Hazards of Excavations
The hazards of excavation work include:
Collapse – when the unsupported sides of the excavation slip and cave in. Severe crush injuries can result from even relatively small collapses because the soil is very heavy. Workers buried or entrapped in the soil can asphyxiate in minutes. Workers do not have to be completely buried for asphyxiation to occur; being buried to the chest will lock the rib cage and have the same effect.
Striking buried services – when high-voltage electrical cables, gas pipes, mains pipes or other buried services are struck during the excavation work. This can lead to electric arcing, shock, burns and fire, gas explosion or rapid flooding of the excavation, not to mention the major business disruption to service users.
People falling in – when people fall into the excavation from an unfenced edge or whilst climbing into or out of the excavation from ladders.
Objects falling in – when tools or materials fall from an unprotected edge into the excavation and onto occupants, such as:
–– Vehicles driving close to the side of the excavation.
–– Spoil (loose soil) piled close to the sides of the excavation.
Flooding – from surface water during heavy rain, groundwater or a ruptured water main.
Hazardous substances – in particular, gases and vapors. Considerations include:
–– Excavations will fill with any gas that is heavier than air, such as LPG and carbon dioxide. Adjacent combustion engines (such as generators and compressors) can act as a source of exhaust fumes.
–– The ground surrounding the excavation may contain methane or hydrogen sulfide (both produced by microbial decay) that can leach out of the soil and into the excavation.
–– Excavations might need to be classified as confined spaces for these reasons.
–– Contaminated ground can also present a significant hazard, e.g. the ground may be contaminated with heavy metals.
The collapse of adjacent structures – in digging an excavation, the foundations of nearby buildings may be disturbed, resulting in the destabilizing or collapse of the structure.
Excavation Control Measures
All excavations must be carefully planned. Before digging it is essential to confirm the presence of underground services, and this will include the use of service plans, ground scanning equipment to detect cables and pipes and then establishing a safe method of work. Initially, the work may commence with a trial dig by hand before using heavy plant where appropriate.
- To prevent injury when working in and around excavations, work must be managed under the supervision of a competent person to ensure the following have been adhered to:
- Use of excavation supports to prevent the collapse of the side walls of an excavated area using:
–– Battering – which relies on the properties of the earth to form a stable sloping pile (i.e. the angle of repose).
–– Shoring – which uses artificial support for the side walls of an excavation where the angle of repose in the excavation is greater than the natural angle for the type of material.
- Barriers may be required to protect the edge of an excavation to prevent falls of people, materials, and vehicles. Fencing and hoarding may also be required to protect both employees and members of the public.
- Ladders provide the main means of access to and egress from an excavation. They must be suitably secured to prevent undue movement and extend five rungs above the excavation to give a secure stepping off point.
- Crossing points in an excavation should be at designated points and be of the sound construction to support all types of vehicles and equipment. Gangways across excavations should have guardrails and toe boards.
- Lighting and warning signs warn of the presence of an excavation and of any special measures to be taken on entering a site. Signs should be clearly visible and there should be a good level of lighting.
- The need for personal protective equipment is determined by the nature of the work being carried out (i.e. breathing equipment in tunnels and shafts; face shields for welding work; hearing protection where there is excessive noise) but hard hats are required at all times.
- Identification and marking of buried services and all cables by checking with local service providers, and safe digging methods, particularly when exposing cables and pipes, and using spades and shovels instead of excavators. Damage to cables should be reported immediately to the appropriate services.
- Positioning and routing of vehicles, plant, and equipment should be carefully considered to prevent objects from falling into excavations.