Safe Use of Trench Boxes

Trenching & Excavation Safety
English (NZ)

The Problem

Excavation work is one of the most hazardous activities on any construction site. Cave-ins are sudden, unpredictable, and deadly—just one cubic metre of soil can weigh as much as a car. Trench boxes are designed to protect workers, but if they’re used incorrectly, they can give a false sense of security and still leave you at serious risk. Today, we’ll cover how to use trench boxes safely and effectively to protect yourself and your team.

Identify the Hazards

  • Cave-Ins: Can occur if the trench box is incorrectly installed, positioned, or if workers operate outside its protection.

  • Unsafe Entry and Exit: Using inappropriate methods, such as climbing spreader bars or side walls, increases fall and crush injury risk.

  • Unprotected Areas: Leaving the safety of the trench box, even briefly, exposes you to immediate risk of soil collapse
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  • Damage to Trench Boxes: Using trench boxes that are bent, cracked, or missing components compromises protection and may result in structural failure.

Safety Practices and Preventative Measures

Entry into the Trench Box

  • Wait until the Competent Person has inspected and cleared the trench box before entering.
  • The Competent Person ensures the box is properly installed and structurally safe to use.

Safe Work Practices During Installation and Removal

  • Always exit the trench or move to a safe area while the trench box is being installed, removed, or repositioned.
  • Never stand under, inside, or adjacent to the trench box during vertical movement—soil shifts can occur suddenly.

Avoiding Unprotected Areas

  • Do not step outside the trench box—not even for a moment.
  • Cave-ins happen without warning and can be fatal. Stay within the shielded area at all times.

Safe Methods of Entry and Exit

  • Use a secured ladder or approved access method when entering or exiting the trench box.
  • The ladder must:

    • Extend at least 1 metre above the landing surface.
    • Be placed inside the trench box or another protected zone.
    • Be stable and secure against displacement.
  • Never climb spreader pipes, walls, or bracing.

Inspecting Trench Boxes

Before use, check for:

  • Missing components
  • Bent or broken spreader pipes
  • Damaged welds or missing retainer pins
     If any damage is found, report it to the Competent Person immediately. Do not use a damaged trench box.

Proper Positioning of Trench Boxes

  • The top of the trench box should sit at or above ground level.
  • If the box settles or drops below the surface, stop work and report it immediately.

Excavating Below the Trench Box

  • Excavation of up to 600 mm below the trench box may be allowed only under strict conditions.
  • Always consult the Competent Person before doing s

Real-Life Case or Scenario

Where possible, use an actual incident that you have experienced or been involved in.

Recently, a worker left the trench box to retrieve a tool just outside the protected area. Moments later, the trench wall collapsed, burying the worker up to his waist. While the worker survived, he suffered serious injuries and required rescue. This incident could have been avoided by staying within the protection of the trench box.

Employee Responsibilities

  • Do not enter a trench box unless it’s been inspected and approved by the Competent Person.

  • Use proper ladders for entry and exit—never climb trench box components.

  • Report damaged trench boxes before use.
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  • Stay inside the protected area at all times.

Employer Responsibilities

  • Provide inspected and well-maintained trench boxes for use.

  • Train all workers on safe trench practices and WorkSafe NZ excavation requirements.
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  • Assign a Competent Person to oversee trench box safety and respond to any issues.

Discussion & Questions

  • “What issues have you encountered when working with trench boxes?”
  • “Has anyone experienced a near-miss or cave-in while working near trenches?”
  • “What habits help you remember to stay inside the protective zone?”

Encourage open discussion and sharing of concerns or experiences.

Commitment/Action Plan

Starting today, let’s commit to: Staying within trench boxes at all times, Using approved ladders for access, Reporting damage or unsafe practices immediately. If you’re ever unsure or notice something isn’t right, speak up—your safety is worth it.

Wrap-Up

Trench boxes are designed to save lives—but only if they’re used correctly. By following best practices, working together, and watching out for one another, we can stay protected and avoid injury or worse. Thanks for keeping safety front of mind.

Standards Overview

Under the Health and Safety at Work Act 2015 (HSWA) and WorkSafe NZ excavation safety guidance, employers must:

  • Provide protective systems, such as trench boxes, for excavations deeper than 1.5 metres.

  • Ensure trench boxes are properly installed, inspected, and used under the supervision of a Competent Person.

  • Ensure access/egress is safe and provided every 7.5 metres for workers in trenches over 1.5 metres deep.

  • Prohibit work in damaged trench boxes until repairs are made.

Refer to WorkSafe NZ’s Excavation Safety Good Practice Guidelines for more information.

Disclaimer

These toolbox talks are provided for informational and educational purposes only and are not a substitute for professional legal, health and safety, or regulatory advice.

The content reflects recognised best practices and general industry standards as at the date of publication. However, it may not be applicable to all workplace environments or specific operational contexts.

It is the responsibility of the Person Conducting a Business or Undertaking (PCBU), as well as officers, workers, and other duty holders under the Health and Safety at Work Act 2015 (HSWA), to ensure compliance with all relevant laws, regulations, and WorkSafe New Zealand guidance.

The authors, presenters, and distributors of this toolbox talk disclaim all liability for any loss, damage, or injury arising from the use or reliance on the information provided. Users should seek advice from a suitably qualified health and safety professional or legal advisor for guidance tailored to their specific circumstances.

Always follow your organisation’s policies, procedures, and safe work practices to manage risks and maintain a safe and healthy workplace.

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Last Updated:
May 12, 2025