Bob,

The Act (at least in QLD) does define workplace and what a worker is (especially relevant is the last line)

A workplace is any place where work is, or is to be,
performed by—
(a) a worker; or
(b) a person conducting a business or undertaking.

Who is a worker
(1) A person is a worker if the person does work, other than under
a contract for services, for or at the direction of an employer.
(2) A person may be a worker even though the person is not paid
for work done by the person.
Had to study all this at Tafe a couple of years ago for work. At last it came in handy