Eiffel 101: Overview of OSHA Guidelines for Trenching

In order to keep workers safe, it’s important to understand OSHA’s trench box requirements, including when it’s appropriate to use a trench box and how to use one according to regulation.

Protective systems, including trench boxes, are used when the trench reaches a depth of five feet or more. Protective systems are also required for trenches under five feet deep if the soil is loose and might cave in, particularly in the cases of sand or mud. Before work begins, the conditions of the soil should be evaluated to determine whether a protective system is needed.

Trench Box Overview

A trench box is a system installed to protect workers while they’re digging or excavating the earth. Trench boxes are also known as trench shields, sewer boxes, manhole boxes, or tap boxes. They give a trench stability and allow laborers to work in peace knowing that even if the trench collapses, the pressure and weight of the soil will not trap them.

Trench boxes are not designed to prevent a trench wall from collapsing. Instead, they’re designed to protect workers from the pressure and weight of soil in the event of a cave-in. Unlike a shoring system, a trench box doesn’t provide any structural strength to the excavation itself.

Trench boxes are designed to withstand pressure from the earth surrounding them. Trench boxes are made from aluminum or steel with sidewalls of varying thicknesses held apart by spreaders or other trench box panels. Spreaders are beams that are placed perpendicular to the plates and function as braces. All the components of a trench box are welded together to make the system stable.

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OSHA Installation Guidelines (A Brief Overview)

OSHA outlines proper installation techniques for the use of trench boxes in OSHA 29 CFR Part 1926.650-.652 Subpart P-Excavations. Some of the recommendations are as follows:

  • A contractor should install a trench box in a way that restricts its lateral movement and the space around the box should be backfilled to close any gaps.

  • The maximum distance between the bottom of the trench box and the bottom of the trench should be no more than two feet.

  • Trench boxes can be used alongside other protective systems for increased safety.

  • Trench boxes must be able to handle the pressure at the depth where they’ll be used and for the type of soil they’ll be used in, and these calculations should be verified before installation.

  • For trenches deeper than 20 feet, a registered professional engineer (RPE) must design the trench box, or contractors should select the right trench box for the depth of the excavation using manufacturer’s tabulated data.

  • As trenches get deeper, trench boxes can be stacked on top of one another to provide the necessary protection for workers.

  • Workers should not remain in the trench box when it’s being installed.

  • People working in a trench box must have access to a ladder or other means of escape.

  • OSHA requires employers to train employees on the hazards they may be exposed to when working in a trench box and how to protect themselves in case of emergency.

This blog post is an interpretation of OSHA regulations and standards. Please consult OSHA regulations for comprehensive guidelines.

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