Light-curtain safeguarding on a mechanical power press

December 23, 1998

Mr. Lloyd Pillsbury
Production Resources Incorporated
[Recipient address omitted]

Dear Mr. Pillsbury:

This is in response to your letter of October 6, regarding proper installation of presence sensing devices as safeguarding mechanisms according to the Occupational Safety and Health Administration's (OSHA's) standard, 29 CFR 1910.217.

Your inquiry related to the efficiency of light curtains as guarding devices to meet the intent of the standard under the conditions described for your particular work environment. As you indicated in your letter, in this situation, the effectiveness of the light curtain would not be maintained when employees may inadvertently walk in the press bed with the machine operational. Therefore, the device in question would not meet the intent of the standard under the circumstances that you have outlined in your letter.

In regard to your second question, whether muting is permissible after the upstroke cycle is completed, this practice would definitely be in violation of the standard requirement, §1910.217(c)(3)(iii)(d). That is, at the end of the upstroke cycle, there would be a potential for the press to complete the cycle and initiate downstroke.

Thank you for your inquiry. If you have questions regarding the preceding, please contact [the Directorate of Enforcement Programs at 202-693-1681].

Sincerely,

Richard E. Fairfax, Director
Directorate of Compliance Programs

October 6, 1998

U.S. Department of Labor
Office of General Industry-Compliance Assistance
OSHA-Room: N3107
200 Constitution Avenue
Washington, D.C. 20210

Gentlemen:

Our company is a distributor and installer of safety equipment for power presses. We currently have an application at a customer site where we need standards interpretation. A summary of the application and identification of the guarding problem follows:

Machine/System/Operation:

• 2000-ton air clutch mechanical power press with extremely large bed area
• Clutch brake control system is control reliable and includes brake monitoring
• The press has a long stopping time of .912 seconds
• Four operators run the machine, and each has a separate run station requiring concurrent operation of the palm buttons
• Single stroke operation requires operators to enter walkways in the press bed area to load and unload large piece parts

Point of operation guarding problems:

The employees and employer do not want the individual two hand control stations fixed at a safe distance due to physical restriction of the die loading and maintenance activities. Consequently, we are considering a presence-sensing device as the primary point of operation safeguarding device. Given the long stopping time it will be necessary to install vertical and horizontal light curtains to prevent walk though. This will also prevent any operator from moving his run station between the vertical light curtain and the bolster of the press.

Our guarding application concern involves the possibility of a maintenance person or passerby walking through the light curtains into the press bed unseen by the 4 operators. Some operators tend to look away from the die space while initiating the run buttons; therefore, it's possible for them to initiate a stroke with non-operational personnel in the press bed. This seems an unlikely possibility since someone would have to be extraordinarily negligent to walk in the press bed with the machine operational. Our first question to you is whether the 1910.217 standard requires the employer to deal with this problem.

if it is necessary to deal with the above problem, we'd propose the following solution. Install another light curtain system to scan across the top of the bottom die. This system would be muted during all parts of the stroke except for a 30 degree period around top dead center. This secondary guarding system acts as a trip prevention device in the event someone is in the die space. Muting for most of the stroke is required since the tooling will interrupt the light curtain during normal stroking of the press. Our standard's difficulty here is that 1910.217(c)(3)(iii)(d) allows muting on the upstroke and this application requires muting during over a much longer portion of the cycle. Can we mute the trip prevention device as described and still be compliant with the standard?

if you have questions please call me at my office or E-mail your questions to [email protected]. I look forward to your earliest convenient reply.

Regards,

Lloyd Pillsbury

[Corrected 11/30/2006]