Trenching operations present several hazards that require careful risk assessment and control measures. Here's a breakdown of potential hazards and mitigation strategies:

Hazards:

• Cave-ins: The primary hazard in trenching is cave-ins, which can entrap, bury, or injure workers . This risk is especially high in trenches deeper than 1.2 meters (approximately 4 feet) 2, 4.
• Falling Loads: Materials or equipment falling into the trench can cause serious injuries. Ensure equipment and spoil piles are at least 1 meter away from the trench edge .
• Hazardous Atmospheres: Trenches can accumulate hazardous gases or become oxygen-deficient 1, 6, 17. This is especially a concern in confined spaces or areas with potential gas leaks.
• Water Accumulation: Accumulated water in a trench can lead to instability and increase the risk of collapse, as well as posing drowning hazards 6, 20.
• Underground Utilities: Contacting underground utilities (gas, electric, water, sewer) during excavation can result in electrocution, explosions, or flooding .
• Adjacent Structures: Excavation work can compromise the stability of nearby buildings or structures 6, 9.
• Equipment Hazards: Powered mobile equipment used near the trench edge can cause cave-ins or accidentally fall into the excavation 9, 12.
• Access and Egress: Inadequate or unsafe access and egress can lead to falls or delays in emergency situations 9, 11.

Risk Assessment:

• Likelihood: Assess the probability of each hazard occurring based on soil type, weather conditions, proximity to utilities, and equipment usage.
• Severity: Evaluate the potential consequences of each hazard, considering the potential for serious injury, fatality, or property damage.

Control Measures:

1. Elimination/Substitution:
   • Consider alternative methods to trenching if possible.
2. Engineering Controls:
   • Sloping/Benching: Slope the trench walls at a safe angle based on soil type. Type 1 and 2 soil should be sloped to 45 degrees within 1.2 meters of the bottom of the trench . Sloping must be to within 1.5 meters for 'hard and compact soil' and 'likely to crack or crumble soil' .
   • Shoring: Install shoring systems (e.g., timber, aluminum hydraulic) to support trench walls 1, 2, 3. Ensure shoring is adequately designed and installed 2, 4.
   • Shielding: Use trench boxes or shields to protect workers from cave-ins .
   • Water Removal: Implement water removal techniques to prevent water accumulation 6, 11, 20.
   • Barriers: Install barriers around the excavation to prevent accidental entry of vehicles or personnel 7, 8, 19.
3. Administrative Controls:
   • Competent Person: Designate a competent person to inspect the trench daily for hazards 3, 6.
   • Underground Utility Location: Locate and mark all underground utilities before excavation 8, 13, 15. Use safe digging practices near utilities .
   • Emergency Procedures: Develop and communicate emergency rescue procedures .
   • Training: Provide comprehensive training to all workers on trenching hazards and safe work practices .
   • Shoring Installation/Removal: Install shoring from the top down and remove it from the bottom up, using a ladder .
4. Personal Protective Equipment (PPE):
   • Hard Hats: Required for all personnel in the vicinity of the trench.
   • Safety Glasses: To protect against flying debris.
   • High-Visibility Clothing: To ensure workers are visible to equipment operators.
   • Harness and Lifeline: When entering deep or confined excavations .

Monitoring and Review:

• Regularly inspect the trench for any signs of instability, water accumulation, or hazardous atmospheres.
• Review the risk assessment and control measures whenever there are changes in site conditions, equipment, or personnel.

Specific Recommendations:

• For trenches deeper than 3 meters, have a professional engineer design and certify the protective system 2, 14.
• Ensure a competent worker is stationed on the surface to monitor conditions and provide emergency assistance for trenches deeper than 1.2 meters .
• Never allow workers to enter a trench that is not adequately protected.
• Keep all drawings and instructions for temporary protective structures at the excavation site .
• Ensure that shoring components are securely connected to prevent failure .
• Prohibit workers from working under lowered materials .
• Provide adequate illumination to prevent inadvertent entry and ensure safe working conditions .