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 https://www.osha.gov.


December 16, 1985




Regional Administrator
Directorate of Field Operations
SUBJECT: Applicability of Section 1910.106 to Chemical Plants

Reference is made to your memorandum dated November 11, 1985, subject as above.

Attached are the answers to the questions posed in the memorandum.

Applicability of 29 CFR 1910.106 to Chemical Plants

(Answers In Response to Region 111 Memorandum dated November 11, 1985)

Questions 1a: Is 1910.106(c) applicable to chemical plants or is there a consensus standard which can be used to evaluate piping?

Response: 1910.106(c) is applicable to chemical plants since they are not specifically exempted under 1910.106(c)(1)(ii).

Question 1b: Would Section (5)(a)(1) citation policy preclude the issuance of a general duty citation for the state of the art piping requirements, ANSI B31.3?

Response: An OSHAct Sec. 5(a)(1) citation is improper because 1910.106(c)(1)(i) specifically permits the application of ANSI B31 series requirement relative to hazards. Therefore, since 1910.106(c) is essentially a performance standard, 1910.106(c) should be cited with reference to applicable ANSI B31 series specifications.

Question 1c: If the ANSI B31.3 standard is used, what year of issue of the standard should be referenced?

Response: The ANSI B31 series standard in effect on the date of incorporation by 1910.106 is the appropriate standard.

They are as follows:

ANSI B31.1-1967 ANSI B31.2-1968 ANSI B31.3-1966 ANSI B31.4-1966 USASI B31.5-1966

Question 2a: Since 1910.106(i) does not address "incidental usage and container and portable tank storage," can 1910.106(d) and 1910.106(e) be used to evaluate compliance in captive operations of a chemical plant, such as maintenance shops and warehouses?

Response: The 1910.106(i) does, in a general way, deal with incidental usage, container and portable tank storage. 1910.106(d) and (e) cannot be used as they exclude chemical plants since 1910.106(a)(8) defines a chemical plant as, "a large integrated plant or that portion of such plant...where flammable or combustible liquids are produced by chemical reactions or used in chemical reactions."

Question 2b: Would warehouse operations be exempted from 1910.106(d) even though the fire hazards are the same in the chemical plant warehouse as an industrial plant warehouse (especially since the intent of NFPA was to require the same fire protection requirements for warehouses containing flammable and combustible liquids)?

Response: Warehousing operations in a chemical plant are exempt from 1910.106(d).

Question 2c: Should maintenance shop use of flammable and combustible liquids be regulated by 1910.106(e) since its scope includes incidental use of liquids and unit physical operations?

Response: Maintenance shops with chemical plants are exempt from 1910.106(e).

Question 3: Although the handling of flammable and combustible liquids at wharves of chemical plants is specifically covered by subsection 1910.106(i), by reference to 1910.106(f)(4), is the use of the standard precluded by coverage under OSHA's "Maritime Safety and Health Standards"?

Response: The use of 1910.106(f)(4) is not precluded by the Maritime standards. None of the Maritime standards are applicable to bulk transfer of liquid cargo to and from ships or vessels. 1910.106(f)(4) is applicable to the handling of flammable and combustible liquid cargo to and from ships and vessels, and effects the equipment and procedures from the shore facility up to the ship hook-up flange (vessel flange connection). All onboard ship/vessel liquid cargo transfer and handling systems are under the jurisdiction of the U.S. Coast Guard and must comply with their requirements.

Question 4: Are compressed gases, such as ethylene oxide, because of their liquid state during storage and use, covered by the provisions of 1910.106?

Response: No. Liquified compressed gas, such as ethylene oxide (EtO), is outside the scope of 1910.106. EtO is regulated as toxic substance under 1910.1047. Hazardous circumstances associated with liquified compressed gases, other than LPG which are regulated at 1910.110, are OSHAct Sec. (5)(a)(1) violations. Documents such as CGA S-1.3-1980 by the Compresses Gas Association may be used to support OSHAct Sec. 5(a)(1) violations. 1910.1047 Appendix B, II, may be used to verify the presence of hazardous circumstances relating to fire or explosion regarding EtO.

Question 5: Should 1910.106 be interpreted to require pressure vessels built prior to 1968 to comply with this code?

Response: Yes. 1910.106(b)(1)(v)(b) requires, as a minimum, that unfired pressure vessels comply with the ASME Boiler and Pressure Vessel Code-1968. 1910.106(i)(3) requires, as a minimum, that in chemical plants fired and unfired pressure vessels comply with the ASME Boiler and Pressure Vessel Code-1968. There is no grandfathering.

Question 6a: Are the requirements for determining emergency relief venting capacity in 1910.106(b)(2)(v) applicable to processing vessels of unit operations, such as reactors, mixers, and heat exchangers, which are used to contain flammable and combustible liquids?

Response: No. 1910.106(b)(2)(v) applies only to aboveground storage tanks and vessels. However, the Compressed Gas Associations's CGA S-1.3-1980, Pressure Relief Device Standards, may be used to support OSHAct Sec. 5(a)(1) findings.

Question 6b: Are the API 520 and API 521 standards the most recognized practices to calculate emergency relieving systems for unfired pressure vessels?

Response: 1910.106(i)(3)(ii), which references the requirements of the ASME 1968 Code, is the sole standard applicable. Of course, the use of equal or better procedures are recognized as de minimis.

Question 6c: As mentioned in the API 2000 and 1910.106(b)(2)(v)(c), standards for aboveground storage tanks, should different considerations for the calculations of pressure vessel emergency relieving devices be taken for unstable liquids?

Response: Yes. The ASME Codes UG-125 through UG-136 or CGA S-1.3-1980, Sections 4 and 5, may be used for calculation purposes.

Question 7a: How is a "flood area" defined for the purpose of 1910.106(b)(5)(iv)?

Response: Any location where a tank is located in an area subjected to flooding either from a natural event or from an internal process, procedure, or malfunction.

Question 7b: What document would provide adequate documentation to demonstrate this "flood area"?

Response: Internal corporate records, local building and safety department records, or insurance company data, may be used in conjunction with the Army Corps of Engineers 100-year record. The Army complies the data from the Federal Emergency Management Agency (FEMA) as Flood Plain Information Studies. These studies are overseen by: Mr. Jerry Peterson, DAEN-CWP-F, in the Office of the Chief of Engineers in Washington, D.C. Telephone Number 202-272-0169 Specific data, is available, may be requested from him.

Question 8: Should the specific standard in 1910.106(i) be cited when referencing another standard or should the referenced standard be cited?; i.e., should 1910.106(i)(1) be cited for alleged violations of the tank storage requirements, or should the specific section in 1910.106(b) be cited?

Response: The specific standard violated should be cited with a reference to the standard under which such authority or coverage is specified.

[Corrected 4/24/2009]