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Standard Interpretations - (Archived) Table of Contents
• Standard Number: 1910.147; 1910.147(c)(1); 1910.147(a)(2)(ii)
• Status: Archived

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NOTICE: This is an OSHA Archive Document, and may no longer represent OSHA Policy. It is presented here as historical content, for research and review purposes only.

July 15, 2003

Mr. David Teague
Project Engineer
James Hardie Building Products
10901 Elm Avenue
Fontana, CA 992337

Dear Mr. Teague:

Thank you for your April 30, 2002 letter to the Occupational Safety and Health Administration's (OSHA's) Directorate of Enforcement Programs (DEP). This letter constitutes OSHA's interpretation only of the requirements discussed and may not be applicable to any scenario not delineated within your original correspondence. You had specific questions regarding the Control of hazardous energy (lockout/tagout), 29 CFR1910.147, standard. We apologize for the delay in our response.

Scenario: You have provided a Proposed E-Stop/Lockout Implementation circuit diagram and information about all of the system components for our review. Your system design intent is to allow for a safe way for your maintenance and operating personnel to lock out this machine. The dual channel E-stop string is monitored and powered by a safety relay and it has continuous monitoring for opens or shorts. The output will use redundant safety contactors to break the power supply of the load. The circuit is designed such that a single failure of any part of the system will still provide for the stop function and will prevent any attempt at restarting (as per European standard EN 954-1, Category 4).

Question: Is it permissible to use a lockable switch in an e-stop string as an acceptable lockout device?

Reply: No. Section 1910.147(c)(1) requires that before any employee performs servicing or maintenance on a machine or equipment where the unexpected energizing, start-up, or release of stored energy could occur and cause injury, the machine or equipment shall be isolated from the energy source, and rendered inoperative. Machines and equipment are isolated from energy sources by energy isolating devices.

It appears from the literature enclosed with your letter that the devices in question are control-circuit-type devices. The standard prohibits the use of motor-control-circuit switches and relays as energy isolating devices. Thus, pursuant to the standard, such mechanisms cannot be used to control hazardous energy.

However, a circuit that meets the control reliability and control-component-failure-protection requirements of the American National Standards for machine tools (ANSI B11.19-1990) would provide alternative safeguarding measures with respect to the minor servicing exception contained in 1910.147(a)(2)(ii). In other words, a circuit meeting the above referenced control reliability standards may be used in cases in which minor tool changes and adjustment, and other minor servicing activities, are performed during normal production operations, and are routine, repetitive, and integral to the use of equipment for production.

It is important to apply this safeguard through a hazard analysis process on a case-by-case basis in order to assure that it, in fact, provides effective employee protection. In regard to your enclosed design information, our office has not performed a detailed review, nor approved the adequacy of such design in meeting the above referenced OSHA, ANSI, or any other consensus standards. OSHA does not test, approve, certify, or endorse any equipment or product, including machinery.

In the event you wish to request a variance from a standard for servicing and maintenance activities that do not fall within the minor servicing exception, you may contact the Office of Technical Programs and Coordination Activities at 200 Constitution Avenue, NW, Washington, D.C. 20210, in Room N-3655; Telephone Number, 202-693-2110.

Thank you for your interest in occupational safety and health. We hope you find this information helpful. 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
http://www.osha.gov. If you have any further questions, please feel free to contact the Office of General Industry Enforcement at (202) 693-1850.


Richard E. Fairfax, Director
Directorate of Enforcement Programs

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.

Standard Interpretations - (Archived) Table of Contents

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