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PT Notes

Stationary Source Location and Emergency Shutdown

PT Notes is a series of topical technical notes on process safety provided periodically by Primatech for your benefit. Please feel free to provide feedback.

This PT Note describes EPA’s views relating to stationary source location and emergency shutdown in the context of proposed amendments to EPA's Risk Management Program (RMP) regulation.

Serious accidents often highlight numerous safety concerns and emphasize the need to consider existing regulations, industry standards, recommended practices and guidance to reduce risks of future incidents. Two issues of particular importance include the location of stationary sources and their emergency shutdown capabilities.

At this time, EPA is not proposing any additional requirements for the location of stationary sources or emergency shutdown systems. However, EPA is seeking comments on whether such requirements should be considered for future rulemakings.

These topics are described below.

Stationary Source Location

EPA believes that the location of stationary sources, and the location and configuration of regulated processes and equipment within a source, can significantly affect the severity of an accidental release. The location of the stationary source in relation to public and environmental receptors may exacerbate the impacts of an accidental release, such as blast overpressures or concentrations of toxic gases, or conversely may allow such effects to dissipate prior to reaching receptors.

The lack of sufficient distance between the source boundary and neighboring residential areas was a significant factor in the severity of several major chemical accidents, including, among others, the Bhopal disaster and the recent West Fertilizer accident. In the Bhopal disaster, most of the deaths and injuries occurred in a residential area that had grown up next to the plant. In the West Fertilizer accident, an apartment complex and a nursing home located approximately 450 feet and 600 feet, respectively, from the source of the explosion were heavily damaged, resulting in three public fatalities (a total of 15 people were killed in the explosion). The explosion also caused over 260 injuries, as well as damage to over 350 homes and three schools located near the plant.

Facility designers have long recognized the potential benefits of adding buffer or safety zones, that is, controlled areas separating the public and other facilities from the consequences of process incidents, when selecting the location for new chemical facilities. For existing facilities, owners have sometimes compensated nearby residents to relocate away from the facility boundary in order to create a buffer zone where one did not previously exist, or where adjacent residential areas had been developed after the facility itself was constructed.

The selection of locations of processes and process equipment within a stationary source can impact the surrounding community not only by the proximity of the accidental release to offsite receptors near the facility boundary, for example, people, infrastructure, and environmental resources, but also by increasing the likelihood of subsequent releases from other nearby processes compromised by the initial release.

The 1984 disaster at the PEMEX liquefied petroleum gas (LPG) tank farm in San Juan Ixhuatepec, Mexico, illustrates the potential for such effects. In this accident, an LPG pipeline rupture resulted in a large ground fire that spread to nearby LPG storage vessels, initiating a series of massive explosions. The cascading explosions and fires ultimately destroyed the entire facility and many nearby residences, resulting in over 500 fatalities and thousands of severe injuries.

In the United States in 2007, a large fire at the Valero McKee refinery in Sunray, Texas, resulted in the release of chlorine gas and sulfuric acid from an adjacent process, which prevented responders from entering the area and extinguishing the fire for more than two days.

At West Fertilizer, a RMP-regulated anhydrous ammonia process was located near the ammonium nitrate storage area. Although the ammonium nitrate explosion that occurred did not cause any catastrophic failure of the anhydrous ammonia storage vessels, the potential for a release existed. A 1994 explosion involving ammonium nitrate solution at Terra Industries in Port Neal, Iowa, which killed four workers, also damaged on-site ammonia tanks, creating an ammonia cloud that resulted in the evacuation of 2,500 people.

The PSM standard and RMP rule both require that facility siting be addressed as one element of a PHA. While EPA has not provided any guidance on how to adequately address stationary source siting in the PHA, RMP facility owners or operators can refer to industry guidance on siting considerations. The following publications provide guidance on facility siting:

  • API Recommended Practice 752, Management of Hazards Associated With Location of Process Plant Buildings, 3rd Edition, December 2009.
  • API Recommended Practice 753, Management of Hazards Associated with Location of Process Plant Portable Buildings, First Edition, June 2007.
  • CCPS Guidelines for Evaluating Process Plant Buildings for External Explosions, Fires, and Toxic Releases, Second Edition, 2012.
  • CCPS Guidelines for Facility Siting and Layout (2003).

The first three references focus on providing guidance and best practices on establishing the location of occupied buildings within a facility, but generally do not address the potential risks to offsite receptors associated with the location of the facility or processes within the facility, nor do they consider the potential for releases caused by natural hazards that may occur in particular locations. The CCPS Guidelines for Facility Siting and Layout address both external factors influencing site selection, as well as factors internal to the source that could influence site layout and equipment spacing.

At this time, EPA is not proposing any additional requirements for the location of stationary sources. However, EPA is seeking comments on whether such requirements should be considered for future rulemakings, including the scope of such requirements, or whether the Agency should publish guidance.

Emergency Shutdown

In addition to properly locating stationary sources in relation to surrounding receptors, and locating processes within sources so as to minimize the possibility of cascading release events, accidents such as those described above highlight the importance of being able to quickly and safely shut down processes where accidental releases are occurring or may imminently occur.

The RMP rule requires owners and operators of stationary sources to develop and implement written operating procedures for the safe and timely emergency shutdown of Program 2 and Program 3 processes, to ensure operator training for these procedures, and for maintaining the mechanical integrity of emergency shutdown systems. However, the regulation does not explicitly require that all covered processes must include emergency shutdown systems.

EPA encourages owner and operators of stationary sources to consider the location of stationary sources and process equipment and the adequacy of emergency shutdown systems at their facilities to determine if changes are necessary to both reduce risks of an accidental release and ensure that procedures are in-place to mitigate those effects. EPA believes that emergency shutdown or putting a process into a safe operation mode in the event of an emergency is a preventive safeguard to address hazard(s) identified as part of a hazard review or PHA. Thus, the required hazard review or PHA should identify the use of this safeguard, when appropriate.

At this time, EPA is not proposing any additional requirements for emergency shutdown systems. However, EPA is seeking comments on whether such requirements should be considered for future rulemakings, including the scope of such requirements, or whether the Agency should publish guidance.

Further details can be found at:


Comments on the proposed amendments must be submitted on or before May 13, 2016. Comments should be identified by docket EPA-HQ-OEM-2015-0725 and submitted through to the Federal eRulemaking Portal: http://www.regulations.gov.

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