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NOTICE: This is an OSHA Archive Document, and may no longer represent OSHA Policy. It is presented here as historical content, for research and review purposes only.

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

January 14, 2003

Richard S. Jones, P.E.
TriTex Technologies, Inc.
4611 Langland Road, Suite 104
Dallas, Texas 75244

Dear Mr. Jones:

Thank you for your September 19, 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 or questions not delineated within your original correspondence. You had questions regarding the Control of hazardous energy (lockout/tagout) standard, 29 CFR 1910.147. Specifically, you provided excerpts from a client's lockout/tagout procedures because the client is confused about the requirement to produce a procedure for every valve, pump, compressor, etc. Your scenario, questions, and reply follow:

Scenario: Assume a processing complex has 15,000+ valves. Of these 15,000+ valves, there are basically two families of valves: 1) control valves, and 2) block valves. Within these two classifications, there may be both actuated and non-actuated valves comprised of a dozen or so different types of valves, such as the gate valve, check valve, globe valve, ball valve, plug valve, butterfly valve, needle valve, angle valve, etc.

The following sample procedural excerpt for control valves from our client's Guidelines for the Lockout/Tagout of Equipment illustrates the type of procedure used for these 15,000+ valves:

Control Valves



  1. Identify the flow rate through the control loop
    1. Look at the flow meter next to the control
  2. Start closing the up-stream block valve slowly
  3. Maintain the same flow rate through the flow loop by opening the by-pass as the block valve is closed
  4. Inform the operator that the control is by-passed
  5. Close the down stream block valve to isolate the control from the process flow
  6. Slowly bleed all the liquid or gas from the control loop
    1. Bleed any pressure to the appropriate disposal location
    2. Have the operator open the control valve if the bleeders on each side of the control are not available
  7. Lockout/Tagout all possible sources of energy from the control loop 1
    1. Lock and tag the upstream block valve
    2. Lock and tag the downstream block valve
    3. Lock and tag the control valve activating energy source (air, electricity, hydraulic, etc.)
  8. Obtain all the necessary safety permits (cold work, hot work, entry, etc.)

    Additionally, you provided specific lockout/tagout procedural guidelines for electric and steam driven pumps, reciprocating and centrifugal compressors, heaters/furnaces, boilers, and vessels.

Question: Does the lockout/tagout standard require procedures for every single piece of equipment or is a procedure for each type of equipment sufficient?

Reply: No, energy control procedures are not required for every single piece of equipment if certain criteria are met. Similar machines and/or equipment (those using the same type and magnitude of energy), which have the same or similar type of controls, can be covered with a single procedure. However, the procedure must be written in sufficient detail and provid enough direction so that the employees can follow the procedure and determine how to safely perform servicing or maintenance work. Over-generalization can result in a document that has little or no utility for employees who must follow the procedure.

Paragraph 1910.147(c)(4)(ii) states, in part, that the required documentation must clearly and specifically outline the scope, purpose, authorization, rules, and techniques employees are to use to control hazardous energy, and the means to enforce compliance. During an inspection, OSHA will carefully examine the energy control procedure of any employer claiming that a single comprehensive procedure is sufficient throughout its workplace in order to ensure that a single procedure is indeed adequate.

While the Agency does not insist on multiple procedures, a procedure that addresses multiple machines or pieces of equipment must include the above referenced paragraph (c)(4)(ii) requirements (e.g., purpose, scope of machines/equipment to be covered) and a statement as to its intended use. Nevertheless, in order to be covered by one procedure, the various pieces of machinery or equipment, at a minimum, must have the same:





  1. Specific procedural steps for shutting down, isolating, blocking, and securing machine or equipment to control hazardous energy;
  2. Specific procedural steps for the placement, removal, and transfer of lockout or tagout devices and the responsibility for them; and
  3. Specific requirements for testing a machine or piece of equipment to determine and verify the effectiveness of lockout/tagout devices and other control measures.

Your eight-step sample procedure alone appears to lack the detail necessary to comply with all of the 1910.147(c)(4)(ii) provisions; there appears to be insufficient information for employees to implement specific control measures necessary to safely perform the servicing and maintenance work. In short, the number of variables and associated risk involved with controlling hazardous energy in a processing complex with 15,000+ control valves necessitate a careful hazard analysis to permit an understanding of the job specific hazards and the specific method or means (specific control measures) to control the energy (see 1910.147(d)(1)) . It is important to emphasize that a thorough hazard analysis provides the foundation for developing, documenting, and implementing hazardous energy control procedures.

For example, a control system bypass task is significantly different from a process system lockout/tagout. In this latter scenario, employees need to know much more than the lockout/tagout steps for a specific type of equipment component, such as a control valve, in order to perform an orderly and safe shutdown. Simply listing the control valve steps without the proper preparation for the specific process system (e.g., identifying which valve(s) require isolation and the associated shutdown order) to be worked on may lead to confusion and error due to inadequate employee direction. The lack of procedural clarity and over-generalization could result in the employees failing to isolate key control valves, resulting in their exposure to the hazardous energy during the servicing or maintenance work.

Some employers utilize manufacturer guidelines (e.g., operational/maintenance manuals) that are referenced in and linked to generic lockout/tagout procedures in order to provide employees with specific steps for controlling hazardous energy associated with equipment and machines. For example, your client may decide to link their control valve guidelines as part of a specific job procedure after a hazard analysis has been performed and the safe energy control sequence determined. These control valve guidelines or supplemental methods, such as using checklists, placards, work authorization permits, may provide an effective means to augment generic lockout/tagout rules and techniques, by addressing the specific sequential steps to control the hazardous energy associated with various servicing or maintenance projects.

Furthermore, the company procedure must specify that the employees are required to perform their work in accordance with the terms and limitations of the general lockout/tagout policy and the augmented checklist or work permit system. The checklist or permit would need to identify the equipment to be serviced or maintained, the types and unique energy characteristics to be encountered, methods for safe work, and the process or procedures to be used to accomplish the task safely.

Question: Is it acceptable to prepare a lockout/tagout procedure for the two general classifications of valves, or for the dozen or so types of valves, or is it the intent of OSHA to prepare lockout/tagout procedures for all 15,000+ valves?

Reply: As described above, this performance-oriented standard allows a degree of latitude to the employer to "tailor" the required procedures to fit the individual conditions of the workplace. However, a plant-wide approach for controlling hazardous energy that is based on system components (e.g., valves), rather than thorough process-specific equipment/machine hazard analyses, may be seriously flawed. The standard contemplates the control of hazardous energy associated with machinery and equipment; hence, a focus on system components often will not provide sufficient employee guidance regarding: (1) the various types and magnitude of hazardous energy; or (2) all of the means to effectively control the hazardous energy on the various pieces of machinery and equipment.

Question: Would the same procedural requirements (as stated above) apply to other common and redundant equipment such as pumps, compressors, heaters, furnaces, boilers, and vessels?

Reply: Yes. With regard to your client's equipment procedures (valves, pumps, compressors, heaters/furnaces, boilers, vessels), our office has not performed a detailed review for all of the procedures you provided, since the Agency does not review energy control procedures in this manner or certify that such procedures comply with the provisions of the lockout/tagout standard. OSHA does not test, approve, certify, or endorse any procedure, equipment, or product.

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 haveany 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





1The control valve procedure's hazardous energy control steps were not performed in the proper sequence as the:





  1. Residual energy was released (Step F) prior to the application of the lockout/tagout device application (Step G); and

  3. Specific measures to verify isolation and de-energizationwere not identified and designated to take place after the stored energy was dissipated (Step F). Furthermore, verification of isolation, depending on the process specific energy control application, may need to be continued while the servicing and/or maintenance work is underway or until the possibility of such accumulation no longer exists.

  5. Step G.3 has employees lock and tag the activating energy source without any previous guidance in terms of shutdown preparation, shutdown, and isolation procedures. After the air, hydraulics, and/or electric energy sources are locked/tagged out, then the stored energy [1910.147(d)(5)] and verification of isolation [1910.147(d)(6)] steps must be implemented.

See 1910.147(d) for the application of control sequence requirement. [ back to text ]