Toolbox Talk: Are Trench Excavations Confined Spaces?

Understanding Confined Spaces

According to OSHA, a confined space is defined as:

• Size and Configuration: Large enough for an employee to enter and perform work.
• Limited Entry and Exit: Has restricted means for entry or exit.
• Not Designed for Continuous Occupancy: The space is not intended for continuous employee occupancy.

Given this definition, a trench excavation can indeed meet the criteria for a confined space.

Defining Trench Excavations

OSHA defines a trench excavation as:

• Narrow Excavation: A narrow space dug below the ground’s surface.
• Depth vs. Width: Generally, the depth is greater than the width.
• Width Limit: The width at the bottom of the trench is typically no greater than 15 feet.

Permit-Required Confined Spaces and Trenches

A permit-required confined space has additional characteristics that can also apply to trench excavations:

1. Hazardous Atmosphere:
   1. Trenches can develop hazardous atmospheres, such as oxygen deficiency or the presence of toxic or flammable gases like carbon monoxide, methane, and hydrogen sulfide. These conditions are especially likely near combustion engines, sewage lines, landfills, swamps, and other potential sources of dangerous gases.
   2. OSHA mandates that if a hazardous atmosphere is reasonably expected, the trench must be tested before any workers enter, especially if the trench is over 4 feet deep.
2. Engulfment Hazards:
   1. Trenches pose a risk of engulfment from collapsing walls or materials, especially if the trench lacks adequate sloping or shoring. Excessive water from rain, groundwater, or leaking pipes can also increase the risk of engulfment.
3. Trapping or Asphyxiation Risks:
   1. Trenches can have configurations that could trap or asphyxiate a worker, particularly if the walls converge inward or if the floor slopes downward, tapering to a narrower section.
4. Other Safety and Health Hazards:
   1. Accessing a trench deeper than 4 feet often requires a ladder, which introduces the risk of slips and falls. Additionally, workers in trenches are at risk of being struck by excavation machinery or falling debris from above.

Summary

Trench excavations can indeed present many of the hazards associated with permit-required confined spaces. Any trench over 4 feet deep should be treated as a confined space until a competent person has assessed and ruled out all potential hazards. It’s essential to recognize the risks involved in trench work and ensure that all necessary precautions are taken to protect workers from hazardous atmospheres, engulfment, entrapment, and other safety threats.