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 https://www.osha.gov.

February 8, 1996

Ms. Remi Morrissette
Vermont Yankee Nuclear Power Corporation
P.O. Box 157
Governor Hunt Road
Vernon, VT 05354

Dear Ms. Morrissette:

This is in response to your letter of June 23, requesting guidance in determining whether certain spaces would be considered confined spaces by applying the Permit-Required Confined Spaces (PRCS) standard's definition. Please accept our apology for the delay in this response.

Your letter said that the entrance to the primary, containment area is through a personnel airlock that requires closing one door before opening the inner door. You asked, "Would OSHA consider this entry way a restricted or limited means for entry or exit as defined for a confined space?"

Yes. If the airlock doors are so arranged as to prohibit both doors from being maintained in an open position at the same time, an employee within the space cannot walk out of the space without restriction. Thus, entry and egress are restricted according to the standard's definition of "confined space." (We assume, based on the information in your letter, that the primary containment chamber meets the remaining two elements of the confined space definition.)

The fact that a space is considered a confined space by 29 CFR 1910.146 does not automatically mean that the space is a permit-required confined space. Since the chamber, however, is normally inerted with nitrogen, it appears that a permit-required confined space condition exists (has potential to contain a hazardous atmosphere) even though the nitrogen is purged with air before maintenance activities.

The following comments are provided under the presumption that the containment chamber is a permit space and that the only hazard is that of oxygen deficiency.

The containment chamber must be isolated from the source of the nitrogen. Some acceptable methods are blanking or blinding the line feeding the chamber, breaking or misaligning the line leading to the chamber, a double block and bleed system installed between the nitrogen source and the chamber. If the Nuclear Regulatory Commission's requirements would not allow isolating the chamber, then an equally safe alternative will have to be used. Any such alternative would have to be approved as a variance. The local OSHA Regional Office can provide guidance on the variance procedures and applicable regulations.

Regional Administrator
133 Portland Street, 1st Floor
Boston, MA 02114
617 565-7164

If the atmospheric hazard is eliminated and there is no potential for it to develop further, the space can be reclassified as a "non-permit confined space."

Your letter indicated that you can monitor oxygen concentrations in the chamber without having to enter and that you have an entry policy prohibiting entry if oxygen concentrations fall below 19.5 percent. Our concern is whether the non-entry monitoring can assure that all the areas within the chamber where the employees can and will be working are above 19.5 percent oxygen concentration (no pockets where the level will be significantly below 19.5 percent). If the chamber oxygen monitoring system cannot eliminate the possibility of nitrogen pocketing, then full permit entry will have to be carried out until actual worksite testing of the atmosphere proves oxygen levels to be non-hazardous.

All planned maintenance activities or maintenance activities that become necessary during the refueling shutdown must be reviewed for their potential to introduce hazards into the chamber that would create a permit-required scenario. Where a maintenance activity has a potential for introducing a hazard, policy and procedures must be developed to limit the hazardous element so a permit-required condition cannot develop.

If you have further questions on this response, please contact [the Office of General Industry Compliance Assistance at (202) 693-1850]. Again, please accept our apology for the delay.


John B. Miles, Jr., Director
Directorate of Compliance Programs