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.
  • If the work is within 600 mm of underground utilities, inform the authority of the underground utilities before digging.
  • Ensure that the utilities are properly de-energized before starting the work.
  • Ensure employees follow safe operating procedures.
  • 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:
    • 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.
  • When powered mobile equipment or mobile cranes are used near the edge, any shoring, bracing or caging is adequate to support the increased pressure.
  • 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.
  • 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 .
  • 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.
  • 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.
  • Ensure employees do not enter the excavation or trench to install or remove the shoring or caging.
  • Ensure that excavated material is kept at least 1.2 m away from the edge of an excavation or trench.
  • Ensure the excavation or trench is kept reasonably free of water.
  • Ensure that air testing is carried out in trenches with hazardous atmospheres before any employee enters the trench.
  • Ensure there is an employee working on the surface who is able to observe those employees working in the trench.
  • Follow the specific steps when using powered mobile equipment and cranes near excavations and trenches.
  • Provide adequate illumination when work is carried out in or near an excavation or trench.
  • Provide warning lights or reflective materials and an adequate barrier around the area to prevent accidental entry.
  • Ensure trenches and temporary protective structures are inspected for potential hazards and defects.

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.
  • 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 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 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 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.

General Regulation - Occupational Health and Safety Act
N.B. Reg. 91-191

Part XIII EXCAVATIONS AND TRENCHES

Section 180

180. (1) Before beginning an excavation or trench, an employer shall ensure that the location of any underground utility line or piping is determined.

(2) Where employees are working within 600 mm of underground utility line or piping, an employer shall ensure that

(a) the authority operating the utility line or piping has been notified of the operation,

(b) the utility line has been de-energized, and

(c) an adequate operating procedure is used by the employees.

(3) An employer shall ensure that utility poles, posts and similar structures are supported or removed if they are within 3 m of an excavation or trench that is more than 1.2 m deep.

Section 181

181. (1) An employer shall ensure that the walls of an excavation or trench are supported by shoring, bracing or caging except when the excavation or trench

(a) is less than 1.2 m deep,

(b) subject to subsection (2), is cut in solid rock,

(c) is sloped or benched to within 1.2 m of the bottom of the excavation or trench with the slope or bench not exceeding 1 m of vertical rise to each 1 m of horizontal run, or

(d) is one that an employee is not required to enter.

(2) Where the walls or crests of an excavation or trench are cut in solid rock and are not stable, an employer shall ensure that the walls and crests are adequately supported by rock bolts, wire mesh, shoring or a method that provides equivalent support.

(3) Where powered mobile equipment or a mobile crane is used near the edge of an excavation or trench, an employer shall ensure that any shoring, bracing or caging for the excavation or trench is adequate to support the increased pressure.

(4) An employer shall ensure that shoring, bracing or caging for an excavation or trench is certified as adequate by an engineer and shall make the proof of the certification available to an officer on request.

[N.B. Reg. 2001-33, s. 56]

Section 182

182. (1) An employer shall ensure that an employee does not, and no employee shall, enter an excavation or trench 1.2 m or more in depth unless

(a) the walls of the excavation or trench are supported by shoring, bracing or caging, the excavation or trench is cut in solid rock or the excavation or trench is sloped or benched to within 1.2 m of the bottom of the excavation or trench with the slope not exceeding 1 m of vertical rise to each 1 m of horizontal run,

(b) subsections 181(2), (3) and (4) have been complied with,

(c) loose material that may fall into the excavation or trench has been removed, and

(d) a ladder that extends at least 1 m above the excavation or trench is installed no more than 15 m from where the employee is working or some other safe means of access and egress is provided.

(2) Notwithstanding subsection (1), an employee may enter an excavation 1.2 m or more in depth to install bracing if the employee remains a distance from the face of the excavation equal to or greater than the depth of the excavation.

(3) Notwithstanding subsection (1), an employer shall ensure that an employee does not, and no employee shall, enter an excavation or trench 1.2 m or more in depth to install or remove shoring or caging from a position inside an excavation or a trench.

[N.B. Reg. 2001-33, s. 57]

Section 183

183. (1) Subject to subsection (2), an employer shall ensure that excavated material is kept at least 1.2 m away from the edge of an excavation or trench.

(2) Where an excavation or trench is more than 1.8 m deep in rock, an employer shall ensure that

(a) excavated material is located back from the face of the excavation or trench a distance equal to at least the height of the excavated material, or

(b) a fence that is adequate to support the excavated material is erected at a minimum distance of 1 m from the face of the excavation or trench.

Section 184

184. (1) An employer shall ensure that an excavation or trench in which an employee works is kept reasonably free of water.

(2) Where an employee may be exposed to a hazardous gas or to an oxygen deficient or oxygen rich atmosphere in an excavation or trench, an employer shall ensure that testing is carried out in accordance with section 263 before the employee enters the excavation or trench.

(3) An employer shall ensure that no hazardous substance is stored in an excavation or trench.

(4) An employer shall ensure that precautions are taken to prevent the accumulation of hazardous gases in an excavation or trench and that adequate ventilation is provided in the excavation or trench.

Section 185

185. Where an employee is working in an excavation or trench, an employer shall ensure that there is an employee working on the surface who is able to observe the employee working in the excavation or trench.

Section 186

186. An employer shall ensure that an operator of powered mobile equipment or a mobile crane does not lower material into an excavation or trench, and no such operator shall lower material into an excavation or trench, unless

(a) the operator has unrestricted visibility, or

(b) a signaller is used to direct the movement of the material.

[N.B. Reg. 2001-33, s. 58]

Section 188

188. (1) An employer shall ensure that an excavation or trench is adequately illuminated

(a) when work is being carried out in or near the excavation or trench, and

(b) by warning lights or reflective materials to prevent inadvertent entry.

(2) An employer shall ensure that an adequate barrier is set up around the excavation or trench so as to protect employees working in the excavation or trench from vehicular traffic.