Three male detainees climbed to the roof of Ashley Youth Detention Centre on Friday and caused an expected $20,000 in damage during a three and a half hour stand-off, highlighting the site's safety concerns.
A $16,000 camera was damaged, along with solar panels and antennas before the youth were brought down off the roof and separated.
An October report by Custodial Inspector Richard Connock critised the centre's security, including its lack of a screening device on-site to prevent the entry of prohibited items.
Health and Community Services Union assistant secretary Robbie Moore said during the incident there was several threats made to staff.
He said the centre was a very old site and was in need of much needed upgrades.
"We've been raising significant safety issues there for a long time now," he said.
"I guess this incident further highlights how important it is that staff and children need a safe environment and ...further highlights the need to take action around safety.
"Which includes looking at safety issues but also infrastructure and other issues that need to be improved at Ashley."
It was a 2018 election promise of the Hodgman government to upgrade the facilities and tenders for the $7.3 million redevelopment closed on November 20.
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Mr Moore said staff were grateful the incident had been resolved but the lack of investment by the government was detrimental to staff and children.
"What they did was instrumental in resolving that, I guess it highlights the intense environment that they are working in," he said.
"It really needs an overhaul...it was made decades ago and is out of date.
"It really needs a proper refurbishment with modern technology and infrastructure to create a safer environment for staff and children."
A state government spokesperson said a planned major redesign and upgrade would ensure it was fit for purpose and modern.
"We take the safety of staff and offenders extremely seriously however, as the matter is currently being investigated it would be inappropriate to comment any further," they said.
"We are redesigning the youth justice system and the AYDC to give young offenders the care and skills they need to lead positive lives when they return to our community."
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