The Standard (AS2865:2009) defines a Confined Space as:
An enclosed or partially enclosed space that is not intended or designed primarily for human occupancy, within which there is a risk of one of more of the following:
a. An oxygen concentration outside the safe oxygen range
b. A concentration of airborne contaminant that may cause impairment, loss of consciousness or asphyxiation
c. A concentration of flammable airborne contaminant that may cause injury from fire or explosion
d. Engulfment in a stored free-flowing solid or a rising level or liquid that may cause suffocation or drowning
Confined spaces can be located above or below ground, and despite the name, they can be very small or very large. Confined spaces can have one single point of entry or egress, or multiple.
Open Top Spaces: Such as; pipes, pits, degreasers, sewers, shafts and ducts.