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Standard Interpretations - Table of Contents
• Standard Number: 1910.146; 1910.147; 1910.147(d)(5)(ii)

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.

April 18, 2007

Mr. Mark A. Gintner
COMTEC International, Inc.
P.O. Box 7184
Kennewick, WA 99336-0616

Dear Mr. Gintner:

Thank you for your August 30 letter to the U.S. Department of Labor's Occupational Safety and Health Administration (OSHA). Your letter has been referred to OSHA's Directorate of Enforcement Program's Office of General Industry Enforcement for an answer to your questions regarding OSHA's standards for Permit-Required Confined Spaces (PRCS) and Control of Hazardous Energy, 29 CFR 1910.146 and 29 CFR 1910.147. Your scenario and questions have been restated below for clarity.

Scenario: A steam generation facility produces and distributes steam at 135 psi gauge to a number of facilities for heating, humidity control, and processes. All the steam distribution piping is below grade. Access to valves, traps, and system components is through a number of steam vaults or pits located at points along the distribution grid. The valves are for facility supply and sectionalizing the system for flexibility when repairs are required. The pits are open topped with grating, and the main sectionalizing and building valves have reach rods for above ground manipulations. The pits have condensate piping in [them] running parallel to the steam system. The condensate system operates at approximately 15 psi gauge. All of these steam pits have been designated by the employer as permit-required confined spaces. Air quality is checked before and during entry and all other requirements are implemented.

29 CFR 1910.146 Questions

Question 1a: With the steam system charged and at steady state condition, is there an engulfment hazard for entrants who operate components such as valves on the pressurized steam system within the steam pit?

Reply 1a: Within the PRCS standard, the term "engulfment" means the surrounding and effective capture of a person by a liquid or finely-divided (flowable) solid substance that can be aspirated to cause death by filling or plugging the respiratory system or that can exert enough force on the body to cause death by strangulation, constriction, or crushing.

An engulfment hazard does not appear to be presented by your scenario. However, steam constitutes a recognized serious safety hazard. While mechanically and structurally sound continuous runs of steam piping would not present the potential hazard of sudden pressure releases of steam at 135 psi gauge, sudden pressure releases can occur at steam system components such as flanges and valves. Therefore, opening these valves in the steam pits, without following proper isolation procedures, is potentially hazardous. The PRCS standard requires that the hazard be isolated and defines isolation as "the process by which a permit space is removed from service and completely protected against the release of energy and material into the space by such means as: blanking or blinding; misaligning or removing sections of lines, pipes, or ducts; a double block and bleed system; lockout or tagout of all sources of energy; or blocking or disconnecting all mechanical linkages." Under §;1910.146(b), double block and bleed means "the closure of a line, duct, or pipe by closing and locking or tagging two in-line valves and by opening and locking or tagging a drain or vent valve in the line between the two closed valves."

Question 1b: Is there a hazard if the entrant only performs surveillance activities inside the vault?

Reply 1b: A potential hazard is present as explained in the response above.

Question 1c: Does the steam system need to be isolated before pit entry, or is there another option?

Reply 1c: The system would have to be isolated in accordance with the standard. As noted above in the reply to question 1a, there are different options available.

Question 1d: Does the pressurized condensate system represent an engulfment hazard?

Reply 1d: Possibly, but there is not enough information provided in your letter to reply more definitively.

Question 2: If a steam trap, valve, or other component needs to be replaced, requiring its removal from the pressurized steam system, is there a potential hazard?

Reply 2: Yes. See the reply to question 1a.

Question 3: Is sectionalizing, recharging, or positioning drain valves for isolating/depressurization still a hazard?

Reply 3: Yes. See the reply to question 1a.

Question 4: If steam drain valves discharge into the space, is that an engulfment hazard?

Reply 4: Possibly, if the discharge is liquid and has the capacity to surround and effectively capture an entrant. Additionally, a thermal hazard, due to the high temperature water or steam, would be present.

Question 5: If the steam drain valves discharge is piped outside the pit, is there still an engulfment hazard?

Reply 5: If the discharge cannot collect in the pit, then there would be no engulfment hazard in the pit.

Question 6: At what steam system pressure/temperature is double valve isolation required for work on systems in steam pits?

Reply 6: OSHA's permit-required confined spaces standard is a performance-oriented standard and does not set specific pressures or temperatures to trigger its isolation requirements. Note that isolation may be required for some systems not merely because of the temperature or pressure of the materials within, but also due to the toxicity or flammability, for example, of the material.

29 CFR 1910.147 Question

Question 1: At what steam system pressure/temperature is double valve isolation required for above ground work?1

Reply 1: Section 1910.147 is a performance-oriented standard and, as such, does not contain specific temperature or pressure criteria. Rather, the lockout/tagout standard applies in cases where energy (e.g., thermal energy) may be released in quantities or rates that could injure employees during the servicing and maintenance of machines or equipment. This standard does not apply to energy that is not hazardous. However, the standard contains a requirement for continued verification of isolation if there is a possibility that hazardous energy may reaccumulate — pursuant to §1910.147(d)(5)(ii). The likelihood of hazardous energy reaccumulating is greater when a single valve is used for control purposes, rather than a double block and bleed form of isolation.

As you may be aware, the State of Washington operates its own occupational safety and health program under a plan approved by Federal OSHA. Under this plan, the Washington Department of Labor and Industries promulgates and enforces occupational safety and health standards under authority of State law, and posts them on its website at http://www.lni.wa.gov/Safety/default.asp. Although many of Washington's standards are different, both its standards and interpretations must be at least as effective as Federal OSHA's. For information on the Washington Permit-required Confined Spaces standard and its enforcement, we suggest that you contact:
Mr. Steve Cant, Assistant Director
Washington Department of Labor and Industries
Division of Occupational Safety & Health (DOSH)
P.O. Box 44600
Olympia, Washington 98504
Telephone: (360) 902-4200
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. In addition, 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 OSHA encourages the use of a double block and bleed isolation method for LOTO purposes as it is a recognized Best Practice. With respect to the lockout/tagout standard, the use of double valve isolation is not required since the standard's energy control provisions differ from the permit-required confined spaces isolation requirements. Thus, the hazardous energy associated with the above ground steam system would need to be controlled in accordance with requirements contained in Section 1910.147.[ back to text ]

Standard Interpretations - Table of Contents

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