Process Safety: Understand the Changes in API RP 754

The second edition of this standard on process safety performance indicators contains some important revisions

By Kelly K. Keim, ExxonMobil Research and Engineering, on behalf of the American Petroleum Institute

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In 2010, the American Petroleum Institute (API) issued “Recommended Practice (RP) 754: Process Safety Performance Indicators for the Refining and Petrochemical Industries” [1]. This standard has gained broad acceptance and use not only by the refining and petrochemical sectors in the United States but also by other sectors of the energy industry and by other process industries in the U.S. and around the globe.

The drafting committee recognized the entirely new nature of this standard and believed its use would lead to valuable insights that a second edition should reflect. So, the standard was re-opened in August 2013 after two complete years of data collection, and the committee considered a variety of revisions. Here’s a guide to changes in the second edition, which was published in April 2016 [2].

From the very beginning, committee members agreed that the standard is not broken, as demonstrated by its rapid voluntary adoption by many organizations and companies around the world. However, many ideas for potential improvements were suggested, including expansion of the standard for application to petroleum pipeline and terminal operations, retail service stations, and oil and gas drilling and production operations. These enhancements appear in the second edition; individual annexes define appropriate changes to the applicability and definitions sections of the RP tailored to those specific operations. Other recommendations for improvement spanned the desire for greater clarity in application of the standard to the many facets and nuances of process safety, additional guidance regarding identification and use of Tier 3 and 4 (Figure 1) leading indicators, more examples of process safety event (PSE) tiering to address questions brought forward in quarterly RP 754 webinars hosted by the API and American Fuels and Petrochemical Manufacturers (AFPM), and a few targeted changes to the criteria used to define Tier 1 and 2 PSEs.

Key Changes Considered

The three most-complex proposals for change subjected to formal balloting were:

1. Increasing the direct cost damage threshold for fires and explosions for Tier 1 from $25,000 to $100,000. This change was approved. Fires and explosions with direct cost damages between $25,000 and $100,000 move to Tier 2. The $2,500 threshold value for Tier 2 fires and explosions remains unchanged — so the total of events captured in Tier 1 and Tier 2 stays the same. The committee believes that changing the threshold to $100,000 places the significance of this category of PSE more on par with the other criteria for Tier 1.

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2. Use of the hazard class designations from the globally harmonized system for classification and labeling (GHS) to designate threshold release categories (TRCs) for tiering of releases by quantity released. No proposed change was more thoroughly studied or actively discussed than this one. Many of the existing TRC criteria (e.g., Tier 1 TRC 2, 3 and 4 for toxic inhalation hazards; TRC 5, 6 and 7 for flammable gases and liquids; and TRC 6 and 7 for skin corrosion) already are based upon the same criteria used in GHS. Criteria for other health hazards such as oral ingestion toxicity, respiratory and skin sensitizers (Class 3.4), germ cell mutagenicity (3.5), carcinogenicity (3.6), reproductive toxicity (3.7), specific target organ toxicity for single and repeated exposures (3.8 and 3.9), and aspiration (3.10), as well as environmental hazards to the aquatic environment (4.1) and the ozone layer (4.2) proved more difficult. A key feature of the criteria for delineating thresholds for inhalation toxicity, flammability of gases and liquids, and skin corrosion is that the intensity of the hazard level posed by the materials in categories within each GHS class is represented and used to differentiate TRCs. No categorization exists within health hazards 3.4 to 3.10 or in environmental hazards 4.1 and 4.2 to differentiate the intensity or potency of those hazards. For example, the carcinogenicity of ethanol would be treated the same as that of 1-azoxypropane, which some studies have indicated has a potency eight orders of magnitude higher as measured by median toxic dose (TD50). The same holds true for environmental hazard classes 4.1 and 4.2. Inclusion of oral toxicity by ingestion in assigning the significance of a PSE also proved problematic. Ultimately, the committee determined that RP 754 should remain focused on acute process safety impacts such as flammability versus potential chronic impacts to health and the environment that require extended exposures. In the end, the committee rejected several proposed alternatives for basing TRCs on inclusion of all GHS classes as unsound indicators of the significance of a PSE.

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