People usually think of working at height as only being a risk when working above ground. But you don’t necessarily need to be up high for a fall to occur. Falls from the ground to a level below, even ones inside an existing structure are equally high risk, especially in areas which are not designed for human occupancy and maybe have ingress/egress limitations. As such, the definition of what is, or isn’t, a confined space is not so clear cut.
Confined space environments come in a variety of guises including vats, tanks, pits, pipes, chimneys, silos, sewers, shafts, wells, pressure vessels, trenches and tunnels.
The National Work Health and Safety Regulations (the WHS Regulations) and the Australian Standard 2865-2009 Confined Spaces have very similar definitions of a confined space.
The Regulations define a confined space as an enclosed or partially enclosed space that:
Working in a confined space is a high risk activity and the potential for incidents resulting in fatalities are compounded by the nature of the hazards present. Examples of the key risks include the potential lack of oxygen, high temperatures, explosive environments and the risk of airborne contaminants including gas, fumes and vapours. Other hazards include the risk of engulfment in flood waters, sewerage, grain, smoke or dirt from a trench collapse
So it is often more expedient to assume a space is placed in this category and manage the hazards accordingly rather than underestimate the risk and be left with safety compromised workplace.
All regulators have information on their websites regarding working in confined spaces. Consult with those locations to assess the requirements for your specific needs.