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Publication: November 2005. For information about changes, please see the Revision History.

Chapter 11: Excavation Safety

note: This chapter is currently being revised. See Chapter 11 Review for status and information on the update.

Overview

Excavations are defined generally as "operations where contact with soil is expected, such as trenching, removing soil to install foundation footings or exposing underground pipes for repair/replacement" (see Definitions). This chapter sets forth the practices and permit requirements for all trenches and excavations.

The implementation of the requirements of this chapter represent the best available management practices in excavation safety. These requirements will reduce the risk of a subsurface strike to the lowest practical level but cannot eliminate it altogether.

Hazards/Impacts

The most common hazards associated with excavations, in addition to those posed by working with heavy and mechanical equipment, are

• Unidentified or misidentified utilities
  Workers may be exposed to hazards such as electric shock, suffocation, or explosions if they unexpectedly come in contact with utility lines.
• Hazardous atmospheres
  Workers may be exposed to hazards such as suffocation, chemical exposure, or explosions, if they enter excavations with hazardous atmospheres.
• Cave-ins
  Worker injury or structural damage may result from sidewalls of excavations caving in.
• Structural instability
  Structures may become unstable if excavation occurs below the base of building or equipment pad foundations, or below retaining wall footings.
• Water accumulation
  Water accumulation in excavations can cause sloughing of excavation sidewalls, resulting in unsafe conditions for those entering the excavation, particularly if the use of electrical equipment is required.
• Lack of egress
  Workers may become injured while exiting an excavation if egress is not adequate, particularly if an emergency evacuation is required.
• Falls
  Workers or passersby may accidentally fall into an open, unprotected excavation, or vehicles may accidentally be driven into an uncovered or inadequately barricaded pit.

Additional potential hazards and impacts at SLAC are

• Contact with materials affected by chemicals or radiation
  Disturbing materials that contain chemical constituents from past SLAC activities and/or may be radioactive as a result of accelerator operations could pose risks to workers handling the soil and to the environment.
• Disruption of radiation shielding
  Soil and concrete are used as radiation shielding for accelerator operations. Excavations that alter or remove shielding materials could result in increased worker exposures.
• Environmental impacts
  In addition to potential contact with affected materials, excavating and grading can affect air and water quality and biological resources.

Scope

The excavation safety program and its requirements apply to all personnel, SLAC and subcontractor, engaging in excavation operations, including trenching, at SLAC (see Definitions). Penetrations and tunneling operations are not within the scope of this chapter.

For requirements regarding penetrations, see Chapter 44, "Penetration Safety". For requirements regarding tunneling/underground construction, including cut-and-cover excavations that are both physically connected to on-going underground construction operations, and covered in such a manner as to create conditions characteristic of underground construction, see 29 CFR 1926.800).

Exemptions

Hand Work

The following types of excavations are not subject to the requirements of obtaining an excavation permit or having an excavation competent person at the location of the work as described in this chapter:

1. Soil sampling with hand tools such as a trowel, hand auger, or maul that does not exceed a depth of one foot
2. Soil, concrete, and asphalt sampling from bins, hoppers or stockpiled soil with hand tools
3. Gardening and landscaping with hand tools (such as shovel, rake, and hoe) in established planting areas or the SLAC Garden Area not exceeding one foot in depth.

Use of a slide hammer, mattock, post-hole digger, roto-tiller, or pick are subject to the requirements of this chapter, as well as any hand work projects in which utilities or any hazardous conditions are likely to be encountered while hand digging.

Emergencies

If an emergency excavation is necessary, that is if an immediate danger to life, health, the environment, or SLAC facilities exists if an excavation is not performed, an emergency excavation may begin, but only under the direct supervision of an excavation competent person. As soon as practical, an excavation permit must be completed for the emergency excavation (see Requirements).