Archive Notice - OSHA Archive

NOTICE: This is an OSHA Archive Document, and may no longer represent OSHA Policy. It is presented here as historical content, for research and review purposes only.

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

November 18, 1975

Mr. William F. Driskill
Assistant Executive Director
The Associated General
Contractors of America, Incorporated
1330 Mercantile Bank Building
Dallas, Texas 75201

Dear Mr. Driskill:

This is in response to your letter of July 18, 1975, addressed to Mr. C. R. Holder, requesting clarification of certain Construction Standards. It also confirms your telephone conversation with a member of my staff.

Most of your requests for clarification of excavations, trenching, and shoring standards have no clear-cut answers. This is unfortunate in some respects and future revisions relating to trenching and excavations standards shall be addressed to more definite wording.

I will attempt at answer each question in the same numerical order as asked.

(1) 1926.652(c) - Solid limestone or granite does not meet the accepted definition (geological) of soil, not withstanding OSHA's definition of "hard compact soil" in 1926.653(h).

Table P-1. - Limestone or granite may require shoring if certain conditions prevail. Such determination must be a job-site determination on an, "as found at time of exposure" basis.

(2) OSHA does not have a definition of what "average soils" are in its standards. As used in Table P-1 "average soils" appears to be between compacted angular gravels and compacted sharp sand. Inversely, from Table P-1, "average soil" has an approximate angle of repose of 45o.

(3) 1926.651(c) - OSHA considers "danger from moving ground" to ground that is "at rest" and can by some reasonable cause change its location. Some reasonable causes may be: possible variation in water content of the ground; changes in ground from exposure to air, sun, water, or freezing; loading imposed by structures, equipment, overlying material, or stored material, and vibrations from equipment, blasting, traffic, or other sources.

(4) 1926.652(e) - The only answer that OSHA can offer to your allegation that "this section is used in many citations when an employer is accused of not shoring" is that the Area Director that issued the citation concluded that evidence warranted an alleged violation of this standard. Every employer is required to take certain precautions prior to opening an excavation. This may not involve shoring or bracing. That is the reason for the word "additional".

(5) 1926.50(c) - OSHA considers "reasonable accessible in terms of time and distance" to be based on several factors, including the work hazards, the consulting physician's opinion, highway traffic etc. Each situation would have to be evaluated separately.

If I may be of further assistance, please feel free to contact me.


John K. Barto, Chief
Division of Occupational Safety Programming