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.

July 26, 1977

Mr. Leon Najman
Vice President of Marketing
Gordon Engineering Corporation
Del Mar Drive
Brookfield, Connecticut 06804

Dear Mr. Najman:

This is in response to your letter dated June 21, 1977, concerning presence sensing devices used to actuate mechanical power presses. Your main concern is that the Occupational Safety and Health Administration (OSHA) should not consider revising the existing standard to allow the use of presence sensing devices as a tripping mechanism on mechanical power presses.

The variance granted August 31, 1976, to Interlake Stamping Corporation was an experimental variance for a period of one year. The variance authorized this company to conduct an experiment at its Willoughby, Ohio, facility, using an Erwin Sick electronic light curtain to function as a combined presence sensing device and a tripping mechanism on five Bliss-OBI mechanical power presses. This procedure is in lieu of complying with 29 CFR 1910.217(c)(3)(iii)(b), which prohibits the presence sensing device from being used as a tripping means to initiate the slide motion.

The experimental system which will be used has been used for many years in Sweden and West Germany. European standards have been developed governing its use. The equipment will be operated in accordance with the Swedish safety standards governing the use of a light curtain as a means of tripping the press. Therefore, it is not necessary to develop totally new information, but simply to validate the European information in American use.

The Erwin Sick electronic light curtain is part of a sophisticated electronic system which automatically checks all systems between strokes. If any of the electronic or mechanical systems do not operate properly, the press will shut down without stroking. In addition, the press will automatically shut down if the brake does not stop the press within a predetermined period, or if the operating rhythm is interrupted so that the press does not cycle within a preset time. Before the press can be operated again, necessary repairs or adjustments must be made and special operating means actuated to restart the press. Rigid guarding surrounds the light curtain on all sides, preventing entry to the die area from any direction except that portion protected by the light curtain.

It was determined that granting the variance for the experiment is a valid means for OSHA to evaluate the system and validate a new improved technique to safeguard the safety of workers operating mechanical power presses.

Your comments on the issue are sincerely appreciated and will be given full consideration should OSHA decide to take any further action concerning the use of presence sensing devices as a tripping mechanism on mechanical power presses.

Thank you for your concern and continuing interest in occupational safety and health. If I may be of any further assistance, please feel free to contact me.


Basil J. Whiting, Jr.
Deputy Assistant Secretary