Thursday, October 24, 2013

Sloping & Benching systems for excavations

May 2, 2013

Dear Mr. C***:

Thank you for your August 23, 2012 letter to the Occupational Safety and Health Administration (OSHA). We apologize for the delay in our reply. 

As you know, the State of California administers its own safety and health program under a plan approved and monitored by the Federal Occupational Safety and Health Administration (OSHA). As part of that program, the California Occupational Safety and Health Administration (Cal/OSHA), as part of the California Department of Labor, is responsible for the enforcement and interpretation of occupational safety and health regulations in that State. You may reach Cal/OSHA at:

Division of Occupational Safety and Health
1515 Clay Street, Suite 1901
Oakland, California 94612
Phone: (510) 286-7000
Fax: (510) 286-7037

Federal OSHA regulations governing sloping and benching systems for excavations

Your August 23, 2012 letter and subsequent discussions with Directorate of Construction (DOC) staff raise two specific questions regarding OSHA's excavation standard. This letter constitutes OSHA's interpretation of only the requirements discussed and may not be applicable to any question not delineated in your original correspondence. 

We have paraphrased your questions as follows:
Question 1: If the employer elects Option (4) of 29 CFR 1926.652(b) to provide the protective system for his excavation, and he retains a registered professional engineer (RPE) to design the slope and bench configurations, is the RPE design bound by the requirements and provisions of Appendix B to Subpart P of Part 1926 -- Sloping and Benching?

Response 1: No. 29 CFR 1926.652(b)(4) Option (4) - Design by a registered professional engineer, provides that:
  1. Sloping and benching systems not utilizing Option (1) or Option (2) or Option (3) under paragraph (b) of this section shall be approved by a registered profession engineer.
  2. Designs shall be in written form and shall include at least the following:
    1. The magnitude of the slopes that were determined to be safe for the particular project;
    2. The configurations that were determined to be safe for the particular project; and. . .
In addition, the preamble to the final rule of 29 CFR 1926.652(b)(4) Option (4) (54 FR 45929; October 31, 1989) further explains that:
Under this option . . . It provides no specific restrictions as to maximum allowed slopes or configurations that a registered professional engineer might design or approve . . . slopes steeper than those allowed under the other options could be used. Configurations different from those allowed under the other options could also be used.
Question 2: The employer's RPE specified the soil as Type A and designed a sloping and benching configuration for an excavation 14 feet deep. It consists of 3 feet unsupported vertical sides at the lower portions of the excavation and 11 feet sloped cuts with ¾ horizontal to 1 vertical at the upper portion of the excavation. In addition, in your September 14, 2012 discussions with DOC staff, you indicated that the excavation for the particular project is intended to station (house) the pile driving equipment. Is this configuration in compliance with the excavation standard?

Response 2: OSHA is precluded from approving or endorsing specific products, services, or analyses. The variable working conditions at job sites and possible alteration or misapplication of an otherwise safe piece of equipment, service, or system, could easily create a hazardous condition. However, where appropriate, we try to give some guidance to help employers assess whether products, services, or analyses are appropriate to use in light of OSHA requirements. 

The employer's RPE must consider site and environmental conditions, specifically taking into account the stresses that vibrations cause. It is not clear that this RPE configuration takes the vibrations into account, as it specifies "Type A" soil. "Type A" is defined in Appendix A to Subpart P of Part 1926 - Soil Classification, Section (b) Definitions:
Type A means cohesive soils with an unconfined compressive strength of 1.5 ton per square foot (tsf) (144 kPa) or greater. . . . However, no soil is Type A if:
  1. The soil is fissured; or
  2. The soil is subject to vibration from heavy traffic, pile driving, or similar effects; or . . .
Thus, even if a soil has an unconfined compressive strength of 1.5 tsf or greater as Type A, but if this soil is subject to vibration, such as pile driving activities, the soil cannot be considered as Type A. Therefore, this RPE configuration may not be appropriate for the intended use of the excavation, and may need to be modified.

No comments:

Post a Comment