Insufficient resources and lagging infrastructure are undermining safety and security at WA's main maximum-security men's prison, a report says.
Chronic staff shortages are also contributing to the problems at Casuarina Prison, where concerns have been raised about the facility's ability to rehabilitate inmates.
Custodial Services Inspector Eamon Ryan noted WA's largest publicly run prison was being redeveloped, and is set to become the biggest in Australia with a capacity for more than 1800 inmates.
"The question has to be asked: how big is too big?" he said on Monday when his inspection report into the facility was tabled in state parliament.
Mr Ryan said the expansion would bring complications "associated with managing so many people and their needs".
The expansion project includes new high security, forensic mental health and high dependency units, an expanded infirmary and new accommodation units and support buildings.
These will be in addition to the current mainstream units, special protection unit and the alcohol and other drugs rehabilitation unit.
"Safely managing prisoners with so many diverse needs, conflicts and risks between them is a considerable challenge," Mr Ryan said.
He said many prisoners had mental and other health needs, as well as intellectual and cognitive impairments.
"The situation is exacerbated by the lack of meaningful and constructive activity in the daily regime, with high unemployment and underemployment," he said.
Mr Ryan said the prison's infrastructure and resources were not able to cope with the current number of inmates who were not being provided with meaningful activities like industries, recreation and education.
This was found to be undermining safety and security at the facility, and its ability to rehabilitate inmates and prepare them to re-enter the community.
Chronic custodial staffing shortages driven by unplanned absences, like personal and workers' compensation leave, are an aggravating factor, with some officers saying it was also causing low morale.
WA's Department of Justice said the prison continued to operate effectively and efficiently during the expansion program.
"Successfully managing adult male prisoners in the specialist and mainstream population units is a testament to the proficiency of management, staff, specialists and peer support prisoners," Corrective Services Commissioner Mike Reynolds said.
Department director-general Adam Tomison said Casuarina held a unique position in the state's prison system.
"Casuarina management, staff and specialist service providers perform a critical role in handling the various risks and the Office of the Inspector of Custodial Services report acknowledges this," Dr Tomison said.
Casuarina Prison is located 37km south of Perth's CBD.
In addition to the mainstream prisoner population, it houses many of the state's most difficult-to-manage, high-risk and major-threat prisoners, as well as those placed in protection units for their safety.
The inspection did not include Unit 18, which is operated separately from the adult prison as a gazetted youth detention facility.
