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 2, 1991

Wesley R. Van Pelt
Wesley R. Van Pelt Associates, Inc.
773 Paramus, New Jersey 07652

Dear Mr. Van Pelt:

Thank you for your letter of September 25 requesting interpretation of 29 CFR 1910.106(e)(3)(v)(a) and (b) on ventilation of industrial plants involved in flammable or combustible liquid operations within the scope of 29 CFR 1910.106(e)(1).

The answer is yes to your question: Do the requirements of both the aforementioned paragraphs (a) and (b) have to be met independently? The ventilation standard at 29 CFR 1910.106(e)(3)(v)(a) is with reference to industrial plant unit physical operations areas in general; whereas, the ventilation standard at 29 CFR 1910.106(e)(3)(v)(b) applies to equipment, used specifically in 29 CFR 1910.106(e)(3)(i) unit physical operations areas. The ventilation standard at 29 CFR 1910.106(e)(3)(v)(a) is an acceptable alternative to ventilation at a rate sufficient to maintain the concentration of vapors within enclosed processing areas at or below 25 percent of the lower flammable limit as required by ANSI/NFPA 30-1990, paragraph 5-3.3. This criterion is applicable to an enclosed processing area except at equipment used for unit physical operations where flammable vapor-air mixtures are limited to the equipment interior and to not more than 5 feet from the equipment which exposes Class I liquids to air. The design of the equipment enclosure and the capability of local ventilation dedicated to the equipment, in conjunction with the overall capability of the ventilation serving the enclosed process area are considerations on which compliance with 29 CFR 1910.106(e)(3)(v)(b) is predicated.

In addition to 29 CFR 1910.106(e), there are other general industry fire and explosion related ventilation standards at 1910.94, 1910.107 and [1910.123-1910.126] which may be applicable to flammable and combustible liquids applications in the workplace. Also, the standards at 29 CFR 1910.1000, which were developed for the prevention of harmful exposure to employees to workplace toxic and hazardous materials, may be applicable.

Thank you for your interest in occupational safety and health. If we may be of further assistance, please contact us.


Patricia K. Clark, Director
Directorate of Compliance Programs