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 http://www.osha.gov.

November 19, 1991 [Reviewed November 22, 2017]

Mr. George Kennedy, C.S.P.
Director of Safety
National Utility Contractors Association
1235 Jefferson Davis Highway, Suite 606
Arlington, Virginia 22202-3283

Dear Mr. Kennedy:

This is in response to your September 25 request for an interpretation of the Occupational Safety and Health Administration's excavation standards addressing air sampling in trenches.

Air sampling required by 29 CFR 1926.651(g) does not have to be performed in all trenches over four feet in depth. This paragraph addresses excavations over four feet deep where oxygen deficiency or other "hazardous atmosphere exists or could reasonably be expected to exist", such as in excavations in landfill areas or in areas where hazardous substances are stored nearby. It is the responsibility of a competent person to determine if air monitoring needs to be performed before employees enter each excavation.

Thank you for your interest in occupational safety and health. We hope you find this information helpful. OSHA requirements are set by statue, standards, and regulations. Our letters of interpretation do not create new or additional requirement but rather explain these requirements and how they apply to a 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 impact 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 22, 2017, and reflects current OSHA regulations and policies .]