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Publication: September 2008. For information about changes, please see the Revision History.

Chapter 11: Excavation Safety

Overview (1)

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 Section 4, “Definitions”.)  This chapter sets forth requirements for all trenches and excavations.

The requirements of this chapter are based on the best available management practices in excavation safety. These requirements will reduce the risk of a subsurface strike to the lowest practical level.

Hazards/Impacts (1.1)

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

• 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 the following.

• 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 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 (2)

The excavation safety program and its requirements apply to all personnel, SLAC and subcontractors, engaging in excavation operations (see Section 4, “Definitions”) at SLAC that meet any of the following conditions, at any time:

1. Are one foot or more in depth
2. Involve the use of power tools
3. In which utilities are identified or any hazardous conditions are likely to be encountered

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 ongoing underground construction operations and covered in such a manner as to create conditions characteristic of underground construction) see 29 CFR 1926.800.

Note: Requirements from other chapters may still apply to excavations not covered by this chapter. For example, all excavation operations need to meet the requirements of Chapter 17, "Hazardous Waste". In particular, soils may need to be classified for potential hazards and disposition. See Section 7, "References”, for a list of chapters with requirements related to excavations.

Exemptions (2.1)

The following types of excavations are exempted from the requirements of this chapter, even if they meet the conditions above:

1. Soil, concrete, and asphalt sampling from bins, hoppers, or stockpiles, using hand tools
2. Replacement of existing sign posts in and around SLAC roads, parking areas, and pathways, provided sleeves are utilized

Emergencies (2.2)

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. (See Section 4, “Definitions”.) As soon as practical, an excavation permit must be completed for the emergency excavation (see Section 5, “Requirements”).

Implementation (8)

The requirements of this chapter will be implemented according to Excavation Safety: Implementation Plan [pdf].

continue to Standards (3)