Dangers of excavations

Lesson Progress:

The sides of a trench may look firm, but looks can be misleading. Excavations and trenches collapse for the following reasons.

  • The sides are not supported or supports are not installed properly.
  • Vehicles operate too close to the edge (for example dumpers, excavators or other large vehicles).
  • Materials and spoil are stored too close to the edge.
  • The ground dries out, shrinks and collapses.
  • Heavy rain weakens the ground and the sides. Groundwater in an excavation also weakens the sides.
  • The excavation is too close and undermines or weakens nearby walls and structures, causing them to collapse.
Keep vehicles a safe distance away from the edge of an excavation. A truck carrying 6m3 of concrete weighs approximately 26 tonnes.
Possible dangers of trenches

There are many dangers when working within excavations. To work safely the following hazards may need to be considered.

  • Falls of materials, people, plant and vehicles into the excavation.
  • Making foundations of nearby structures weak, including scaffolds and other temporary works structures.
  • Accidental or deliberate contact with underground services.
  • Water or other fluids entering the trench, standing water and pumping out.
  • The presence of naturally occurring gases (such as hydrogen sulphide (H2S)).
  • The build-up of gases that are heavier than air (such as H2S and liquefied petroleum gas (LPG)).