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.

August 30, 1991

Mr. John A. Pompei, Administrator
Oregon Occupational Safety & Health Division
Department of Insurance and Finance
21 Labor and Industries Building
Salem, Oregon 97310

Dear Mr. Pompei:

Your letter, dated December 7, 1990, to Mr. James Lake, Regional Administrator, Occupational Safety and Health Administration (OSHA), requesting interpretation of Section (g)(6) and (g)(7) of Appendix D to Subpart P, 29 CFR 1926 has been referred to the Office of Construction and Maritime Compliance Assistance for reply. We apologize for the inordinate delay of this response and regret any inconvenience that the delay may have caused.

In regard to your request for clarification of the proper spacing and placement of vertical hydraulic shoring member, prudent engineering practice would generally dictate that not more than one half of the allowable maximum horizontal spacing between vertical shores would be acceptable as the spacing between the end of the trench and the nearest vertical shore. Local soil structure and composition, however, determine the actual spacing and, subsequently, the required number of shores for a given length of trench, the degree of sloping of the ends, and any other safeguard that may be necessary to protect the worker. The footnotes and general notes to the Appendix are minimum requirements and should not be interpreted as listing all the safeguards or information needed to protect employees working in trenches.

In regard to your question concerning the bending strength of plywood, please be advised that the plywood size requirement listed in Appendix D, paragraph (g)(7) was derived to adequately control sloughing of the trench face in certain type B soils. Any correlation between the bending strength of the plywood sheeting used in aluminum hydraulic shoring systems and the bending strength of the structural members of other shoring methods is coincidental.

In regard to your question concerning the used of non-structural sheeting when it is not required by the regulations, please be advised that such additional sheeting would not be subject to the requirements of the regulations. However, the presence of such sheeting is likely to be interpreted as an indication that Type A soil or Type B soil that does not require sheeting are, in fact, not present. The sheeting is likely to be seen as an indication that other Type B soils or Type C soil is present and an inferior sheeting system is in place. Consequently, appropriate soil classification test results should be maintained by the contractor to minimize such misinterpretations.

If we can be any further assistance, please contact Mr. Roy Gurnham, Director, Office of Construction and Maritime Compliance Assistance on telephone number (202) 523-8136.


Patricia K. Clark, Director
Directorate of Compliance Programs