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Standard Interpretations - Table of Contents
• Standard Number: 1910.147; 1910.147(a)(2)(ii); 1910.147(a)(2)(iii)(A); 1910.147(b); 1910.212

This letter constitutes OSHA's interpretation only of the requirements discussed and may not be applicable to any situation not delineated within the original correspondence.

December 28, 2006

Mr. Milt Kershaw
Safety & Health Consultant
Allied Resources Corporation
106 Pitkin Street
East Hartford, CT 06108

Dear Mr. Kershaw:

Thank you for your August 17, 2006 letter to the Occupational Safety and Health Administration (OSHA). You requested an interpretation regarding machine set-up and OSHA's Control of hazardous energy (lockout/tagout), 29 CFR §1910.147, standard. You also referenced an OSHA interpretation letter, dated April 22, 2005, that addresses hydraulic power press lockout/tagout (LOTO) requirements for die-setting operations. Your paraphrased scenario, questions, and replies follow:

Scenario: Our current customer operates its hydraulic power presses during normal production via redundant safeguards that include properly designed two-hand controls and presence-sensing devices. Both safeguarding devices are located a safe distance from the point-of-operation. The presses are run in single stroke with hands in the die area.

An additional safeguard includes automatic swing blocks that are cycled in and out of the die area on each single stroke. During die-setting, if the main disconnect is in the on position, the press cannot be operated unless the two-hand controls are actuated and the presence-sensing device is unobstructed. The customer cannot recall a catastrophic failure of the hydraulic system and in the extremely unlikely situation of a catastrophic hydraulic failure, locking the main disconnect would not prevent the upper slide from descending.

Additionally, when dies are changed, the upper slide is in its lowest position so as to safely remove the die. When a die-setter is working on the dies while the dies are installed in the press, the automatic swing blocks are in place between the upper slide and the press's bolster plate.

Question: Under the conditions described above, does OSHA's Lockout/Tagout Standard, 29 CFR 1910.147, apply?

Reply: Yes. Die-setting activities constitute servicing activities and are covered by the LOTO standard — i.e., pursuant to the definitions for Setting up and Servicing and/or maintenance contained in §1910.147(b). Also, the General requirement for all machines requirements, contained in §1910.212, apply with respect to the hydraulic power press operation during normal production operations.

The safety blocks (or as you call them swing blocks) described in your scenario appear to be used to protect employees from hazardous energy (e.g., unexpected drift or movement of the slide due to gravity) during the die-setting procedure. Safety blocks, as well as electric disconnect switches are energy isolating devices if they physically prevent the transmission or release of energy. See the §1910.147(b) definition of Energy isolating device.

Although the safety blocks you describe may provide some protection, the reliance on control circuit devices (i.e., two-hand controls and/or a light curtain) alone or together may not protect employees from other types of hazards because neither safeguarding device physically prevents the transmission or release of hazardous energy. For example, the use of control circuitry alone does not prevent employee exposure to hazardous energy that may result from unexpected ram movement caused by potential mechanical energy (resultant from the ram/slide position and associated gravitational force), press component or control system malfunction, or press activation by others.

Question: If the answer to the first question is Yes, does it follow that it will be necessary to apply the rules in the OSHA Lockout/Tagout Standard when changing a grinding wheel on a surface grinder or changing a drill bit on a radial arm drill press or for that matter during the setup of any machine tool?

Reply: Yes, unless the set-up activity meets one of the following LOTO standard exceptions:

  1. The minor servicing exception, contained in the §1910.147(a)(2)(ii) note, provides that: Minor tool changes and adjustments, and other minor servicing activities, which take place during normal production operations, are not covered by this standard if they are routine, repetitive, and integral to the use of the equipment for production, provided that the work is performed using alternative measures which provide effective protection (see Subpart O of this Part).

  2. The cord- and plug-connected equipment exception, contained in §1910.147(a)(2)(iii)(A), states that the LOTO standard does not apply to: Work on cord and plug connected electric equipment for which exposure to the hazards of unexpected energization or start up of the equipment is controlled by the unplugging the equipment from the energy source and by the plug being under the exclusive control of the employee performing the servicing or maintenance.

With respect to changing a grinding wheel on a surface grinder, the wheel change takes place outside of the normal production process: i.e., the machine is turned off, grinding operations stop, a guard is removed, and the wheel retainer nut is loosened and removed. Therefore, the minor servicing exception does not apply and the energy source for the grinder would need to be locked or tagged out in accordance with this standard.1

In terms of the radial arm drill press question, minor tool changes and adjustments, which are routine and repetitive and must be performed as an integral part of the production process, are permitted to be performed without LOTO if the work is performed using alternative measures that provide effective protection. Electric disconnect switches or control switches are considered effective protection if the switches:

  1. Are properly designed and applied in accordance with recognized and good engineering practice; and

  2. Control all the hazardous energy and are placed in an off position; and

  3. Are under the exclusive control of the employee performing the task.

In the event the surface grinder or drill press wiring consists of a flexible cord equipped with an attachment plug connected to permanent wiring (as permitted by 29 CFR 1910, Subpart S), the employer may elect not to LOTO the equipment as long as: (1) the employer unplugs the cord- and plug-connected equipment; (2) unplugging controls all of the hazardous energy to which the employee may be exposed; and (3) the plug is in the exclusive control of the employee who is performing the tool change. See §1910.147(a)(2)(iii)(A) exception. In all other situations in which employees are performing servicing and maintenance activities and may be exposed to hazardous energy, LOTO must be performed to protect employees from hazardous energy.

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

1 The Occupational Safety and Health Review Commission (OSHRC) rejected an employer's assertion that set-up activities associated with a printer/slotter machine constituted servicing and/or maintenance within the scope of the minor servicing exception. The OSHRC concluded that adjustments made to prepare for the normal production operations cannot, at the same time, be adjustments that are made during normal production operations. As such, these setting up activities, by definition, cannot fall within the minor servicing exception. See Westvaco Corp. 16 (BNA) OSHRC 1374 (90-134, 1993). [ back to text ]

Standard Interpretations - Table of Contents

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