Powered by GoogleTranslate
Standard Interpretations - Table of Contents
• Standard Number: 1910 Subpart O; 1910 Subpart S; 1910.147; 1910.147(a)(2)(ii); 1910.147(a)(2)(iii)(A); 1910.212; 1910.212(a)(3)(iv)

August 24, 2005

Mr. William H. Kincaid
Lockton Companies of St. Louis
Three City Place Drive
Suite 900
St. Louis, MO 63141

Dear Mr. Kincaid:

Thank you for your December 1, 2004 letter to the Occupational Safety and Health Administration's (OSHA's) Directorate of Enforcement Programs. This letter constitutes OSHA's interpretation only of the requirements discussed and may not be applicable to any questions not delineated within your original correspondence. You had specific questions regarding The control of hazardous energy (lockout/tagout) standard's, 29 CFR 1910.147, requirements for vertical/horizontal milling machine and drill press tool changes. Your paraphrased subject background (with comments), questions, and our replies follow:

Your Subject Background: You stated that OSHA has issued interpretation letters addressing the lockout/tagout (LOTO) "minor servicing" exception for certain tool changes, cleaning, un-jamming, and other minor servicing activities that are routine, repetitive, and integral to the use of machines for production purposes. You further stated that these activities are not covered by the LOTO standard if the work is performed using alternative protective measures that ensure employee safety, such as those required by 29 CFR 1910, Subpart O.

You have noted that the training requirements for, and skill levels of, milling machine operators are necessarily high in order to achieve the required milling precision and that there is no need for the operators to place their hands near the point of operation on milling machines during normal production operations. Parts are secured by clamps, oiling is accomplished continuously with coolant pumps, and the machine's controls are located well away from the points of operation.2  You indicated that these machines are seldom equipped with light curtains or other protective devices for the point-of-operation. You stated that there is a need to visually observe the point-of-operation while using these manually controlled machines, so it is unusual to see fixed guarding or interlocked hinged guards, such as one would expect to see on an automatic CNC milling machine. Therefore, there would not be any machine safety guards or protective devices over the tools being changed that would conform to 29 CFR 1910, Subpart O during the tool changing operation.3

You further explained that it is common practice for milling machine operators to change a tool after pushing the machine's stop button, without disconnecting the power supply to the machine.

All that is required to restart the machine is to push the start button. The start button is mounted on the front of the machine, in front of the operator who is doing the tool change. You indicated that, if another person were to approach the start button, they likely would be seen by the operator due to proximity of the operator to the switch.

Question #1: Would a lockout procedure be required for tool changes on manually controlled milling machines?

Reply: An energy control procedure would not be required if a tool change activity meets all of the criteria contained in the minor servicing exception, §1910.147(a)(2)(ii) Note, or if machine guarding methods eliminate employee exposure by preventing the employee from placing any part of his body in the machine's danger zone.
4  In both of these cases, the lockout/tagout (LOTO) standard would not apply. In addition, if the machine wiring consists of a flexible cord- connected by an attachment plug to the permanent wiring, as permitted by 29 CFR 1910, Subpart S, the LOTO standard, including the energy control procedure requirements, would not apply as long as: (1) the employer unplugs the cord- and plug-connected machinery, (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). 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.

Given your scenario, when the minor servicing exception criteria are met (as often can be the case with respect to activities like changing a tool bit on a milling machine or a drill bit on a drill press), servicing activities may be performed using local disconnects or control switches that:

  1. are placed in an "off" position;
  2. provide effective employee protection through proper design and application; and
  3. are under the exclusive control of the employee performing the task.5

Question #2: I note the similarity between the general configuration of a vertical milling machine and that of a drill press. Would a lockout procedure be required for changing a twist drill in a drill press?

Reply: The LOTO standard would not apply to minor servicing activities or to work on cord- and plug-connected machinery (as discussed above). See §§1910.147(a)(2)(ii) Note and 1910.147(a)(2)(iii)(A). Additionally, the LOTO standard does not apply if machine guarding eliminates the employee exposure to hazardous energy during servicing and maintenance activities.

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 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). [ back to text ]

2 Flexible, fixed coolant hoses occasionally vibrate out of position and must be re-positioned, which generally requires the milling machine operator to place his hands in close proximity to the cutting tool. In these situations, operators who shut off the milling machine and exercise exclusive control over the control circuit, as discussed in the Reply to Question #1, would not need to lockout/tagout (LOTO) the machine to re-position the hose. However, under no circumstance is a worker ever permitted to place any part of his body in a machine danger zone without following the requirements of the LOTO standard or the minor servicing exception, when applicable. See 1910.147(a)(2)(ii). [ back to text ]

3 The contention that vertical and horizontal milling machines are not usually provided with fixed guards and are seldom equipped with protective devices (e.g., light curtains) may reflect your experience, but this does not relieve an employer of its obligation to comply with the Machine guarding requirements contained in Subpart O of the general industry standards. Milling machines are specifically listed as machines that usually require point-of-operation guarding. See 1910.212 (a)(3)(iv). Furthermore, the Safety Requirements for Manual Milling, Drilling and Boring Machines with or without Automatic Control, ANSI B11.8-2001, standard provides general guidance for the design and construction of guarding (fixed, movable, interlocked movable) and safeguarding device (presence-sensing devices; two-hand control) methods, informative milling machine guarding illustrations (in Appendix A), as well as a list of recognized hazards associated with machining operations (in Appendix B). Therefore, well-designed and constructed guards or safety devices are, in many instances, feasible and prevent employee exposure to the various machine hazards, including point-of-operation hazards.

Where an employer shows that it is impossible to effectively guard or install a safety device pursuant to §1910.212 during normal production operations, an alternative measure or a combination of alternative measures must be used to protect employees. However, the employer's impossibility defense does not relieve the employer from his or her obligation to provide a safe workplace; therefore, alternative steps necessary to prevent employee injury must be taken.
[ back to text ]

4 A key element with respect to the application of the minor servicing exception is the requirement that the minor servicing activities must take place during, and it must be inherent to, normal production operations. Therefore, any servicing activity that takes place during non-production operations would be covered by the lockout/tagout standard (LOTO). [ back to text ]

5 Under the exclusive control of the employee means that the authorized employee has the authority to and is continuously in a position to prevent (exclude) other individuals from re-energizing or starting the machine or equipment while performing the servicing or maintenance activity. [ back to text ]

Standard Interpretations - Table of Contents

Thank You for Visiting Our Website

You are exiting the Department of Labor's Web server.

The Department of Labor does not endorse, takes no responsibility for, and exercises no control over the linked organization or its views, or contents, nor does it vouch for the accuracy or accessibility of the information contained on the destination server. The Department of Labor also cannot authorize the use of copyrighted materials contained in linked Web sites. Users must request such authorization from the sponsor of the linked Web site. Thank you for visiting our site. Please click the button below to continue.