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Standard Interpretations - Table of Contents
• Standard Number: 1910.119; 1910.119(d)(3); 1910.119(e); 1910.119(j); 1910.119(l)

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. This letter constitutes OSHA's interpretation of the requirements discussed. Note that our enforcement guidance may be affected by changes to OSHA rules. Also, from time to time we update our guidance in response to new information. To keep apprised of such developments, you can consult OSHA's website at

February 1, 2010

The Honorable David Vitter
United States Senate
Washington, DC 20510

Dear Senator Vitter:

Thank you for your January 24, 2008 and November 21, 2008 letters to the Occupational Safety and Health Administration (OSHA) regarding OSHA's Process Safety Management of Highly Hazardous Chemicals (PSM) standard at 29 CFR 1910.119. In your letters, you ask if the PSM standard's mechanical integrity (MI) requirements apply to structures located by refinery employers in areas exposed to explosion hazards. I apologize for the delay in our response.

First, I must stress that it is imperative that workers in structures exposed to explosion hazards are properly protected. When an employer determines, or should have determined, that a structure must be blast resistant (a "blast resistant structure"), that structure must be designed and maintained to meet robust blast resistance standards in accordance with recognized and generally accepted good engineering practices (RAGAGEP). This is required by both OSHA's process safety management standard and by the Occupational Safety and Health Act's (OSH Act's) general duty clause.

As we explain below, the MI provision itself applies to many, but not all, blast resistant structures. This provision is one part of a comprehensive system of requirements that work together to ensure employee protection against explosion hazards resulting from process operations.

Blast resistant structures that contain process equipment: The PSM standard includes comprehensive protections applicable to blast resistant structures that contain process equipment to ensure that the structures are fabricated (when applicable), installed, and maintained as required by the PSM standard.

The standard requires employers first to compile process safety information (PSI) including information related to the equipment in the process. Employers must document the codes and standards used to design the equipment (1910.119(d)(3)(i)(F)). Additionally, employers must document that all equipment complies with RAGAGEP (1910.119(d)(3)(ii)). This requirement includes documentation related to the ability of blast resistant structures that contain the equipment to withstand explosion hazards. RAGAGEPs relevant to structures used at facilities covered by the PSM standard include the American Society of Civil Engineers, Design of Blast Resistant Buildings in Petrochemical Facilities, and the Department of Defense, TMS-1300 Structures to Resist the Effects of Accidental Explosions, both of which provide guidelines for designing and constructing blast resistant buildings.

After compiling PSI, the employer must use the PSI, as well as other information, to conduct a process hazard analysis (PHA), which must include a facility siting evaluation (1910.119(e)(3)(v)). 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. If the employer finds deficiencies in any of these structures, the employer must address them and document how the deficiencies are resolved (1910.119(e)(5)). This could involve steps such as strengthening, replacing, or relocating the affected structures.

Similarly, if an employer installs or modifies a structure between required PHAs, then the employer must develop and implement a management-of-change (MOC) procedure prior to the installation or modification (1910.119(l)). Like the PHA, the MOC procedure must address the safety and health impacts (1910.119(l)(2)(ii)) of the installation or modification with respect to the structure, occupants, and equipment housed in the structure. Following these evaluations, the employer is then required (1910.119(l)(4)) to update the PSI, including documenting that the new or modified structure complies with RAGAGEP. The employer's PHA team must address the change (i.e., installation or modification of the structure) in its next PHA revalidation (1910.119(e)(6)).

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. The employer must also evaluate any changes to be made to the structures, and update the design information as appropriate to ensure that the structures continue to be consistent with RAGAGEP.

In addition, the standard's mechanical integrity (MI) provision, where it applies, requires that new equipment, in this case blast resistant structures, must be fabricated so as to be suitable for the process application for which it will be used (1910.l19(j)(6)(i)). The MI provision applies to listed categories of process equipment, e.g., controls and emergency shutdown systems (1910.119(j)(1)). Structures near hazardous process operations frequently contain such equipment. OSHA has also said that if the employer deems any other equipment to be critical to process safety, the employer should consider that equipment to be covered by the MI provision and treat it accordingly (57 Fed. Reg. 6389 (Feb. 24, 1992)). Blast resistant structures that contain equipment that is covered by the MI provision are subject to the MI requirements. Pursuant to those requirements, employers must also perform appropriate checks and inspections for both new and existing structures to assure that the structures are installed properly and consistent with design specifications and the manufacturer's instructions (1910.119(j)(6)(ii)). The MI provision also requires the employer to establish written procedures to maintain the ongoing integrity of process equipment (1910.119(j)(2)), including inspection and testing procedures that meet RAGAGEP (1910.119(j)(4)(ii)), and it must correct deficiencies (1910.119(j)(5)).

Even when blast resistant structures contain process equipment not covered by the MI provision, the structures are still subject to the other PSM provisions noted above, and by the general duty clause. The general duty clause requires all employers to provide a place of employment that is free of serious recognized hazards. Under the general duty clause, the employer must take the steps that knowledgeable safety experts consider necessary to protect against serious hazards. This would include ensuring that blast resistant structures comply with RAGAGEP.

Blast Resistant Structures that do not contain process equipment: Other blast resistant structures may not contain any equipment used in a process, for example, offices, maintenance shops, and trailers or "pods" whose function is solely to provide weather protection for workers. Blast resistant structures that are not part of the process are still protected by the PHA and MOC provisions of the PSM standard and by the general duty clause. The employer PHA must address requirements such as evaluations of facility siting, the consequences of a failure of process controls, and a "qualitative evaluation of a range of the possible safety and health effects of failure of controls on employees in the workplace" (1910.119(e)(3)(v)-(vii)). The standard also requires the employer to address the PHA findings "promptly" (1910.119(e)(5)). This means that if a PHA discloses that a blast resistant structure is not adequate to protect workers from an explosion hazard, the employer must remedy that situation, either by reinforcing the structure in accord with RAGAGEP, relocating the workers, or controlling the source of the hazard. Moreover, the general duty clause would also prohibit an employer from placing employees in a blast resistant structure without maintaining the structure's blast resistance in accordance with RAGAGEP.

I hope that the above responds to your inquiry. Should you have any additional questions, please feel free to contact Janna Bergquist in the Office of Congressional and Intergovernmental Affairs any time at (202) 693-4649.


David Michaels, PhD, MPH

Standard Interpretations - Table of Contents

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