Hazards of Excavation

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.

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.

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, 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.