LOPA misapplied: Common errors can lead to incorrect conclusions

Layer of protection analysis (LOPA) has quickly gained acceptance in the chemical processing industries and has risen to be one of the leading risk assessment techniques used for process safety studies. LOPA generally uses more rigor and science than what is encountered with qualitative risk assessments, while still not becoming overly onerous when compared with detailed quantitative risk assessments. In the interest of balancing time and resources against science and accuracy, certain tradeoffs and assumptions are made within the LOPA assessment. In turn, these tradeoffs and assumptions can lead to inaccurate conclusions. For example, one issue that arises is with the treatment of protection layers associated with mitigation of consequences. LOPA teams have a choice to account for mitigation layers in the consequence assignment or alternatively treat these layers as independent protection layers (IPLs). Although this may appear to be an inconsequential decision, it can in fact result in very different conclusions. In the course of treating mitigation layers as IPLs, organizations must ensure the necessary inspection, testing, and preventive maintenance practices are in place for these layers. Furthermore, recognizing this dichotomy in treatment, one can also show that these mitigation layers should be designed so as to achieve a balance between consequence reduction and desired reliability. This article discusses alternative treatments of risk mitigation layers that are commonly applied by LOPA teams and demonstrates their impacts through case studies. © 2011 American Institute of Chemical Engineers Process Saf Prog, 2011

Section: Discussionmentioning

confidence: 99%

LOPA onions: Peeling back the outer layers

Wasileski¹,

Henselwood

2011

“…More details of this specific book [5] description are found in a 2009 Loss Prevention Symposium Proceedings [6]. There are additional articles that contain background information that will help with the application of LOPA risk assessment methods [7–9].…”

Section: Discussionmentioning

confidence: 99%

Initiating events and independent protection layers

Murphy¹,

Chastain

Bridges³

2009

Layer of protection analysis (LOPA) is a semiquantitative tool for analyzing and assessing process risk. The tool has grown greatly in popularity and usefulness since the publication of the first CCPS/AIChE guidebook on the subject, Layer of Protection Analysis, Simplified Process Risk Assessment (LOPA). This article is a summary of a new CCPS guideline book that includes the following: Initiating events (IEs). Independent protection layers (IPLs). Criteria for identifying the value of each prospective IE and prospective IPL. Example IE and IPL data. This book is a necessary reference for those applying the LOPA methodology. © 2009 American Institute of Chemical Engineers Process Saf Prog, 2009

“…This particular article is a summary of a paper in the AIChE's Loss Preventions Symposium Proceedings [3]. Process Safety Progress has additional LOPA articles [4–6] to assist the practicing engineers to appropriately use this important risk reduction tool.…”

Section: Discussionmentioning

confidence: 99%

LOPA as practiced at a global manufacturing API facility

Evenson

Befus

Dolfi

et al. 2009

The standard risk assessment practices used in industry since the OSHA 1910.119 regulation was issued, are to conduct Process Hazard Analyses (PHAs) for hazardous and exothermic (or otherwise high risk) processes. During PHAs, the potential consequences of an undesired event are evaluated along with the safeguards that exist to mitigate the consequences or reduce the frequency of the event. If the PHA team determines that the risk is still not tolerable, additional safeguards are recommended to reach a tolerable level of risk. Typically, a Quantitative Risk Assessment can be completed to evaluate the effectiveness of these existing or newly proposed safeguards. Unfortunately, this is a complex and time‐consuming task. The relatively new methodology of Layer of Protection Analysis (LOPA) allows a PHA team to evaluate the effectiveness of safeguards in reducing risk in an efficient yet semiquantitative fashion using some basic assumptions and standard lookup tables. The LOPA methodology can be utilized to evaluate the effectiveness of Safety Instrumented Functions (SIF) (e.g., automated critical interlocks and alarms) to achieve a tolerable risk. The LOPA methodology provides consistency in an approach to risk assessments and communications. It can support an effective mechanical integrity or risk‐based maintenance system for critical components of an SIF. This article describes LOPA and includes several scenarios that will provide an overview of how the LOPA methodology is used in a multibatch pharmaceutical facility. © 2009 American Institute of Chemical Engineers Process Saf Prog, 2009