Archive Notice - OSHA Archive

NOTICE: This is an OSHA Archive Document, and may no longer represent OSHA Policy. It is presented here as historical content, for research and review purposes only.

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

October 20, 1998

Mr. Bob Eggleston
General Electric Company
P.O. Box 156301, Mail Drop T-165
One Neumann Way
Cincinnati, OH 45215-6301

Dear Mr. Eggleston:

This is in response to your March 19, 1998 letter requesting interpretation of the 29 CFR 1910.147 Control of hazardous energy (lockout/tagout) standard with respect to the operator change out of a grinding wheel on a tool room size surface grinder. Please accept our apology for the delay in responding. Your scenario, question and our response follows.


To change the grinding wheel, the operator shuts down the surface grinder with the controls on the front of the machine, removes the wheel guard (usually two hand knurled nuts) and proceeds to loosen the wheel retainer nut. The operator then removes the wheel and replaces it with another grade of wheel to finish the job. This change out task, which is limited to the front of the machine, is performed by a skilled toolmaker 3 to 5 times per day depending upon the job task at hand.

The operator is the only individual involved in the grinding wheel change out and the guards (some of which are side hinged) are approximately 6 x 8 inches in size. The operator has the stop button within his/her reach and immediate control during the change out operation. The start button is recessed and requires deliberate finger push activation to start up. If the operator were to energize the machine, he or she would be immediately aware of it.


Would interlocking the wheel guard with the grinding wheel motor such that the motor could not start up while the guard is removed preclude the need for locking/tagging out during grinding wheel change out?


No. The use of interlocked guards to prevent activation of the machine while the guard is not in place, in lieu of lockout or tagout, is permissible only for minor servicing activities which take place during normal production operations. In your scenario, the wheel change takes place outside of the normal production process: the machine is turned off, grinding operations stop, a guard is removed, and the wheel retainer nut is loosened and removed. Therefore, the 1910.147(a)(2)(ii) minor servicing exception does not apply and interlocked guards are no substitute for implementing the lockout or tagout devices according to this standard. We recognize that the energy source for the grinder is under the immediate control of the person performing the service. Although this would limit the risk of an unexpected activation of the grinder, it cannot remove it entirely.

In the event your grinder's power source is a flexible cord, then the lockout or tagout of the grinders is not required if the provisions of 1910.147(a)(2)(iii)(A) are met for cord and plug connected equipment. The exemption is predicated on the assumption that the use of the flexible cord is approved and suitable for the conditions of use and location as detailed in 1910.305(g).

We appreciate your interest in worker safety and health. If we can be of further assistance, please contact the Office of General Industry Compliance Assistance [at (202) 693-1850].


Richard Fairfax, Acting Director
Directorate of Compliance Programs