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Standard Interpretations - Table of Contents
• Standard Number: 1910.147

November 30, 2010

Mr. Jimmy Hill
Marshall Space Flight Center
Safety and Mission Assurance Directorate
QD5O/Industrial Safety Department
Marshall Space Flight Center, Alabama 35812

Dear Mr. Hill:

Thank you for your August 20, 2007 letter to the Occupational Safety and Health Administration's (OSHA) Directorate of Enforcement Programs (DEP), formerly called the Directorate of Compliance Programs. This letter constitutes OSHA's interpretation only of the requirements herein, and may not be applicable to any question(s)/scenario(s) not delineated within your original correspondence. You had specific questions regarding compliance with several OSHA standards, including 29 CFR 1910.147, The control of hazardous energy (lockout/tagout); Subpart S - Electrical, 29 CFR 1910.303, General Requirements; and Subpart S - 29 CFR 1910.333, Selection and use of work practices. Please pardon the delay in our response.

Your paraphrased questions and our responses are provided below. Several questions addressing very similar issues have been grouped together. Please note that you can find additional guidance regarding controlling hazardous energy sources at "OSHA Instruction, CPL 02-00-147, The Control of Hazardous Energy, Policy and Enforcement" at

Exclusive Control
Scenario 1: Maintenance is to be performed on a single piece of shop machinery, such as a lath or drill press. The machine has a single energy source which is a disconnect switch, located in clear view, within five unobstructed feet of the machine on an adjacent wall. An electrician placed the disconnect switch in the "off position, removed the fuses from the disconnect switch and the machine's control panel, and verified that the machine would not start. In order for another employee to reach the disconnect switch, they would need to walk past the employee performing maintenance on the machine.

Question 1: Is the disconnect switch "under the exclusive control" of the employee performing the maintenance, or is a lockout or tagout device still required to be placed on the disconnect switch?

Reply: OSHA's standard at Section 1910.147 includes provisions to protect employees performing servicing or maintenance of equipment from unexpected energization or start up. Section 1910.147(a)(2) Application, states:

(iii) This standard does not apply to the following:

(A) Work on cord and plug connected electric equipment for which exposure to the hazards of unexpected energizaton or start up of the equipment is controlled by the unplugging of the equipment from the energy source and by the plug being under the exclusive control of the employee performing the servicing or maintenance.

The exception applies only to equipment that is de-energized through a cord and plug connection, and not to other forms of energy isolation devices, such as a disconnect switch. Therefore, the disconnect switch described in the scenario above would need to be locked out and tagged out in accordance with Section 1910.147(c) through (f), as well as Section 1910.333(b)(2).

Question 2: Under the scenario above, if the machine is connected via cord and plug to a wall receptacle within five feet of the machine, and an electrician unplugs the plug from the wall receptacle, is the plug considered to be under the exclusive control of the employee?

Reply: The lockout/tagout requirements of Section 1910.147 do not apply to cord and plug connected equipment if the equipment is unplugged and the plug is in the exclusive control of the employee who is performing the servicing or maintenance of that equipment. "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 the machine or equipment during servicing or maintenance activity. See, OSHA Instruction CPL 02-00-147, The Control of Hazardous Energy - Policy and Enforcement. In the scenario you describe, the plug may not be close enough to the employee to be under exclusive control. The employee would need to be in a position to exert the degree of control necessary to prevent another employee from inadvertently plugging in the machine.

Scenario 2: An electrician is replacing the ballast on a fluorescent light. The electrician uses the light switch on the wall to de-energize the florescent light. He verifies that the light will not work after the light switch has been turned "off' before changing the ballast. The light switch is located in the room where the work is being performed and is in direct sight of the electrician. The electrician is in a position where he will know if another person tries to operate the light switch. In this scenario, electricians normally work in pairs, where one performs the work while the other stands next to the light switch.

Question 3: Is the light switch under the "exclusive control" of the electrician, or is a lockout device still required to be placed on the light switch?

Reply: OSHA's Subpart S -Electrical standard at Section 1910.333 applies to this question because it involves an employee exposed to contact with parts of fixed electric equipment or circuits. Unlike Section 1910.147, the standards in Subpart S do not include an "exclusive control" exception. Instead, Subpart S standards have their own lockout and tagging requirements for the control of hazardous energy. Specifically, Section 1910.333(b)(2), Lockout and tagging, provides that "...the circuits energizing the parts shall be locked out or tagged or both in accordance with the requirements of this paragraph ..."

In the scenario you describe, the light switch may be activated while work is being performed, as the work area is not restricted to others. Moreover, such activation can occur prior to the worker advising another entering employee that electrical work is being performed. Thus, the electrician (exposed worker) replacing the ballast would not be protected from the existing hazard designed to be guarded against (e.g., electrical).

Periodic Inspections
Scenario 3: Section 1910.147(c)(4)(i) provides that procedures shall be developed, documented and utilized for the control of potentially hazardous energy when employees are engaged in the activities covered by this section. Section 1910.147(c)(6)(i) goes on to require periodic inspection of the energy control procedure at least annually to ensure that the procedure and the requirements of this standard are being followed.

A group, whose primary function is to perform testing of hardware, has two employees who have been qualified as "authorized employees" to perform lockout of the machines when performing maintenance on any given machine.

Question 4: In order to meet the requirement in Section 1910.147(c)(6)(i)(A), can one "authorized employee," who is not performing the lockout procedures, observe/inspect a second "authorized employee" who is performing the lockout procedures?

Reply: Yes. Section 1910.147(c)(6)(i)(A) states:

"The periodic inspection shall be performed by an authorized employee other than the ones(s) utilizing the energy control procedure being inspected."

The inspector, who must be an authorized employee other than the one utilizing the energy control procedure being inspected, must observe the implementation of the energy control procedure for the servicing and/or maintenance activities being evaluated and talk with the employee implementing the procedure to determine that all the requirements of the LOTO standard are understood and being followed by the employee. The authorized employee performing the inspection may be someone who has previously implemented the energy control procedure being inspected, as long as he or she is not implementing any part of the energy control procedure while it is being inspected.

Question 5: Is every lockout procedure required to have a periodic inspection, or can lockout procedures be grouped for machines that are of similar construction and operation?

Reply: An employer may group distinct procedures associated with similar machines or equipment and consider the group of distinct procedures to be a single procedure for purposes of conducting a periodic inspection if the machines or equipment in the group have the same or similar types of control measures. Grouping energy control procedures for same or similar machines or equipment for inspection purposes may streamline the inspection and review process, since there will be a smaller number of procedure groups than individual procedures. Thus, an employer may elect to group procedures as described above, and then inspect a representative number of such employees implementing one procedure within each group. This approach is acceptable as long as the inspection sampling reasonably reflects plant servicing and/or maintenance operations and hazardous energy control practices for the procedure being inspected.

Question 6: Is the periodic inspection of a lockout procedure required to be performed while the actual lockout sequence is being performed, or can it be a review of the written lockout procedure with the "authorized employee" at a later date?

Reply: The periodic inspections must contain at least two components: 1) an inspection of each energy control procedure, and 2) a review of each employee's responsibilities under the energy control procedure being inspected. Each energy control procedure must be separately inspected at least annually to ensure that the energy control program is being properly utilized. At a minimum, these inspections must provide for the demonstration of the procedures and must be performed while authorized employees perform servicing and/or maintenance activities on machines or equipment.

Explicit Use of Lockout/Tagout Equipment
Scenario 4: A machine is scheduled to be removed from the site. An electrician turns the disconnect switch to the "off' position and applies the company's standardized lockout device while he disconnects the power supply cables from the machine. The machine is removed from the site and no other equipment is connected to the disconnect switch. To keep it from being operated, the electrician leaves the standardized lockout device attached to the disconnect switch. This arrangement might be in place for an indefinite period of time, although no maintenance work is to be performed.

Question 7: Can the employer's standardized lockout device be used, or is this a violation of "shall not be used for other purposes," since no one is actually performing maintenance and the lockout devices are basically being used as a "configuration lock" to maintain the configuration disconnect switch?

Reply: OSHA's standard at Section 1910.147(c)(5)(ii) states:

"Lockout devices and tagout devices shall be singularly identified; shall be the only devices(s) used for controlling energy; shall not be used for other purposes;..."

OSHA considers the lockout device described above as being used for hazardous energy control purposes for this entire period. Thus, this practice is not prohibited by Section 1910.147(c)(5)(ii).

Generic Lockout/Tagout Procedures
Scenario 5: A company develops a generic energy control procedure for machines that are similar in operation, construction, and have a single power source (e.g., air handling unit).

The procedures include data requirements, such as the type and location of the machine, as well as: 1) the purpose of the procedure; 2) the authorization; 3) type of energy sources to be isolated; and 4) a general sequence of shut-down and start-up.

Question 8: If a machine is powered by a single source, does the energy control procedure require more detail, or can they be as simple as addressing only the steps defined in Section 1910.147(d)(1)-(d)(6) and (e)(1)-(e)(3)?

Reply: OSHA's standard at Section 191 0.147(c)(4)(ii) states:

"The procedures shall clearly and specifically outline the scope, purpose, authorization, rules, and techniques to be utilized for the control of hazardous energy, and the means to enforce compliance. This means that, at a minimum, the procedures must include the following elements including, but not limited to, the following:

A. A specific statement of the intended use of the procedures;
B. Specific procedural steps for shutting down, isolating, blocking, and securing your machines or equipment to control hazardous energy;
C. Specific procedural steps for the placement, removal, and transfer of lockout devices and the responsibility for them; and
D. Specific requirements for testing a machine or equipment to determine and verify the effectiveness of lockout devices or tagout devices, and other energy control measures."

The procedure would need to contain enough detail for authorized employees to have a clear understanding of the energy control measures so that the employees can follow the employer's established procedures for a machine LOTO to effectively control all types and forms of hazardous energy.

Question 9: If the energy control procedure includes the sequence of steps to shut-down; place in a safe working condition; apply lockout and verify the effectiveness of devices; and the sequence of steps to remove the lockout device and re-energize the machine, must the procedure also include all the necessary steps to perform the actual maintenance?

Reply: No. Based on the language in Section 1910.147(c)(4)(ii), the steps needed to perform the maintenance are not required to be included in the energy control procedure.

Clearances near Electrical Panels
Scenario 6: A tool box that is 36 inches in height and mounted on wheels is temporarily placed in front of a 277-volt lighting panel. The placement of the tool box does not prevent anyone from gaining access to the light panel to operate lighting breakers. The tool box can easily be moved to provide the clear working space for an authorized employee to service the lighting panel in accordance with 29 CFR 1910.303 (g)(1)(i).

Question 10: Can the tool box be temporarily placed in front of the lighting panel?

Reply: No. The minimum required distances for work space clearance that must be maintained in front of live parts are listed in Table S-1 of Section 1910.303 (g)(1)(i)(C), which elaborates on the clear spaces requirement for such working spaces. This access and working space shall be kept clear at all times for operation and maintenance personnel and may not be used for intermittent/incidental storage of nonpermanent equipment or furniture, which could interfere with ready access to the electric equipment in the event of an emergency. If access is difficult, or if obstacles must be moved, the, resultant delay might allow a minor problem to become a major hazard. This issue was reviewed in a similar situation in an interpretation letter dated May 28, 1999 and may be found on OSHA's website at under standard interpretations, 1910.303(g)(1)(i) for further reference.

Circuit Breakers listed as "Spare "
Scenario 7: During an inspection of a laboratory, it is determined that several circuit breakers are labeled "spare" in an electrical panel, but are in the "on" position. The inspector does not know whether the circuit breakers are actually providing power to a load, or whether they have been accidentally turned "on."

Question 11: Is it a violation of Section 1910.303(f) if a circuit breaker in an electrical panel is labeled "spare," but is in the "on" position, since one would not know if the spare circuit breaker is actually providing power to an unknown load?

Reply: Section 1910.303(f)(2) states:

"Each service, feeder, and branch circuit, at its disconnect means or over current device, shall be legibly marked to indicate its purpose, unless located and arranged so that the purpose is evident."

Based on your scenario, each circuit breaker is legibly marked to indicate its purpose. However, it would be a violation of the standard if the circuit breaker identified as "spare" fed wiring since the label would be inaccurate.

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 If you have any further questions, please feel free to contact the Office of Federal Agency Programs at (202) 693-2122.


Thomas Galassi, Director
Directorate of Enforcement Programs

Standard Interpretations - Table of Contents

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