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.

November 18, 1976

MEMORANDUM FOR: Robert C. Tice-Regional Administrator ATTN: C. R. Holder-ARA for Technical Support
Subject: Clarification of Difference Between 29 CFR 1910.106(d)(4)(iii) and 29 CFR 1926.152(b)(4)(v)

This is in response to your request of June 15, 1976, concerning a clarification of the two subject standards for Dr. C. Ray Asfahl of the University of Arkansas.

Class 1, Division 1, locations are where hazardous concentrations of flammable gases or vapors exist continuously, intermittently, or periodically under normal conditions.

Class 1, Division 2, locations are where volatile flammable liquids or flammable gases are handled, processed or used, but in which the hazardous liquids, vapors or gases will normally be confined within closed containers or closed systems from which they can escape only in case of accidental rupture or breakdown of such containers or systems, or in case of abnormal operation of equipment and in which hazardous concentrations of gases or vapors are normally prevented by positive mechanical ventilation, but which might become hazardous through failure or abnormal operation of the ventilating equipment.

The work environment found in the construction industry, being of a temporary and dynamic state, warrants the inside storage rooms for flammable and combustible liquids be classified as Class 1 Division 1 locations for electrical wiring and equipment. Storage areas are used for handling, transferring of liquids, spills, open and ruptured containers. These are normal conditions for the storage areas in construction because the areas are subject to traffic from employees of other employers, and are more difficult to control than the storage areas in general industry which usually are permanent facilities with positive mechanical ventilation systems.

The two standards have been written to be applied to their respective industries. The intent of both standards is to prevent a fire or an explosion from flammable gases or vapor which may accumulate in an inside storage room for flammable and combustible liquids.

Richard P. Wilson
Acting Director,
Federal Compliance and State Programs