It was about lunch time when the young construction worker's father, Graham Bush, was told over the phone his boy had been involved in a ''serious incident'' and was being rushed to Canberra Hospital.

Jayson had fallen more than five metres down a ventilation shaft at his workplace, the building site of the upmarket Nishi development in central Canberra.

It is the type of phone call that too many families in Canberra and the region have taken over the past 12 months, say work safety authorities and the building union.

Jayson is recovering in hospital, with spinal injuries, broken ribs and slight bleeding on the brain and his doctors are worried about an air bubble trapped in the young builder's chest cavity.

Mr Bush said that his son found himself at the bottom of the shaft after being knocked unconscious by the fall which is believed to have occurred at about 10am, earlier than first reported.

''The first thing he thought was either I'm dead or I'm blind because when he opened his eyes up, there was nothing,'' Mr Bush said

''He couldn't cry out because he couldn't get any air into his lungs and he couldn't call triple 0 because he was down in the basement and he couldn't get any phone reception. ''So you can imagine the terror - with the pain he was in and the injuries that he's got. For two hours, we think he was down there in pitch darkness and when he got through to triple 0, they were asking him which unit he was in, which street he was on.''

The ACT government ordered an inquiry last month into workplace safety in Canberra's building industry after four workplace deaths, three of them in the civil construction sector since December, and numerous serious injuries.

Mr Bush, flanked by construction union officials, said yesterday that he wanted a full investigation into Jayson's accident and why he was assigned to a cutting job at the top of the deep shaft on his own.

''These boys are not soldiers, they're not going to war and when they go off to work in the morning, you expect them to come home,'' Mr Bush said. ''Jayson's first reaction when he woke up in hospital was to say to me 'I told them I couldn't do that thing by myself'.''

WorkSafe ACT, called to the Nishi project several times this year, is investigating the incident.

Work Safety Commissioner Mark McCabe said bosses were required to report serious workplace accidents and injuries.

''Reporting these matters to WorkSafe ACT immediately is imperative,'' Mr McCabe said yesterday.

''If WorkSafe becomes aware of serious incidents through some other means, often the scene of the accident will have been disturbed and any investigation by the regulator will be compromised.''

Mr McCabe said employers who failed to comply with the law faced fines of up to $50,000.