Excavations - hazards and control

There are about seven deaths each year due to work in excavations and these are often related to the composition and structure of the soil which forms the walls of the excavation. Many types of soil, such as clays, are self-supporting but others, such as sands and gravel, are not. The walls of excavations can collapse without any warning resulting in death or serious injury. Many such accidents occur in shallow workings. It is important to note that, although most of these accidents affect workers, members of the public can also be injured. 

The specific hazards associated with excavations are as follows  

The build-up of fumes can be particularly hazardous since it may lead to asphyxiation, fire or explosion. When 

If the excavation work takes place below the local groundwater level or water table, then water will flow into the trench. Measures will be required to impede the inflow of water and channel the water in the trench to a sump or pond where it may be pumped to a safe discharge point. These problems will be exacerbated at times of high rainfall, such as late winter or early spring and will be even more hazardous if the soil structure is naturally weak. 

Instability may also be caused by additional loading in the area adjacent to the excavation, for example by vehicles, plant or a spoil tip. This is known as surcharging. Possible actions to reduce this risk are given in 9.2.4. 

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