What is the importance of the Excavation tab in the Permit to Work (PTW), in OHS Online?
A very good question! The Excavation tab of the PTW must be selected whenever any excavation work is required for the work being done for the PTW. Excavation work is considered 'high risk' because every year people are killed when working in excavations or as a result of excavation work being carried out.
DANGERS ASSOCIATED WITH EXCAVATION WORK
Common dangers and risks associated with excavation work include:
1. Underground services and cabling - underground services and cables present a very real danger to excavations. These can easily be disturbed and damaged during the course of excavations, causing exposure to electricity which can result in arcing, fire or electrocution. At the same time gas could be released which could ignite or explode. Alternately, communication services, such as fibre cables can be damage, interrupting important services. Therefore, it is very important that checks are made before excavation work takes place, to ensure underground services are not impacted on.
2. Collapsing excavations - excavations can often collapse because of the nature of ground and ground conditions in which they are constructed. Any excavations need to have adequate supports in place to prevent collapse and be inspected regularly for any signs of degradation or after instances such as heavy rainfall or falls of earth or rocks.
3. Materials falling - materials such as excavated soil, rocks, etc can easily fall into excavations or cause an excavation to collapse due to their weight and stability. Edge protection and supports need to be in place for excavations and considerations made as to where loose materials should be place in relation to excavations.
4. Persons & vehicles falling - excavations present a real danger for persons or vehicles to fall into them, causing serious injuries or worse. Edges of excavations need to be protected with substantial barriers and excavation areas need to be cordoned off and adequately signposted to warn persons of their dangers.
5. Undermining other structures - excavations can often undermine other structures such as nearby buildings or walls or scaffold footings. Excavations need to be planned in such a way that any nearby structures are factored in and their dislodgement avoided.
6. Ground and surface water inflow - excavations can often be undermined by the permeability of the ground, allowing water to flow into excavations below the natural groundwater level. Supports on these occasions should be designed to control the entry of groundwater.
THE PARTICULAR DANGERS AND CONCERNS OF UNDERGROUND SERVICES
Of the various risks associated with excavations, the risks posed by underground services are of particular significance because these services are often being provided to other users in the area, which means there is the potential for much wider effects to be felt. If careful planning of excavations is not undertaken or due care not taken when conducting excavation activities, these underground services can easily be disturbed or damaged. Common underground services which may be affected include:
1. Electricity - disturbance or damage to underground electrical cables can be particularly dangerous because these often carry high voltages through them. Their exposure can result in death by electrocution or major burns. Common injuries occur to persons using pneumatic drills within half a metre of the surface.
2. Gas - disturbance or damage to underground gas lines can be particularly dangerous because the leaking gas could be toxic or it could be flammable, resulting in fire breaking out or an explosion occurring. In some cases, the ignited gas can return back along the line to other gas recipients, causing explosions there too.
3. Water - disturbance or damage to underground water lines can cause interruption of supply and result in significant costs to repair.
4. Telecommunications - disturbance or damage to underground telephone or fibre optic cables can cause interruption of supply, affecting the ability of businesses to operate effectively and result in significant costs to repair.
The Excavation tab helps to ensure formal checks are made and associated safety precautions are taken for any excavation work, in order to ensure the work is conducted under safe working conditions. Through these measures, any necessary check measures required to prevent unnecessary damage to underground services and subsequent service interruptions, can be made and suitable precautions put into place.