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Understanding IPL Boundaries

机译：了解IPL界限

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Layer of protection analysis (LOPA) is a simplified risk assessment tool that has been in use for almost three decades. The technique has improved the focus on independent protection layers (IPLs) that can prevent the progression of an initiating cause to an undesired consequence (a scenario). An IPL must be capable of preventing the scenario from reaching the consequence. To execute the simplified LOPA approach, the IPL must be independent of the initiating cause and other IPLs. A potential pitfall in LOPA and in the management of IPLs identified in LOPA is misunderstanding the boundary of the IPL. For example, a pressure relief valve (PRV) is intended as an IPL to prevent the consequence of catastrophic rupture of the vessel with potential for fatality. In reality, for the PRV to prevent vessel rupture, the inlet piping from the vessel to the relief valve and the outlet piping from the relief valve to the ultimate destination must provide sufficient flow capability. The IPL boundary must include any block valves in the inlet and outlet piping, and any devices such as flame arrestors or back pressure controllers. The probability of failure on demand (PFD) must include everything in the expanded IPL boundary. If the IPL boundaries are not correctly understood, the LOPA is not correct and the organization is deluding itself on the risk reduction. In addition to being independent and effective in preventing the consequence, an IPL must also be auditable. If an IPL boundary does not include all the components to make the IPL effective, the audit (inspection and testing) program will be incomplete. The PFD of the excludedbut neededcomponents will be higher than the PFD of the same components that are audited. Narrow IPL boundaries give two problems in calculating the correct PFD: (1) Needed components are not included in the PFD calculation, and (2) The actual PFD of excluded components is higher than it would be if the components were inspected. The article provides examples and illustrations for several types of IPLs: safety instrumented functions, dikes, relief device with fire-resistant insulation and cladding on the vessel, operator response to alarm, and deflagration arrester. The article includes diagrams to illustrate the concepts. (c) 2018 American Institute of Chemical Engineers Process Saf Prog 38: e12019, 2019
机译：保护分析层（LOPA）是一种简化的风险评估工具，近三十年来。该技术在独立保护层（IPLS）上的重点改善了可以防止发起原因的进展对不期望的后果（方案）。 IPL必须能够阻止方案到达后果。要执行简化的洛卡方法，IPL必须独立于发起原因和其他IPL。 Lopa的潜在缺陷和在LoPA中鉴定的IPLS管理误解了IPL的边界。例如，减压阀（PRV）旨在作为IPL，以防止血管灾难性破裂的结果具有潜在的死亡。实际上，对于预防容器破裂的PRV，从容器到浮雕阀的入口管道和从浮雕阀到最终目的地的出口管道必须提供足够的流动能力。 IPL边界必须包括入口和出口管道中的任何块阀，以及任何诸如防火器或背压控制器的装置。按需失败（PFD）的可能性必须包括扩展IPL边界中的所有内容。如果无法理解IPL界限，则LoPA不正确，组织正在阐明风险降低。除了独立和有效地防止后果方面，IPL还必须是可审计的。如果IPL边界不包括使IPL有效的所有组件，审计（检查和测试）程序将是不完整的。 ExtudedBut所需组件的PFD将高于审计的相同组件的PFD。缩小的IPL边界在计算正确的PFD中提供两个问题：（1）所需的组件不包含在PFD计算中，并且（2）排除组件的实际PFD高于检查组件是否已检查组件。本文提供了多种IPLS的示例和插图：安全仪器功能，堤防，具有耐火绝缘和船体的浮雕装置，操作员对报警的响应和换挡避雷器。本文包括说明概念的图表。 （c）2018美国化学工程研究所工艺SAF PROG 38：E12019,2019

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