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.

March 26, 1996

Dick Hibdon, Engineering Consultant
American Bakers Cooperative Inc.
P.O. Box 308
122 Randolph Ave. Suite 202
Clifton, NJ 07011

Dear Mr. Hibdon:

This is a response to your letter of April 25, 1995 requesting an interpretation from the Occupational Safety and Health Administration's, Bakery Equipment Standard, 29 CFR 1910.263. Specifically, you asked when an oven must be preventilated, and when it is permissible to simply reopen the safety shut-off valves after they have been closed by a safety device. We regret that due to increasing requests for letters of interpretation or clarification, we were unable to respond to your inquiry in a shorter time frame.

OSHA promulgation of 1910.263 was based on the American National Standards Institute's (ANSI) Z50.1-1947, Safety Code for Bakery Equipment as a National Consensus Standard. The National Fire Protection Association's (NFPA) Standard for Ovens and Furnaces serves as the basis for the coverage of ovens and furnaces within the ANSI Z50.1 standard currently in use. OSHA generally accepts the latest revision (1995) of the NFPA standards as being able to provide equal or greater protection than the OSHA standards.

NFPA 86, Ovens and Furnaces, paragraph 560-9 states:

Purging Cycle or Preventilation.

(a) Timed preventilation is required for all ovens and heaters in which flammable vapors or fuel can accumulate during a shut down.

(b) Timed preventilation may be omitted on ovens of less than 350 cu. ft. volume, if doors must be opened to light burners or turn on heat, provided that the area of doors gives an explosion venting area of 1 sq. ft. to 15 cu. ft. of oven volume and all fans are operating. Doors shall be equipped with approved explosion relieving hardware.

(d) Where preventilation is required an approved time delay relay (see 510-1) shall be arranged in the safety control circuit and set so as to require operation of exhaust and recirculating fans for sufficient time to provide a minimum of four complete oven volume air changes with fresh air before the burner ignition system may be operated, fuel turned on, or the conveyor operated. Where conditions are such that safe preventilation may be secured with less than four air changes, the approval of the authority having jurisdiction should be secured.

If you have any questions or concerns, please feel free to contact Russelle R. McCollough of my staff, at (202)219-8031.


Raymond E. Donnelly, Director
Office of General Industry Compliance