Excavation Safety – Cave-In Protection and Requirements
The Problem
Excavation work is one of the most dangerous tasks on any construction site. 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 over 1,200 kilograms—about the same as a small car. If you're caught in a collapse, that weight can crush you, cause suffocation, or result in permanent injuries. These incidents are entirely preventable. Today, we’ll focus on cave-in hazards, the types of protective systems available, and the critical role the Co
Identify the Hazards
Weight of Soil
- One cubic metre of soil weighs over 1,200 kg.
- Even a small amount of falling soil can cause serious injury or death.
Injury Risks
- Potential injuries include:
- Broken bones
- Internal injuries
- Muscle damage
- Suffocation from being trapped
- Once buried, it's nearly impossible to breathe or escape without rescue.
Soil Stability Risks
- Collapse triggers can include:
- Unstable soil conditions
- Water infiltration
- Nearby heavy equipment
- Ground vibrations
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 trench walls to relieve pressure and improve stability.
Shoring Systems
- Use engineered supports, such as timber or hydraulic shoring, to stabilise trench walls and prevent collapse.
Trench Shields/Boxes
- Prefabricated trench boxes protect workers from soil collapse during excavation activities.
Note: Only a Competent Person can determine which protective system is appropriate. This decision is based on:
- Soil type
- Excavation depth
- Site-specific conditions
- WorkSafe NZ Excavation Safety Guidelines
Real-Life Case or Scenario
A labourer on a Mississauga job site was using a grinder without eye protection, thinking it would only take a second. A metal shard flew into his eye, causing a serious injury and time off work. The incident could have been prevented if proper PPE had been worn, as required by CCOHS guidelines.
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—such as sloping, shoring, or trench boxes.
- Provide training on excavation hazards, CCOHS guidelines, 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—these 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 in place and by following the guidance of the competent person, we can avoid serious injuries and save lives. Stay alert, follow all site safety procedures, and speak up if you notice anything 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 select the appropriate method of protection.
- Shallower excavations may also require protection if:
- Soil is unstable
- There is water accumulation
- Heavy machinery is operating nearby
- The ground is soft or loose
Disclaimer
“The information provided in this toolbox talk is intended for informational and educational purposes only. It is not a substitute for professional legal, safety, or regulatory advice. The content reflects general best practices and industry standards but may not be applicable to all workplace environments or jurisdictions.
It is the responsibility of employers, supervisors, and workers to ensure compliance with applicable federal, provincial, and territorial laws, regulations, and standards, including but not limited to those set by the Canadian Centre for Occupational Health and Safety (CCOHS) and relevant provincial occupational health and safety authorities. Site App Pro, its affiliates, agents, or representatives—as well as the authors, presenters, and distributors of this toolbox talk—assume no liability for the use or application of the information provided.
Participants are strongly encouraged to consult appropriate legal, safety, or regulatory professionals regarding specific workplace concerns or questions. Always adhere to your organisation’s policies and procedures for health and safety and hazard management.
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