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.

December 2, 1991

Mr. Dennis E. Palmer, P.E.
Vice President
Barr Engineering Company
7803 Glenroy Road
Minneapolis, Minnesota 55439-3123

Dear Mr. Palmer:

This is in response to your letter requesting an interpretation of the Occupational Safety and Health Administration standards addressing excavations. I apologize for the delay in responding to your inquiry.

In your letter, you asked whether distance alone was adequate to protect employees from the hazards of cave-ins. We reviewed the situation discussed in your letter and determined that at the times your employee maintained a distance of at least two times the height of the vertical sidewall from the toe of the sidewall, the employee was not exposed to the hazards of cave-in. Therefore, no additional protective system was necessary. However, when distance alone is relied upon to protect employees from the hazards of cave-in, all employees entering the excavation must be instructed not to enter the danger zone and a warning system must be provided to prevent workers from entering the danger zone inadvertently. Roping off the area or adequately marking the area with cones, flags or other highly visible means are examples of acceptable warning systems.

Please be advised that it is the responsibility of a competent person to determine, based on the conditions existing at each site, the distance away from the highwall necessary to protect the workers and the warning system necessary to adequately warn workers of the hazardous area.

If we can be of any additional assistance, please contact Roy F. Gurnham or Dale R. Cavanaugh of my staff in the Office of Construction and Maritime Compliance Assistance at (202)235-8136.


Patricia K. Clark
Directorate of Compliance Programs

April 3, 1991

Ms. Patricia K. Clark
Directorate of Compliance Programs
Room N-3471
200 Constitution Ave.
Washington, D.C. 20210

Re: 29 CFR 1910.120 Hazardous Waste Operations and Emergency Response Request for Interpretation on Site Excavation Section

Dear Ms. Clark:

Barr Engineering Co. (Barr), respectfully requests an interpretation of the Site Excavation requirement in the Hazardous Waste Operations and Emergency Response Standard [29 CFR 1910.120(b)(1)(iii)] as it relates to appropriate protective systems.

On November 20, 1990 the Peoples Natural Gas Site in Dubuque, Iowa was inspected by an Iowa OSHA Health compliance officer. The Iowa OSHA compliance officer observed the presence of sideslopes that were not in compliance with the OSHA requirements for excavations. Barr subsequently received a citation that stated:

"Near Coal Tar Tanks, Exclusion Zone-Class "C" soil of excavation area was stepped in two vertical cuts of 5 feet each. This did not meet the sloping or benching specifications for that type of soil as per 1926.651."

Barr's responsibility at the site is to observe the contractor for conformance with the plans and specifications, on behalf of the owner, and to perform soil sampling for chemical analysis and other miscellaneous work as a consultant to the owner. Barr was aware that the sideslopes cited by the Iowa OSHA compliance officer were present, and the Barr employee on-site maintained a safe distance from these sidewalls at all times while working in the excavation. Barr did not have the responsibility for the construction of these sideslopes and did not have the authority to correct the problem. Barr had informed the owner and the contractor of the presence of these sideslopes.

Because the Barr employee maintained what we considered to be a safe distance from the vertical sidewalls during the performance of his work, we believe that our employee was adequately protected from cave-in. The following paragraphs outline the methods that the Barr employee used while working at the site to protect himself from the potential danger associated with the unsafe sideslopes.

Figure 1 shows a layout of the project site. Figures 2 and 3 show a representation of the excavation and cross sections of the excavation. These figures illustrate the location of the two vertical sidewalls seen by the Iowa OSHA compliance officer who visited the site. The areas which the Barr employee considered to be safe for the work of collecting soil samples or otherwise conducting observation activities are also identified on Figures 2 and 3. To conduct Barr's work at the site it was necessary for the Barr employee to enter the excavation, however, it was not necessary to be in the immediate vicinity of the vertical sideslopes.

Typically, Barr considered that the probable distance from a vertical sidewall that may be impacted during a slope cave-in would be two times the height of any given sidewall. Therefore, to be safe from the danger presented by the vertical sidewall, the Barr employee maintained a safe distance of at least two times the height of the vertical sidewall from the toe of the vertical sidewall.

Although the OSHA Excavation Standard (29 CFR 1926 Subpart P) does not describe the use of a safe distance as a specific safety protective system to protect employees from cave-ins, it is our belief that in a large excavation, distance from an unsafe sideslope could serve as a good safety measure. Barr believes that this may have been an oversight in the promulgation of the standard.

Please review this situation and offer an interpretation on whether distance, as determined by sound engineering principles, can be used as an adequate protective measure. If you have any questions concerning the methods that the Barr employee used to protect himself or if you need further information pertaining to the conditions of this site, please feel free to contact Jim Langseth or me at (612) 830-0555. We look forward to your reply.


Dennis E. Palmer, P.E.
Vice President

DEP/mls Enclosures

November 5, 1991

MEMORANDUM FOR:     Patricia K. Clark
                   Director Directorate of Compliance Programs

ATTENTION:          Dale R. Cavanaugh 
                   Office of Construction and Maritime
                   Compliance Assistance

FROM:               John T. Phillips 
                   Regional Administrator

SUBJECT:            Comments - Draft Response to Barr Engineering

Upon review of your subject draft response letter, we are in agreement with your interpretation of a safe distance. However, we would suggest that once a safe distance has been determined, a system be provided to warn employees whenever they may inadvertently stray into the danger zone created by the vertical face. OSHA considers the assurances that determining and maintaining warning devices would fall under the responsibility of the competent person at each trench/excavation site. Some practical devices such as cones, warning lines or flags could be used to identify the potential danger to the employees.


November 4, 1991

MEMORANDUM FOR:     John T. Phillips
                   Regional Administrator

ATTENTION:          Darrell McClatchey/FSO

FROM:               Alonzo L. Griffin 
                   Area Director

SUBJECT:            Comments--Draft Response to Barr Engineering Company

The Des Moines Area Office has reviewed the proposed draft response and discussed it with the State of Iowa. Iowa's comments are as follows:

1. Iowa believes that being given one day to review and respond to these issues is not sufficient time to address the concerns raised, especially in light of the fact that National Office took six months to review these issues.

2. Iowa agrees that safe distances are one means to protect an employee (i.e., not exposed to a hazard), but sufficient analyses and design must be made to determine the safe distances as required by 29 CFR 1926.652 (c). Iowa does not feel the assumption that one is protected if one is two times the height away from the toe of a vertical excavation is sufficient unless engineering or other competent data is presented to support such a conclusion.

Iowa feels a competent person, trained to recognize the hazards and understand the standards, would be required to evaluate an excavation. This person would be required to inspect the site and change any distance requirements if conditions on the site should change (i.e., excavation equipment operating on the slope in question).

3. Iowa also feels that positive means be used to prevent entry into those excluded areas, as pointed out in comments made by Region VII.

The Des Moines Area Office comment is as follows:

The response letter should state with absolute certainty that the interpretation applies only to the situation as presented, not to situations in general.