Design and use of trench shields and manhole boxes

November 7, 1991 [Reviewed November 8, 2018]

Mr. Robert Kundel
President
Kundel Industries, Inc.
[Recipient address omitted]

Dear Mr. Kundel:

This is in response to your inquiries concerning the Occupational Safety and Health Administration's (OSHA) regulations addressing the design and use of trench boxes, and whether round steel pipes may be used as manhole boxes. We apologize for the delay in our response.

In regard to your question concerning a trench shield which needs to be tied to the ground (i.e., driven by force into the ground) in order to reach its full capacity, please be advised as follows: such a system may be used if it has been designed and approved by a registered professional engineer, and used in accordance with that design. The depth rating would be determined by the engineer. (See 29 CFR 1926.652(c)(4).)*

In regard to the example you gave as part of the above question, please be advised that 29 CFR 1926.652(g)(1)(iv) states: "Employees shall not be allowed in shields when shields are being installed, removed, or moved vertically." In addition, in the example you give, the employee shall not be allowed in the shield when it is moved horizontally because the shield would not have the requisite depth capacity.

In regard to your question whether it would be acceptable to use a round 8 1/2 foot outside diameter, 1/4 inch thick steel pipe for a manhole box if "there is uniform pressure", please be advised that such a system may be used if the system has been designed and approved by a registered professional engineer and used in accordance with that design.

In regard to your question concerning stacked trench boxes, please be advised that when boxes are stacked in an excavation, they do not all have to be designed to resist the forces calculated for the deepest part of the trench. The standard only requires that the boxes be used at a depth not greater than that for which they are designed. (See 29 CFR 1926.652(g)(1)(i).)* To facilitate proper stacking in deep excavations, a design or system should be used to prevent the boxes from being misplaced in the excavation when boxes of different ratings are used. Designing the boxes so they will fit together only one correct way, or using a marking system that readily identifies the maximum depth each individual box can be placed, are examples of systems that could be used to prevent such misplacement.

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 letters of interpretation do not create new or additional requirements but rather explain these requirements and how they apply to particular circumstances. This letter constitutes OSHA's interpretation of the requirements discussed. From time to time, letters are affected when the Agency updates a standard, a legal decision impacts a standard, or changes in technology affect the interpretation. To assure that you are using the correct information and guidance, please consult OSHA's website at https://www.osha.gov. If you have further questions, please feel free to contact the Directorate of Construction at (202) 693-2020.*

Sincerely,
Patricia K. Clark, Director
Directorate of Compliance Programs

*[This letter has been modified (non-substantive changes) on November 8, 2018, and reflects current OSHA regulations and policies.]