69):
Chapter four program to different tools (pages 71–80):

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Extra info for Guidelines for Enabling Conditions and Conditional Modifiers in Layer of Protection Analysis

Example text

Calculate the expected indoor concentration based on pertinent factors such as the building air exchange rate, then compare the calculated indoor concentration to the threshold or other toxic effect level used. This approach recognizes that the indoor concentration is often considerably less than outside the building, particularly for short-duration releases. Some dispersion modeling software packages such as ALOHA® (EPA 2012) include routines for evaluating indoor concentrations of toxic materials that are exposed to an external toxic cloud.

The use of enabling conditions and conditional modifiers falls into this realm. Description LOPA is typically applied after, and builds upon, the information gathered in a qualitative hazard evaluation, but can be applied to scenarios gathered from any source, such as an audit or incident investigation. LOPA, in turn, can be used as a screening tool for scenarios prior to application of a full quantitative risk analysis. 2). After the scope of the study is defined, LOPA consists of the six steps summarized below.

Caution must be exercised when evaluating seasonal risk scenarios due to the possibility of common mode failures between the enabling condition and an independent protection layer. True independence is needed for a time-at-risk enabling condition. The following examples illustrate possible common-mode situations: • • • A low-temperature condition both allowing an abnormal situation to develop and causing failure of a protective system due to instrumentation freeze-up. A rainstorm both enabling an operational error to occur due to poor visibility and contributing to an ensuing release by secondary containment overflow.

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