Hazard Related Topics
The CDM 2015 Regulations makes the following definition: "excavation" includes any earthwork, trench, well, shaft, tunnel or underground working.
Working in excavations is an extremely dangerous operation which can be made safe by an awareness of the hazards and the precautions to be taken and careful management of the process.
The hazards and risks are usually:
- Collapse of the sides of the excavation.
- Materials falling onto the people working in the excavation.
- People and vehicles falling into the excavation.
- The undermining of nearby structures causing their collapse into the excavation.
- Damage to underground services during excavation work causing electrocution, explosion, gas escape, flooding etc.
- Ingress of water causing flooding
The works should be carefully planned and carried out. Ensure that equipment and materials needed are available on site before work starts. Ensure that the work is directed by a competent supervisor and the works are inspected daily by someone who understands the risks and precautions to be taken. At least once a week the excavation should be thoroughly inspected and also after any event which may affect the temporary support. Such inspections should be documented.
The precautions to be taken are:
- Trench collapse should be avoided by battering the sides to a safe angle or by supporting them with sheeting or proprietary support systems. Support should be installed without delay as the work progresses. Ensure the workers are competent and experienced as far as possible and that they have clear instructions.
- Excavated spoil, plant or materials should not be stored close to the sides of excavations as loose material can fall in. The extra loading can make the sides of the excavation more likely to collapse.
- Prevent people from falling into excavations by substantial barriers around the edges. This must be done if the depth exceeds 2 metres but is recommended for excavations of lesser depths.
- Prevent vehicles from falling into excavations or surcharging and causing the collapse of the sides of the excavation by keeping them out of the area. Baulks and barriers can be provided for this purpose and should be painted to be easily visible. If vehicles have to tip materials into excavations then they should be prevented from over-running into the excavation by using stop blocks.
- Provide safe access in and out of the excavation.
- Hazardous fumes should be considered. Diesel and petrol engined equipment should not be allowed into excavations without arranging for exhausts to be ducted away or forced ventilation to be used.
- Cable and / or pipe plans and service plans should be used to locate underground services which should be marked on the ground and where practicable digging should take place as far as possible from them. Use cable and pipe locators during the course of the excavation work. Great care should be taken to ensure that mechanical means of digging are not used within 0.5 metres of underground services and spades and shovels should be used instead of picks and forks which are more likely to pierce cables. Once services are located and exposed they should be supported. Both new and existing services should be permanently marked by the use of appropriate tapes over the service and by placing permanent markers above ground indicating the service type, depth, route etc.
- Precautions should be taken against flooding by installing efficient means of pumping out the excavations ensuring that the outflow from the pump does not cause flooding problems elsewhere.