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 http://www.osha.gov.

February 6, 1996

Mr. Guy Van Cleve, Jr., P. E.,
Manager, Process Engineering
Petrocon Engineering, Inc.
P. 0. Box 20397
Beumont, TX 77720-0397

Dear Mr. Van Cleve:

This is in response to your letter of June 5, 1995, addressed to Mr. Ray Skinner, regarding applicable regulations (i.e., §1910.106) and design calculation factors which can be used for tanks and vessels. Your letter was forwarded to our office for response. Please accept our apologies for the delay in responding to you.

Following are your specific questions and our responses.

  • Ql:

    The first question concerns the correct guideline to use for sizing fire case relieving scenarios. We have been told that since 1910.106 is referenced as the standard to be used for sizing tanks and it requires the use of NFPA 30, it takes precedence over the API RP 520 method. While this is clear with respect to tanks, is it meant also to apply to vessels? Some of the attendees of the FORUM (including the writer, believe they heard that it was to apply to vessels as well as tanks).

    R:

    With regard to the hierarchy of standards, The Flammable and Combustible Liquids standard, §1910.106 takes precedence over NFPA 30. Please note however, that an installation in accordance with NFPA 30 is acceptable to OSHA, so long as the guideline for sizing atmospheric tanks and pressure vessels in the NFPA 30 is at least as safe and protective as that of §l910.106. Although the API RP 520 could be used as a guideline, OSHA requires compliance with §l910.106 and may in specific circumstances accept NFPA 30, in accordance with the de minimus policy. Your first question was also concerned with whether the correct guideline for sizing is to apply to vessels as well as tanks. Please note that §l910.106 applies to atmospheric tanks as well as vessels (low pressure vessels and pressure vessels). In regard to pressure vessels, the standard references the ASME Boiler and Vessel Code of 1968 for their construction. Therefore, you are correct that §l910.106 applies to atmospheric tanks as well as pressure vessels.

    Q2:

    The second question has to do with design calculations factors which can be used for insulation. API RP 520 and 521 and NFPA 30 all specify that covering must remain intact at 1660 degrees F.

     

    Aluminum sheet obviously will not withstand the specified temperature, so credit could not be taken for either aluminum sheet or aluminum banding. However, some engineers argue that application of insulation using either steel or stainless steel banding or wire, properly spaced, satisfies the guidelines even when covered by aluminum sheet. They argue that, with proper band spacing, the insulation will resist dislodgement with or without the sheet covering.

    R:

    We regret that at this time, we do not have enough information to be able to determine whether the application of insulation using either steel or stainless steel banding or wire, properly spaced, satisfies the guidelines (even when covered by aluminum sheet). Although the use of aluminum sheathing and bands to secure insulation in place is compromised when sheathing and banding fails due to melting in fires, we could not locate any information regarding design factors associated with the stainless steel banding and spacing. Please note that it is not possible to render our opinion on this issue without detailed information, including design safety factors, previous installations and associated data (recommendations and certifications by professional engineers or associations, testing laboratories, insurance carriers, etc.) and risk assessments of potential failures.

     

    In summary, in order to formulate a practical and effective response to this question, OSHA would need to be provided with the information that consists of the basis for reaching the conclusion that with proper stainless steel band spacing, etc., the insulation would stay intact under all circumstances, and satisfy the guidelines of §l910.106, or NFPA 30, even when covered by aluminum sheet.

Thank you for bringing your concerns to our attention. If you need further assistance, please contact Alcmene Haloftis of my staff at 202-219-8031.

Sincerely,

John B. Miles, Jr., Director
Directorate of Compliance Programs