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:
As the work progresses:
As an employee you must:
With hydraulic shoring, look for:
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.
Check timber shoring before it’s installed. Discard any damaged or defective lumber.
With timber shoring, check for:
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.
Inspect trench boxes for damage, cracks in welds, and other defects.
In trench boxes, look for:
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
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.
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]
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.
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.
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.
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]
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.