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.

January 26, 1976

Mr. John R. Reilly
Corporate Safety Director
Corporate Headquarters
Fisher Scientific Company
711 Forbes Avenue
Pittsburgh, PA 15219

Dear Mr. Reilly:

Your letter of January 16, 1976 requested definition of the phrase "Adequate ventilation" as used in 29 CFR 1910.178(g)(2). The source of this standard is National Fire Protection Association No. 505 - 1969: Powered Industrial Trucks, Section 700--Changing and Charging Storage Batteries.

"Adequate ventilation" as used in the indicated standard means providing natural, mechanical--general, or mechanical dilution ventilation sufficient to limit the accumulation of hydrogen gas in air at the charging site to levels below the lower explosive limit (4.1%).

A "typical exhaust fan" could meet this requirement if it were used in a manner such that the concentrations of the hydrogen gas in the fan's ambient air never exceeded the lower explosive limit.

Thank you for your interest in a safe workplace.

Sincerely yours,

Regional Administrator