“I just let emotion dictate what the arrangement is.”  Jeff Buckley, singer-songwriter

Emotion is a great way to approach the arrangement of music. As an approach to the arrangement of hazards in a facility that processes highly hazardous chemicals, however, it leaves a lot to be desired. So, OSHA’s Process Safety Management standard demands that process facilities take the arrangement of these hazards into account. They call it “facility siting”.

What Does OSHA Expect?

Specifically, 29 CFR 1910.119(e)(3)(v) requires “The process hazard analysis shall address facility siting.”

The standard gives no further information about what that entails.  The non-mandatory guidance on PHAs in Appendix C addresses methodologies and team composition, but is silent on the topic of facility siting.  What is clear from the standard is that a “PHA is directed toward analyzing potential causes and consequences of fires, explosions, releases of toxic or flammable chemicals and major spills of hazardous chemicals.”  Any efforts directed to facility siting should consider these events:  fires, explosions, and toxic releases.

Letters of Interpretation

When a regulation itself is not informative, letters of interpretation from OSHA are sometimes helpful in understanding OSHA expectations, although OSHA correctly points out that “OSHA requirements are set by statute, standards and regulations. Our interpretation letters explain these requirements and how they apply to particular circumstances, but they cannot create additional employer obligations.”  There are five letters of interpretation from OSHA that touch on facility siting.

  1. The most recent, dated February 1, 2010 and addressed to Senator David Vitter (R-La.), extends the definition of “equipment” to include blast resistant structures, and states that “during the facility siting evaluation, the employer must determine whether these equipment-containing structures are sufficient to protect employees and equipment from any identified hazards, such as explosions.” The letter goes on to state, “In short, employers must ensure that blast resistant structures that contain equipment used in a process are designed to be blast resistant in accordance with RAGAGEP.”  (Recognized and Generally Accepted Good Engineering Practice)
  2. The next most recent letter of interpretation, dated February 1, 2005, simply reminds us that facility siting must be considered as part of a PHA, within the larger context of considering a qualitative evaluation of consequences.
  3. The letter of interpretation dated June 22, 1998 addresses the requirements of a PHA revalidation and reminds us that revalidation must consider facility siting as well as the more typical subjects of revalidation, P&IDs and incident reports.
  4. The letter of interpretation dated June 1, 1995 is no longer relevant, in that it simply addressed the timing for initial PHAs following the promulgation of the PSM standard in 1992.
  5. The earliest letter of interpretation that touches on facility siting is dated October 28, 1992. It also discusses timing, and establishes the principal that each facility needs its own PHA, hence its own consideration of facility siting.

To summarize the letters of interpretation:  address facility siting.

Guidance for OSHA Inspectors

The audit guidance that OSHA prepares for its inspectors is another source of information about what OSHA expects. The most current guidance document is CPL 03-00-021, PSM Covered Chemical Facilities National Emphasis Program, dated January 17, 2017. Regarding facility siting, CPL 03-00-021 requires that “during the initial walkaround [inspectors] should observe potential hazards including, but not limited to, pipe work at risk of impact, corroded or leaking equipment, unit or control room siting and trailer location, and relief devices and vents that discharge to atmosphere.”

CPL 03-00-021 refers to an OSHA Archive Document, CPL 02-02-045, Process Safety Management of Highly Hazardous Chemicals– Compliance Guidelines and Enforcement Procedures, of which OSHA has issued several versions, the most recent dated September 1, 2015. In every version, the direction to inspectors regarding facility siting is unchanged. Inspectors are to review calculations, charts, and other documents to verify that the PHA considered facility siting. Specifically, OSHA lists

  • Safe distances for locating control rooms based on type of construction, quantities of hazardous materials, types of reactions and processes, pressures and temperatures
  • Presence of ignition sources
  • Fire protection facilities
  • Capabilities to respond to explosions
  • Drainage facilities
  • Location of fresh air intakes


Another source of information about what OSHA expects is in its citations.  During the Refining PSM National Emphasis Program in 2008, 294 citations were issued, of which 8 were related to facility siting.  The specific citations almost always started with a statement that the PHA did not address facility siting.  They then went on to list a variety of issues that should have been addressed as part of a facility siting study.  The issues fell into eight categories:

  • Fire protection design
  • HVAC intake location /HVAC failure
  • Proximity of occupied buildings to hazardous processes
  • Pipe rack location
  • Sewer systems
  • Traffic concerns
  • Vent discharge locations
  • Use of checklist

This last category referred to organizations that had checklists, but then did not use them.

The Need for RAGAGEP

This is OSHA’s position on recognized and generally accepted good engineering practices (RAGAGEPs):  a national consensus standard can be cited as a RAGAGEP, but no single standard can claim to be the RAGAGEP for any particular topic.  Unless explicitly incorporated by reference in a regulation, OSHA does not enforce any specific RAGAGEP.  However, OSHA does use national consensus standards as evidence that a hazard is a recognized hazard.

OSHA acknowledges several documents as national consensus standards. These include API RP 752, API RP 753, and guidelines published by the AIChE’s Center for Chemical Process Safety. Since these are RAGAGEPs, it is important to review them for the advice they give on recognized hazards.

Top 12 Issues

Taken together, it becomes clear that OSHA expects that a facility siting study will address the following dozen issues:

  • Proximity of occupied buildings to hazardous processes – Are occupied buildings too close to hazardous processes?
  • Unit siting issues – Are there general issues associated with where the unit is, in relation to the rest of the facility? Is spacing adequate, in terms of other parts of the facility being a source of ignition or initiating failure?  Is spacing adequate in the event of a fire or explosion in the unit, in regard to its impact on other parts of the facility?
  • Control room siting issues – Are there issues associated with where the control room is in relation to the unit it controls and in relation to other hazardous processes? Can it withstand a hazardous event in the unit it controls or other hazardous processes?
  • Trailer location concerns– Are there general issues associated with where construction trailers and other “temporary” buildings are, in relation to the rest of the facility, especially in relation to the unit it controls and in relation to other hazardous processes?
  • Fire protection design – Do emergency vehicles have access to the hazardous process? Can the hazardous process be accessed from at least one side with firefighting measures?
  • Sewer systems – Would a fire or other abnormal situation ignite flammable material in the sewer system, so that the sewer became a source for spreading the fire?
  • Pipe rack location – Do pipelines carrying hazardous chemicals pass close by occupied buildings, where a leak would result in employee exposure?
  • Traffic concerns – Does fork truck or automotive traffic in or around the hazardous process expose pipe work or other equipment to impact and subsequent damage and release? Would an event in a hazardous process impact nearby traffic?
  • HVAC intake locations – Will the HVAC pull toxic or flammable vapors into an occupied space, exposing the employees there?
  • HVAC failure – Will the loss of a HVAC air handling unit result in the loss of positive pressure in an occupied space that depends on that positive pressure to keep toxic or flammable vapors out?
  • Relief device discharge locations – Do emergency vents discharge to locations that would place employees at risk of exposure suddenly and unexpectedly?
  • Atmospheric vent discharge locations – Do normal process vents put employees at risk, especially in an emergency when the composition of the vented material is abnormally toxic or flammable? Does the vent discharge to points near HVAC intakes?

Do It, Use It, Review It

When it comes to facility siting studies, OSHA’s primary expectation is that your PHA address facility siting. If you haven’t explicitly conducted a facility siting study, do it. If your organization has a facility siting checklist, use it.

If you have a facility siting study, you are already ahead of most of the employers that OSHA cited for facility siting issues. Just the same, review it. There are issues OSHA expects to see addressed and you should make sure they are. Show calculations; OSHA is impatient with mere assertion.

Finally, follow through. Facility siting is part of the PHA, and OSHA requires employers to promptly address findings and recommendations from a PHA.