Excavations and Trenches

An excavation is any man-made cut, cavity, trench or depression in the ground, formed by the removal of earth.

A trench is an excavation that is deeper than it is wide.

Without proper controls, working in or around any excavation poses many risks such as cave-ins, being struck by moving machinery, slips, falls and exposure to hazardous substances.

Because a significant number of deaths and injuries in sewer and underground utility work are directly related to trenching, it is important to know how to work safely in and around trenches.

As an employer you must:

BEFORE you dig:

• Ensure underground utilities are located and marked. [Reg. 91-191, S.180(1)]
• If the work is within 600 mm of underground utilities, inform the authority of the underground utilities before digging. [Reg. 91-191, S.180(2)(a)]
• Ensure that the utilities are properly de-energized before starting the work. [Reg. 91-191, S.180(2)(b)]
• Ensure employees follow safe operating procedures.[Reg. 91-191, S.180(2)(c)]
• Instruct supervisors and employees on the requirements of the regulations and ensure they comply.

As the work progresses:

• Ensure that the walls of an excavation or trench are supported by shoring, bracing or caging unless: [Reg. 91-191, S. 181(1)]
  • It is less than 1.2 m deep
  • It is sloped or benched to within 1.2 m of the bottom with the slope or bench not exceeding 1 m of rise for each 1 m of run
  • No employees are required to enter the excavation or trench, or
  • It is cut into rock that is solid and stable.
    • If not stable, walls and crests must be adequately supported by rock bolts, wire mesh, shoring or another equivalent method. [Reg 91-191, S. 181(2)]
• When powered mobile equipment or mobile cranes are used near the edge, any shoring, bracing or caging is adequate to support the increased pressure. [Reg. 91-191, S. 181(3)]
• Ensure that shoring, bracing or caging is certified by an engineer and be prepared to provide proof of the certification to an officer on request. [Reg. 91-191, S. 181(4)]
• Ensure employees do not enter a trench more than 1.2 m deep unless it is properly supported by shoring, bracing, or caging, or is sloped or benched. [Reg. 91-191, S.182(1)(a)]
• Ensure a ladder extends 1 m above the trench and is no more than 15 m away from the employees or other safe means of access and egress is provided. [Reg. 91-191, S.182(1)(d)]
• Employees may enter an excavation 1.2 m or more in depth to install bracing as long as they remain a distance from the face equal to or greater than the depth of the excavation. [Reg. 91-191, S.182(2)]
• Ensure employees do not enter the excavation or trench to install or remove the shoring or caging. [Reg. 91-191, S.182(3)]
• Ensure that excavated material is kept at least 1.2 m away from the edge of an excavation or trench. [Reg. 91-191, S.183(1)]
• Ensure the excavation or trench is kept reasonably free of water. [Reg. 91-191, S.184(1)]
• Ensure that air testing is carried out in trenches with hazardous atmospheres before any employee enters the trench. [Reg. 91-191, S.184(2)]
• Ensure there is an employee working on the surface who is able to observe those employees working in the trench. [Reg. 91-191, S.185]
• Follow the specific steps when using powered mobile equipment and cranes near excavations and trenches. [Reg. 91-191, S.186...187)]
• Provide adequate illumination when work is carried out in or near an excavation or trench. [Reg. 91-191, S.188(1)(a)]
• Provide warning lights or reflective materials and an adequate barrier around the area to prevent accidental entry. [Reg. 91-191, S.188(1)(b) and S.188(2)]
• Ensure trenches and temporary protective structures are inspected for potential hazards and defects.

While the employer is ultimately responsible for all the provisions mentioned above, the supervisor has a vital role to play in the safety of their teams. As a supervisor, you must:

• Acquaint your employees with the hazards and control measures associated with their work
• Provide the information and instruction necessary to ensure their health and safety
• Enforce company safety rules, programs, codes of practice and procedures, including ensuring employees comply with the requirements below.

As an employee you must:

• Follow safe work procedures established by your employer.
• Not work inside trenches if they are not adequately protected from cave-ins and other risks. [Reg. 91-191, S.182(1)(a)]
• Wear all personal protective equipment provided by the employer, such as hard hats, safety boots and safety glasses.
• Conduct daily checks on temporary structures for possible defects.
• Be aware of all potential health and safety hazards/risks and the controls put in place to prevent them.
• Watch out for hazards in excavations including soil conditions.
• Report promptly to the employer or supervisor any hazardous situations of equipment and work site.

Inspections

Sloping, shoring and trench boxes should be checked regularly.

Hydraulic Shoring

With hydraulic shoring, look for:

• Leaks in hoses and cylinders
• Bent bases
• Broken or cracked nipples
• Cracked, split, or broken sheathing

Report any of these conditions to your employer or supervisor.

All shoring and bracing must be certified by an engineer.

After installation, inspect wales for signs of crushing. Crushing indicates structural problems and the need for more struts.

Always check areas near shoring where water may have seeped in. The combination of water and granular soil can lead to washout. This undermines the trench wall and has killed and injured employees on several occasions.

Timber Shoring

Check timber shoring before it’s installed. Discard any damaged or defective lumber.

With timber shoring, check for:

• Cracked or bowed sheathing
• Wales crushed where they join struts
• Loose or missing cleats
• Split or bowed wales
• Struts off-level

During use, check the box regularly and often to make sure that it is not shifting or settling more on one side than the other.

This can indicate the movement of soil or water underneath.

If the box is shifting or settling, get out and tell your employer or supervisor about it.

Trench Boxes

Inspect trench boxes for damage, cracks in welds, and other defects.

In trench boxes, look for:

• Deformed plates
• Bent or distorted welds in sleeves and struts
• Missing struts
• Bent struts
• Holes, bends, or other damage to plates

Ground around trenches

The ground around trenches should be inspected for tension cracks. These may develop parallel to the trench at a distance of about one-half to three-quarters of the trench depth.

If you find cracks in the ground, alert the crew and double-check your shoring or trench box.

It’s dangerous to overlook damage or defects in protective systems.