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Trenching & Excavation

An excavation is a hole left in the ground as the result of removing material. A trench is an excavation in which the depth exceeds the width. Trenching and excavation work is inherently dangerous. Hazards include cave-ins, struck-by injuries, electrical contact, and slips, trips, and falls.

As part of Safe At Work Ontario's strategy to raise awareness of the hazards involved in this type of work, to prevent injuries and illnesses that could arise from unsafe work practices, and to ensure workplace parties are complying with health and safety legislation, the Ministry of Labour (MOL) will be conducting a safety blitz on excavation projects in July and August of 2015.

 

Hazards

Cave-ins

One of the biggest hazards related to trenching and excavation is the risk of cave-ins. An unstable trench or excavation can collapse, killing or injuring workers by suffocation or crushing when a worker is buried by falling soil. Trench stability is affected by a number of factors such as:

  • improper use or installation of support system or trench box
  • soil type and moisture content
  • weather
  • vibration
  • depth of the trench
  • length of time the trench is left open
  • surcharge (excessive weight near the trench)
  • adjacent buildings and structures
  • existing foundations, and
  • previous excavations or soil disturbances.
 

There are three basic methods of protecting workers against trench cave-ins:

  • sloping
  • shoring
  • trench boxes
 

Most fatal cave-ins occur on small jobs of short duration such as service connections and excavations for drains and wells. Too often people think that these jobs are not hazardous enough to require safeguards against collapse. Unless the walls are solid rock, never enter a trench deeper than 1.2 metres (4 feet) if it is not properly sloped, shored, or protected by a trench box.

 

Other Hazards

The risk of a cave-in is not the only hazard in trenching. Injuries and deaths are also related to other major areas:

  • falls into excavation or trench
  • slips, trips, and falls while accessing, egressing, or working in the excavation or trench
  • insufficient personal protective equipment
  • contact with overhead electrical conductors and underground utilities
  • materials handling and housekeeping
  • heavy equipment working near the excavation
  • traffic control on the site and on public roads
  • confined spaces and hazardous atmospheres
  • material, equipment, or vehicles falling onto workers in excavations or trenches
  • excavation or trench affecting stability of adjacent structures
  • storage of excavated material
  • voids, underground parking garages, vaults, subways
  • flooding/water hazards.
 

IHSA Resources

Before excavating, the gas, electrical, and other services in the area must be accurately located and marked. If the service poses a hazard, it must be shut off and disconnected. Over half of all powerline contacts involve buried cable.

For more info, download the Trenching Hazards chapter of our Construction Health and Safety Manual.

 

Regulations

Part III (sections 222 to 242) of the Construction Regulation applies to all excavating and trenching operations. It identifies the various types of soils and specifies the type of shoring and timbering to be used for each. It spells out the precautions that must be taken before an excavation is begun and the requirements for trench support systems that must be designed by a professional engineer.

 

Training

 

Products

 

Safety Talks

Conducting a five-minute safety talk is hands-on way to remind workers that health and safety are important on the job and can help workers recognize and control hazards.

 

Articles

 

MOL Resources

Visit the MOL website for more info about the blitz.

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