. "4 Identification and Use of Process Safety Metrics." Assessment of Approaches for Using Process Safety Metrics at the Blue Grass and Pueblo Chemical Agent Destruction Pilot Plants. Washington, DC: The National Academies Press, 2011.
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Assessment of Approaches for Using Process Safety Metrics at the Blue Grass and Pueblo Chemical Agent Destruction Pilot Plants
Administration’s (OSHA’s) injury/illness metric, which has been utilized broadly to benchmark worker safety performance. Another aim of the project was to identify leading metrics that would monitor management systems or other early indicators of necessary actions that had to be taken to avoid process safety incidents, especially catastrophic incidents such as those at Union Carbide in Bhopal, India; BP in Texas City, Texas; and Phillips in Pasadena, California.
Industry interest and participation in the CCPS Metrics Project grew with the release of The Report of theBP U.S. Refineries Independent Safety Review Panel (also known as the Baker panel) and the U.S. Chemical Safety Board’s (CSB’s) Investigation Report: RefineryExplosion and Fire, Report No. 2005-04-I-TX, following the incident at the BP Texas City refinery in 2005. Both reports called upon industry to develop and implement better leading and lagging metrics. The CCPS Metrics Project resulted in two publications, a process safety metric pamphlet in December 2007 that recommended specific metrics for industry benchmarking3 and a book in 2009 titled Guidelines for Process SafetyMetrics. The latter document recommended a process for companies to adhere to in selecting and implementing other metrics appropriate for their facilities.4 The metrics in the CCPS publications were embraced by many U.S. and international trade associations and became the basis for metrics collected by those organizations. These publications also describe a hierarchy of metrics, both lagging and leading. Lagging metrics relate to events that actually occurred (e.g., unintended releases of chemicals). Leading metrics may include near-miss events that did not result in an unintended release, management system failures (e.g., missed or overdue inspections), activation of safety systems, or other events that might indicate areas requiring attention to reduce the likelihood of a significant event. The hierarchy is illustrated as a pyramid in Figure 4-1. There are typically more minor events than major events, more near misses than actual releases, and more management system defects or other early indicators than near misses.
The CCPS Guidelines for Process Safety Metrics expanded the discussion of metrics by describing the processes that a company or organization should use to select metrics that are specific or applicable to that organization. It also included an appendix document containing several hundred potential metric options that an organization should consider, depending upon the areas of performance that are most important or in need of strengthening for that organization.
The relationship of the hierarchy of incident categories to the James Reason barrier model is shown in Figure 4-1. The latter model illustrates independent layers of protection, which can alternatively be illustrated by the “Swiss cheese” model that is shown in Figure 4-2. As explained in the two previously noted CCPS documents, there are typically multiple independent layers, or barriers, that prevent an incident from occurring or that limit the severity of an incident. When all process safety barriers are in place, a single barrier can typically fail without significant consequences. However, when multiple barriers fail, the probability that an incident can occur is increased. Individual barrier failures may often occur without being noticed until a second or third barrier has failed. For this reason, metrics are needed to ensure the integrity of all barriers.
American Petroleum Institute Metrics
Following the completion of the CCPS Metrics Project, the CSB still desired that an American National Standards Institute (ANSI) standard be developed to codify the recommendations on process safety metrics. It hoped in this way to ensure that all relevant companies and stakeholders would support a common set of metrics. CSB requested that API work with the United Steelworkers’ Union to sponsor an ANSI standard project. A committee was organized, and an ANSI standard, Process Safety Performance Indicators for theRefining and Petrochemical Industries (ANSI/API RP 754), was created. The vast majority of definitions and concepts developed by the CCPS Metrics Project were retained in the ANSI/API RP 754 document.5 Since this document was developed shortly after issuance of the original CCPS metric definitions, the API committee used the opportunity to make minor modifications to metric definitions based upon lessons learned from early implementation by users of the original CCPS metrics. See Box 4-1 for definitions of Tier 1-4 process safety events from API RP 754.