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.

October 27, 1995

Mr. William Taylor
ELB & Associates
605 Eastowne Dr.
Chapel Hill, N.C. 27514

Dear Mr. Taylor:

This is in further response to your letter of March 24, 1994, requesting guidance in determining whether certain spaces meet the definition of a "confined space" according to the Permit-Required Confined Spaces (PRCS) standard. Please accept our apology for the delay in this response.

Question #1 Is a sewer lift station with built in power ventilation system considered designed for human occupancy and thereby NOT a confined space? (Manufacturer's literature included with submission)

The third component in the definition is very clear for those spaces where a known or suspect hazard is considered and eliminated or controlled in the design of a workplace. When hazards are eliminated and/or managed through the application of engineering controls for the safety and health of the humans who will be occupying the space, the employee protective measures, intended by the standard, have been met.

As is the case in the literature provided, the manufacturer has considered the hazards of sewage and its by-products in the design of their pump station so humans can work in the space. Design measures such as barrier separation from the sewage, powered ventilation providing a minimum of 20 air changes an hour, automatic-on and timed (ventilation) control, lighting and even optional heating or air conditioning demonstrates that this unit was designed to accommodate the worker who will enter it.

Using or employing a pump station such as those described in the literature provided would negate the application of the 1910.146 standard for routine entries. Where system repairs would compromise the design intent, the space would have to be reevaluated per 1910.146(c)(6).

Question #2 Is a roll-off refuse container such as the 40 yard open top dumpster considered permit-required, assuming entry is over the side or through a man-way?

An open top roll-off refuse container would be considered a confined space when the second element in the standard's definition ("has limited or restricted means for entry and exit") would apply. When the doors are in a secured open position, the containers described above would not be considered a confined space either on or off the transport vehicle. For those open top roll-off containers that do not have doors, the use of a temporary stair meeting the specifications for a fixed industrial stair, securely installed, would provide an unrestricted means of entry or exit.

Question #3 Under what circumstances might dikes be considered confined spaces and, further, when would they be permit spaces?

As a containment structure, the design of a dike will determine whether it falls within the definition of PRCS standard. A dike formed of mounded or sloped earth to a height of 4 to 6 feet would not normally represent a restricted means for entry or exit. Conversely a dike formed of a vertical block or concrete wall of the same height would constitute a restricted means for entry or exit.

The determination of whether a diked area determined to be a confined space would constitute a PRCS would have to be determined based on the hazard(s) present. For example, the potential hazard of engulfment or the potential of a hazardous atmosphere from a heavier-than-air gas or vapor would have to be considered in making the determination.

Question #4 Does 1910.146 apply to rail hopper cars?

Each individual hopper of a rail hopper car should be classified as a confined space, and a permit space if their hazard characteristics fall within the scope of the standard's definitions. The activities which would most likely result in the standard's application would be associated with manufacturing, maintenance, inspection, and repair operations.

Question #5 What is an employer's responsibility and liability when the city-owned permit space on the employer's property is entered by city employees?

This response only addresses responsibility and liability from the standpoint of the Occupational Safety and Health Act and the standards developed from its authority. The employer's responsibility with respect to its duties under 1910.146 is determined in part by whether its workplace contains confined spaces. If the space is located in the employer's workplace, they have the duty under 1910.146(c)(1) to evaluate the space and determine if it is a permit-required space. If it is, but the employer decides to prohibit its employees from entering it, they shall both inform their employees of the existence of the space and take effective measures to prevent them from entering. If the space is controlled by the city and only the city arranges for city employees to enter it and only the city arranges for contractors' employees to enter it, the workplace (property) owner/employer would not be considered a "host" employer under 1910.146(c)(8).

Question #6 In a permit space where the only hazard is inwardly converging walls, can a temporary floor above the smaller cross-section area that eliminated fall potential into this area allow an employer to reclassify the space under (c)(7)? What if instead of a floor, entrants wore harness and restraint line that would not permit him to fall to bottom?

A temporary floor, installed so as to carry the anticipated total load of the authorized entrants and would-be rescuers without moving, can be a method of hazard elimination which could be employed to meet the requirements of 1910.146(c)(7). The use of a harness and restraint line in lieu of a temporary floor would not be a basis to reclassify the space because they (harness and restraint line) are a form of hazard control rather than hazard elimination.

Question #7 Where inwardly converging walls converge at a 45-degree angle to a point 4 inches in diameter, too small for someone to get stuck in, would this still be considered permit required? (attached sketch provided)

The inward converging walls alone, in the absence of any other hazard, would not render the space permit-required. The sketch clearly indicates that an entrant could not be entrapped in the 4-inch diameter cross-section, thus causing asphyxiation. However, the present of other factors such as a potentially unsafe atmosphere or engulfment, would render it permit-required.

Question #8 Is there a maximum time for which a permit can remain valid?

Yes. Paragraph (e)(4) states..."The duration of the permit may not exceed the time required to complete the assigned task or job identified on the permit in accordance with paragraph (f)(2)." Paragraph (f)(2) requires the employer to identify the purpose of the entry. In summary, the duration of the permit can only be for the time required to accomplish the task for which the permit was issued.

As an example, a permit is issued to inspect a space and the inspection determined that repair was needed. The inspection permit could not be extended to cover the repair. The reasoning behind this is to assure that all potential hazards are identified, protective measures incorporated, and evaluations performed before employees enter. That is not to say that relevant and unchanged information of the inspection permit could not be used if the issuance of the repair permit. A combination inspection/repair permit could be issued IF AND ONLY when all the potential hazards of ALL the anticipated repair activities are evaluated and addressed on the permit and during the entry procedures.

Should you have further questions on this response, please contact Mr. Don Kallstrom in the Office of General Industry Compliance Assistance at (202)219-8031.


John B. Miles, Director
Directorate of Compliance Assistance