Excavation & Trenching
Safety Tips for
Using Trench Boxes
Using Trench Boxes
OSHA 1926.652(c) · Trench Box Must Match Soil Conditions · Proper Installation Required
A trench box (shield) is the most commonly used method of excavation protection on NYC construction sites — it is faster to set up than shoring and doesn't require timber calculations. But a trench box is only as safe as it is correctly installed and matched to the soil conditions. A box that moves, tips, or is installed at the wrong depth provides no protection when the soil fails.
Correct Trench Box Installation
- The box must be installed so that workers are always within the shielded area during work — no working outside the box in unprotected soil
- Excavation can extend 2 feet below the bottom of the shields, but workers must not enter below the shield in Type C or wet soil
- The top of the shield must extend above the highest point of excavation unless otherwise designed by a PE
- Boxes must be positioned so they cannot move during use — wedged against the trench wall or pinned to prevent racking
- Never stack shields on top of each other unless specifically rated for stacking by the manufacturer
Moving the Box
- Workers must be out of the trench before the box is moved — the excavation is most unstable during repositioning
- The crane or excavator moving the box must not exert horizontal force against the soil — move the box vertically, repositioning one end at a time
- Inspect the exposed trench wall for cracks, sloughing, or moisture changes after each box movement — conditions change as the excavation progresses
NYC Sites — What Trench Boxes Don't Protect Against
- A trench box does not prevent soil from caving in above the box — it only protects the worker inside the box if the soil does fall. The box is not a substitute for proper soil classification
- Adjacent building foundations can fail if unprotected excavations undercut their footings — a PE must review any excavation within the influence zone of existing buildings
- Box manufacturer's documentation must be on site — the rated capacity, allowable depth, and stacking restrictions are equipment-specific
Discussion Questions
- You need to reposition the trench box to advance down the line. What must happen before it moves?
- Can workers be inside the trench box while the excavator moves it? Why or why not?
- A coworker says they can work 4 feet below the bottom of the shield because "the box is right there." Is this acceptable?
- What documentation for the trench box must be available on this site?
Sign-Off
Project Address
Date
Time
Foreman / Supervisor
SSM / SSC Name & License No.
Worker Attendance
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