When is a trench high risk construction work?

In construction work, work in or near a trench or shaft with an excavated depth of more than 1.5 metres is high risk construction work under model WHS Regulation reg 291. That combination — construction work plus a depth greater than 1.5 metres — makes it high risk construction work needing a Safe Work Method Statement (SWMS) before the work starts. Depth is not the only trigger: in construction work, reg 291 also covers work on or near pressurised gas mains, chemical, fuel or refrigerant lines or energised electrical services, a tunnel, and work where powered mobile plant moves, at any depth. If none of these applies, a shallow trench is not high risk construction work, but the duty to manage the risk of ground collapse still applies.

Do I need a SWMS to dig a trench?

You need a Safe Work Method Statement (SWMS) when the work is construction work and the trench or shaft is more than 1.5 metres deep — that is high risk construction work under WHS Regulation reg 291, and the SWMS must be prepared before the work starts (reg 299). A shallower trench in construction work still needs a SWMS if it is on or near gas, electrical, fuel, chemical or refrigerant services, involves a tunnel, or is in an area where powered mobile plant such as an excavator moves — which is common for machine digs. Otherwise a SWMS is not specifically required, but you must still manage the risk of the ground collapsing and of a person or object falling in.

How do I prevent an excavation from collapsing?

Under the model WHS Regulations Part 6.3, a PCBU must manage the risk of ground collapse so far as is reasonably practicable. The main engineering controls are benching (cutting the walls into steps), battering (sloping the walls back to a safe angle), and shoring or shielding (supporting the walls with trench shields, props or sheet piling designed by a competent person). You must also keep excavated material (spoil), plant and stored loads back from the edge so the extra weight does not cause a collapse or material to fall in.

What is Dial Before You Dig?

Before You Dig Australia (formerly Dial Before You Dig) is a free service that helps you locate underground services — gas, electricity, water, telecommunications and other buried assets — before you excavate. Lodge an enquiry at byda.com.au, review the asset plans you receive, and have services marked, potholed or hand-dug as needed before machine excavation. Locating services is a key step in managing excavation risk and avoiding strikes.

What depth of excavation is safe without controls?

There is no depth at which an excavation is automatically safe. Any excavation can collapse — even a shallow trench can trap or bury a worker, because a cubic metre of soil can weigh more than a tonne. The duty to manage the risk of ground collapse and of a person or object falling in applies at any depth under model WHS Regulations Part 6.3. At 1.5 metres or more, the sides of a trench must be supported by shoring, benching or battering unless a geotechnical engineer advises in writing that they are safe (reg 306), and in construction a trench deeper than 1.5 metres is high risk construction work needing a SWMS. That does not mean shallower excavations are safe or unregulated.

Excavation & Trenching Safety Checker

Answer a few questions about your excavation. The tool tells you the ground-collapse controls to consider, whether the work is high risk construction work needing a SWMS (a trench deeper than 1.5 metres in construction), the Before You Dig step, and your safe access and egress duties.

Last verified: 21 June 2026Jump to calculator ↓

You must manage the risk of an excavation collapsing and of a person or object falling in, at any depth (model WHS Regulations Part 6.3). In construction work, a trench or shaft more than 1.5 metres deep is high risk construction work needing a SWMS (reg 291).

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