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.
During the MOL’s excavation safety blitz, inspectors will be targeting the following types of excavation projects:
- “trenching” (digging of long narrow excavations) to install or repair services such as natural gas, electrical, telecommunications, and sewers
- construction of foundations
- “soil retention” (stabilizing soil in an excavation)
- digging basements for residential housing
- forming “footing” (supports) for the construction of buildings or bridges
- road construction and repair involving excavation.
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
- 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:
- trench boxes