The disability royal commission on Friday heard evidence from WA's inspector of custodial services, who reiterated his view Banksia Hill was run more like an adult prison than a centre for detaining children as young as 10.
Eamon Ryan earlier this year revealed some boys at the Perth facility had spent as little as one hour a day outside their cells, in violation of their human rights.
He told the commission he had been underwhelmed by the state government's response to his report, which also outlined a surge in self-harm attempts by detainees.
"It was a security response," Mr Ryan told the Perth hearing.
"I'm not being critical of that ... there were a heightened number of critical incidents (including) staff assaults and those sort of things.
"But there were also an increased number of self-harm attempts, suicide attempts, and it needed some sort of circuit-breaker.
"You can't wait six to 12 months to develop an operating model of care and get a consultant to do your philosophy and then fund that and train all the staff. It needed something immediate."
Mr Ryan said the situation at Banksia Hill had further deteriorated between his visit in January and the decision in July to transfer a group of disruptive boys to the standalone Unit 18 at the maximum-security Casuarina adult prison.
He believed there was a clear need for a trauma-informed model of care which could help to reduce the rate of critical safety incidents.
The inspector's report in April found 49 staff had left Banksia Hill since January 2021, an attrition rate of around 25 per cent.
Mr Ryan said the rate of workers compensation claims among youth custodial officers was also "extraordinarily high".
WA's Department of Justice, whose director-general will front the royal commission next month, declined to comment on Mr Ryan's evidence.
The inspector said conditions at Unit 18 remained volatile with reports of lockdowns and staff assaults.
He said WA was an outlier in having only one juvenile prison and detainees would have a better chance of rehabilitation if they weren't all grouped together.
The McGowan government has promised an on-country detention centre in the Kimberley, where youth crime has been a major issue in recent years.
A former detainee at Banksia Hill this week told the royal commission he had been brutalised by guards, denied phone calls and left to sleep naked on a concrete floor.
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