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.

April 5, 1995

The Honorable Lincoln Diaz-Balart
U.S. House of Representatives
Washington, D.C. 20515-0921

Dear Congressman Diaz-Balart:

Thank you for your letter of February 24 concerning whether or not organic rock, such as "Miami oolite rock" should be considered by the Occupational Safety and Health Administration (OSHA) as "stable rock" for the purposes of OSHA's excavation regulations. I apologize for the delay of this response.

As you point out in your letter, the term "stable rock" is defined by OSHA to mean "natural solid mineral matter that can be excavated with vertical sides and remain intact while exposed." This definition is important because certain precautions needed to be taken to prevent cave-in hazards in other types of material do not need to be taken in "stable" rock. Your constituents are concerned that "Miami oolite rock" is an organic rock and does not meet OSHA's definition and, therefore, does not qualify for the exemption.

After discussing the matter with several soil mechanics experts, we feel it would be inappropriate to change the definition of "stable rock" to include "Miami oolite rock." Although oolite can sometimes exhibit the properties of stable rock, it is often interspersed with sand seams which are not stable. In addition, oolite rock poses a potential cave-in hazard because of the high angle of fracture that occurs when it is broken, as can happen during excavation operations. This high angle, which is not a characteristic of stable rock, can lead to a cave-in. Because of these characteristics, a blanket exception from the regulations should not be granted for oolite rock conditions. However, OSHA recognizes that protective systems are not always necessary in some soils including oolitic rock, and has provided in the regulations at 29 CFR 1926.652(b)(4) that excavations may proceed in accordance with the recommendations of a registered professional engineer. Therefore, if an engineer evaluates the oolitic rock and determines that protective systems are not necessary, then work may proceed accordingly.

I appreciate your interest in this matter. If you have any further questions, please do not hesitate to contact Mr. Roy F. Gurnham or Mr. Dale Cavanaugh of my staff in the Office of Construction and Maritime Compliance Assistance at (202) 219-8136.


Joseph A. Dear
Assistant Secretary

February 24, 1995

Mr. Joseph A. Dear
Assistant Secretary of Labor
For Occupational Safety and Health
U.S. Department of Labor, OSHA
200 Constitution Avenue, N.W.
Room 2315
Washington, D.C. 20210

Dear Mr. Dear:

I would like to bring to your attention a situation being encountered by several of my constituents.

It is my understanding that current OSHA regulation CFR 29 1926.652 requires that certain precautions be taken by underground contractors to prevent cave-ins at excavation sites except when "excavations are made in stable rock". I further understand that while mineral rock is considered stable, organic rock is not considered stable.

"Miami oolite rock", which is found throughout South Florida, is an organic rock considered by local engineers to be very stable. Because OSHA regulations do not make exceptions for this particular stable organic rock, unneeded expenses are being added to the cost of construction in Dade County Florida. Because the definition of "stable rock" is not in the text of the rule, but in an appendix, perhaps it is possible to include "Miami oolite rock" in this definition without amending the rule itself.

I would appreciate hearing from you regarding this proposal, or any other proposal you may have regarding this situation.


Lincoln Diaz-Balart