Trenching and excavation work

Construction and excavation sites can expose persons to the risk of injury from a wide range of hazards including trenches, holes, lift shafts, sewers, wells, tanks and stairwells.

Trenching and excavation work have the potential to expose persons to the risk of injury from falls from height. Encapsulation, where workers are buried as a result of the collapse of trench walls, is also a serious and severe risk that must be controlled. Even shallow excavations can be trip and fall hazards, although the likelihood of injury when a person falls increases with the depth of the trenching or excavation work.

Prior to excavating, a site investigation should be carried out to determine:

nature of the ground such as soil type, rock and water table
possibility of flooding from any water source
the existence of underground services such as gas, electricity, pipelines and sewers (Before You Dig Australia)
proximity of other excavations and other point sources of instability
the possibility of natural or artificial hazards such as ground contamination
static/dynamic loads for example, buildings, traffic and ground vibration

A documented risk assessment for all trenching/excavation tasks should be completed based on the results of the site investigation. Consideration should be given to factors such as how long the excavation will be left open and the security of the excavation, both during work and when left unattended.

The outcome of the risk assessment will provide an insight into the appropriate control measures for eliminating or minimising the hazards in the mandated order.

The Work Health and Safety (Excavation Work Code of Practice) Approval 2020 sets out a range of measures which ensure work safety in relation to excavation work.

Reducing the risk

Control measures to prevent persons being injured from a fall from height during the excavation work must be provided. Controls should be properly installed and maintained until the work is completed or until a further risk assessment identifies that there is no longer any risk of persons falling into the excavation.

Some control measures that should be considered are:

the application of physical fall prevention measures
isolating the trench or excavation by the use of perimeter fencing, barricades, barriers, screens, handrails and trench covers, which are capable of preventing access or preventing a person from falling
pedestrian detours which should be clearly defined and protected
the provision of a safe means of movement between different levels of excavation
the use of intermediate platforms for deep excavation
backfilling the excavation as work progresses
workers are provided with information, instruction and training relevant to their trenching or excavation work.

When barriers are used they should be placed at least 2 metres from the edge of the trench where possible. They should be highly visible and capable of remaining in place during adverse weather conditions. Safety type tape is not an adequate physical barrier as it hard to see in low light conditions and can be easily broke. Unless they are specifically designed for the purpose, barriers should not be used as guardrails.

Any work carried out involving a trench or shaft excavated to a depth of 1.5m or greater is deemed to be high risk construction work and requires a safe work method statement.

When excavation work is being conducted in close proximity to underground utilities assets, further controls should be put in place to reduce the risk of an asset strike by excavation plant. The utilities provider should be advised of proposed works and any requirements of the utilities owner should be incorporated into the risk assessment and safe work method statement for the excavation work.

All trenching and excavation operations should undergo a daily checklist system to ensure that safety requirements are observed including:

no person enters an unsupported section
trenching supports are appropriate to the conditions (i.e. The need or otherwise for trench shields, close sheeting, benching or battering)
spoil heaps are properly positioned at least 0.9 metres from the edges of the trench
safe ladder access is provided into the trench, with 2 access points required for trenches greater than 8 metres long
where reasonably practicable, appropriately maintained stairs cut into the excavation
all workers wear safety helmets
no person is working alone in an excavation
persons do not remain in close proximity to where an excavator is operating
persons to wear high visibility vests when working on or near machinery
the excavation is protected by Para webbing barricades
workers in excavations are not exposed to an accumulation of hazardous fumes including fumes from petrol or diesel vehicles
no on enters a trench that is not shored or battered.