Excavation Safety – Cave-In Protection and Requirements
The Problem
Excavation work is among the most dangerous tasks on any worksite. Cave-ins are the leading cause of fatalities in trenching and excavation. To put it into perspective, a single cubic metre of soil can weigh more than 1,200 kilograms—about the same as a small car. If you’re caught in a collapse, the weight of that soil can crush your body, cause suffocation, or result in permanent injuries. These incidents are completely preventable. Today, we’ll talk about cave-in hazards, protective systems, and the vital role of the Competent Person in keeping everyone safe.
Identify the Hazards
Weight of Soil
- One cubic metre of soil weighs over 1,200 kg.
- Even a small amount of falling soil is enough to cause serious injury or death.
Injury Risks
- Broken bones, internal injuries, muscle damage, and suffocation from being trapped.
- Once buried, it becomes impossible to breathe or escape without rescue.
Soil Stability Risks
- Unstable soil, water infiltration, nearby heavy equipment, or vibrations can trigger collapses.
Safety Practices and Preventative Measures
Sloped Sides
- Slope trench walls away from the excavation to reduce the risk of soil collapse.
Benched Sides
- Create step-like levels in the soil walls to relieve pressure and improve safety.
Shoring Systems
- Use engineered supports like timber or hydraulic shoring to stabilise trench walls.
Trench Shields/Boxes
- Prefabricated trench boxes protect workers from soil collapse during excavation work.
Only a Competent Person can determine which protective system is appropriate—this is based on the soil type, depth, site conditions, and WorkSafe NZ guidance.
Real-Life Case or Scenario
A recent WorkSafe NZ investigation reported a fatal trench collapse where workers were digging in an unprotected trench more than 1.5 metres deep. No Competent Person had been consulted, and there was no protective system in place. The trench caved in without warning, burying one worker beneath a tonne of soil. The incident could have been entirely avoided with proper planning and the use of a trench shield.
Employee Responsibilities
- Never enter an excavation deeper than 1.5 metres without an approved protective system in place.
- Look for signs of unstable soil, water seepage, cracks, or bulging walls.
- Follow all instructions from the Competent Person—do not make assumptions about safety.
- Report unsafe excavation conditions immediately.
Employer Responsibilities
- Assign a Competent Person to assess soil conditions and determine the correct protective system.
- Supply approved safety systems—sloping, shoring, or trench boxes.
- Provide training on excavation hazards, WorkSafe NZ requirements, and emergency procedures.
Discussion & Questions
- “What are some signs that an excavation might be unsafe to enter?”
- “Has anyone seen a trench collapse or experienced unsafe conditions on-site?”
- “Why is it important to have a Competent Person involved before starting excavation work?”
Encourage everyone to participate and share examples—they help build awareness and improve safety culture.
Commitment/Action Plan
Let’s commit today to never entering an unprotected excavation. Always ensure a protective system is in place and consult with the Competent Person before starting work. Safety is everyone’s responsibility—if in doubt, speak up.
Wrap-Up
Trench collapses can happen in seconds—but they’re entirely preventable. With the right protective systems and by following the advice of the Competent Person, we can prevent injuries and save lives. Stay alert, follow site safety procedures, and speak up if you see something unsafe. Your safety is worth more than any job. Thank you for taking it seriously.
Standards Overview
Under the Health and Safety at Work Act 2015 and WorkSafe NZ’s Excavation Safety Good Practice Guidelines:
- Any excavation deeper than 1.5 metres must have a protective system in place.
- A Competent Person must assess soil conditions and choose the correct method of protection.
- Even shallower excavations may require protection if conditions are unstable or if there are additional risk factors (e.g. water, machinery, soft soil).
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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