Photo of an excavation site with a Danger Due To poster on a fence

Trenching and excavation work can be dangerous if proper procedures are not followed. Hazards include cave-ins, struck-by injuries, electrical contact, and slips, trips, and falls.

The Excavations section (Part III, s. 222 to 242) of the Construction Projects regulation (213/91) 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.

It is important to understand the difference between the terms trench and 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.




One of the biggest hazards related to trenching is the risk of cave-ins. An unstable trench 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 boxes
  • soil type and moisture content
  • weather
  • vibration
  • depth of the excavation
  • length of time the excavation is left open
  • surcharge (excessive weight near the excavation)
  • adjacent buildings and structures
  • existing foundations, and
  • previous excavations or soil disturbances.

There are three basic methods of protecting workers against excavation 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:


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.

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






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.




External Resources