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.


January 11, 1996

Mr. J.A. Hoeh, Manager
Safety and Health
Praxair, Inc.
P.O. Box 237
Keasbey, NJ 08832

Dear Mr. Hoeh:

This is in response to your March 2, 1994, letter to Roger A. Clark, former Director of Compliance Programs, requesting clarification of 29 CFR 1910.146 – Permit-required confined spaces and 29 CFR 1910.147 – Control of hazardous energy (Lockout/Tagout) standards. Our responses to your questions are in the order in which they were asked in your letter. Please accept my apology for the delay in this response.

29 CFR 1910.146 – Permit-required confined spaces (PRCS)

Question 1

If all hazards such as engulfment, hazardous gases, etc. have been removed from the permit-required confined space, but the space is a column where the potential for a fall exists would this require us to follow the full PRCS program or would either the alternate entry procedure or reclassification procedure be applicable?


If all the hazards of a PRCS (see the 1910.146(b) definition) can be and in fact are eliminated and prevented from reoccurring in the permit space, and if the fall hazard is not inherent to the permit space then reclassification procedures of paragraph (c)(7) can be applied.

We believe the (c)(5) procedures are not appropriate because they address a condition where an atmospheric hazard can only be controlled but cannot be eliminated.

Where there is potential for a fall hazard during entry or exit from the space, Subpart "D" of 29 CFR 1910 applies and fall protection will have to be provided. Even if you were to use a properly installed portable ladder, if the former contents compromised the slip resistance of the ladder rung, additional measures to prevent a fall would have to be employed.

Question 2

We have a twelve foot diameter, twenty foot high tank open to atmosphere at the top. The tank has been emptied and we enter through a bottom man-hole. The tank has atmospheric air with no contaminants. We want to cut or weld on piping within this tank. The piping contained lime slurry which has been removed and the lines purged. Would welding or cutting under these circumstances require the complete PRCS program?

NOTE: This response is based on the presumption that the tank has been classified by you as a PRCS and for some reason cannot be or has not been reclassified.


Yes, as long as the permit space retains its classification of PRCS. If the space can be reclassified using paragraph (c)(7), then the answer below applies. Also, the employer must comply with the non-permit space requirements of 1910.146.

Question 3

If a PRCS has been reclassified to a non-permit required confined space, would welding or torch work be allowed in the space?


Yes, as long as the protective measures of Subpart Q – Welding, Cutting and Brazing prevent a hazard from developing. In this case the welding standard 1910.252 addresses the hazards of welding in a confined space and therefore prevails over the 1910.146 standard as long as no other hazards are present.

You are reminded that all the protective measures of other standards are applicable to the work in this space. You are specifically directed to the following paragraphs of the Subpart Q[1910.252(a)(4)(i), 1910.252(b)(4)(i) to (vii), 1910.252(c)(4), 1910.252(c)(9), and 1910.252(c)(10)].

29 CFR 1910.147 – Control of Hazardous Energy (Lockout/Tagout)

Question 1

Does 1910.147 apply to trucks, tractors and trailers in a garage when vehicle maintenance is preformed?


Yes, the 1910.147 standard apples to trucks, tractors, and trailers (which are considered "machines and equipment") on which employees perform service and maintenance and there is potential exposure to harmful energy.

Question 2

If the standard does apply, would removal of the ignition key and chocking the wheels be sufficient to comply with the documentation exception of 1910.147(c)(4)(i)?


Except in those situations where there is a potential for injury from stored energy removal, the ignition key and disconnection of the battery cable should eliminate the potential for unexpected energization during servicing and maintenance. Chocking the wheels of the vehicle being worked on is appropriate for those situations where the power train does not prevent the vehicle from movement.

[This document was edited on 03/30/00 to strike information that does not reflect OSHA policy.]

We have included another letter on the 1910.147 standard which we trust will further shed light on the issue of servicing of motor vehicles.

If you have further questions on these requests please contact either Don Kallstrom for 29 CFR 1910.146 or Ron Davies for 29 CFR 1910.147 by telephoning (202)219 8031.

[Refer to the "Vehicle Hazardous Energy Control" Section of CPL 02-00-147 for additional policy.]


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