Trenching & Excavation

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Trenching and excavating are common construction activities and and if not performed safely, can result in serious injuries and even fatalities.  An excavation is any kind of  cut, cavity, trench or depression in the earth’s surface resulting from rock or soil removal.

A trench is a very specific type of excavation, specifically one that is:

  • less than 3.7 metres [12ft] wide at the bottom;
  • more than 1.2 metres [4ft] deep; and
  • any length.

Hazards

The most common types of hazards that cause fatalities during trenching and excavating are:

Cave-ins
Power line contacts

The risk of cave-in or coming into contact with an energized power line are not the only hazards when working in or near a trench. Many other injuries and deaths are also related to:

Vehicular traffic

Dropped objects

Exposure to toxic, irritating or flammable gasses

Struck by heavy equipment

Falling over unprotected edges

Material handling

Uneven ground

Common Controls

All of the above hazards can be controlled to either eliminate or minimize the risk to an acceptable level. Some of these control measures include:

Sloping involves cutting the walls of a trench back at an incline, away from the work area.  The angle of incline depends on the type of soil that is being excavated.

Shoring is a way of bracing the walls of a trench to prevent collapse.  Shoring typically involves the use of panels (wood, aluminum etc.) that are positioned against the walls of the trench and held in place using posts, screw jacks or other effective means. Shoring systems must be capable of withstanding the forces that could be placed upon it.

A trench box is a steel or aluminum structure that is placed inside of a trench to protect workers.  As long as workers remain inside the trench box, workers inside are protected in the event of a trench wall collapse.  When selecting a trench box, the width and height of the trench must be considered along with the potential load that could be applied to its walls.

  • Sheet piling consists of a series of interlocking panels (or sheets) that are driven into the ground, to create reinforced walls for a trench, prior to excavating.

Safe means to enter/exit the trench/excavation should be provided to workers and not impede their exit.

Hazard specific Personal Protective Equipment (PPE) should be work by workers at all times. This could include high visibility clothing/vest, hard hats, safety gloves & footwear, respiratory protection, protective eye wear (glasses/googles), hearing protection etc.

Ensure that there is a process to ensure the regular inspection of all tools and equipment, including protective structures (i.e. trench box, shoring etc.).  Ensure that trenches/excavations are regular inspected for signs of compromise, particularly after changes in weather or time away from site.

Prior to digging, a company must ensure that all underground utilities are identified and marked.

Ensure that all tools and equipment are kept away from the edge of the trench.  It is useful to identify a safe lay down area to ensure that nothing is inadvertently dropped into the trench where workers could be working.

Prior to the commencement of work, an emergency response plan must be developed and communicated to all workers. This will include:

  • Emergency response procedures
  • A means to communicate with emergency responders
  • Emergency medical care and materials that will be available to treat injured entrants on site.

Where the movement of traffic poses a risk to workers in an area, an effective means of traffic control would be required.

Any person operating equipment that has the potential to encroach on a power line, is required to be in possession of current Power Line Hazard Training certification, as prescribed by the NL OHS Regulations.

Training Requirements

Workers should receive instruction on the hazards associated with trenching and excavation, controls necessary and emergency response.  Participants in the COR® Program must ensure that those involved in trenching activities complete a formal trenching and excavation training course that has been reviewed and approved by the NLCSA.

To ensure the safety of workers in and around a trench or excavation, training appropriate to the hazard will be required. This might include certification in Traffic Control, Power Line Hazards, Confined Space Entry, WHMIS 2015 etc.

In addition to the legislative training, workers must receive training on the specific equipment that they may be required to use and task specific procedures.

NLCSA Trenching Resources

TitleContentCategoriesFile TypeLink
Trenching & Excavating ProcedureSafe Job ProcedureSafe Job Proceduresdocx
Download
Mounting & Dismounting ExcavatorsToolbox TalkMobile Equipmentpdf
Download
Trenching and Excavation SafetyToolbox TalkGeneralpdf
Download
Trenching & Excavation Work – High Risk Activity Infosheetpdf
Download

External Resources

NL Occupational Health and Safety Explanation Guide – Trenching  Excavating