Excavation work and trenching are considered to be highly hazardous operations in the construction industry. Precautions must be taken to ensure the safety of all personnel working in this environment.
What is a Trench?
An excavation is any man-made excavation of the soil. It includes trenches as well as cavities made by earth removal. A trench is an underground excavation, generally deeper than it is wide. A trench is usually no wider than 4.5 metres.
What are the Hazards?
The greatest hazard imposed by trench work is that the trench or excavation might collapse and cause injury or even death to a worker. Other hazards include the operation of heavy machinery to build trenches, the proximity of machinery traffic, any electrical wiring overhead or underground, handling of materials in the trench environment and underground utilities like natural gas. Other hazards include falls or falling loads.
The greatest risk in working in trenches is that they will cave in. Cave-ins are considered more likely to occur than any other excavation related accident. Cave-ins are potentially life threatening, so where possible trench shields should be used. Trench Shields can be used to help protect workers performing their roles within a trench. A trench shield is generally constructed of steel or aluminium and features sidewalls that are held apart by spreaders. The spreaders will vary in size depending on the width of the trench.
If a trench is deeper than 1.5 metres protective systems are required unless the trench is dug in stable rock. Deep trenches will require a protective system to be designed by an engineer to ensure safety standards are met.
A number of protective systems can be employed. Sloping is a system that requires the trench wall to be cut back at an angle away from the trench. This minimises the risk of a cave-in. Shoring an also be installed to prevent potential cave-ins. Trench shields also help to support soil and prevent cave-ins from occurring. Engineers will assess factors such as soil type, depth of trench, water content of the soil, weather and loading to devise the most appropriate protective system.
Trenches need to be inspected regularly, usually daily, as conditions can change quickly. A highly competent worker with a sound knowledge of excavation safety should be employed for this task. This person will need to locate and eliminate potential hazards.
All access points to trenches and excavations needs to be thoroughly monitored for safety. This includes steps and ramps down into a trench as well as ladders used to exit trenches. Entry and exit points need to be located nearby all workers.
Common sense should prevail. Heavy equipment must be kept away from the edge of trenches in order to avoid compromising edges. Trenches should be inspected at the start of each shift. Trenches should be inspected following any bad weather event, particularly a rain storm. Tests should be carried out to determine oxygen levels and also the presence of hazardous fumes or toxic gases.