The comments came after a spate of assaults on staff members working in the facility this year.
The former OCF officer, who declined to be named, told the Otago Daily Times management was failing to keep employees and prisoners safe.
"It all comes down to safety. Management are not adhering to basic safety.
"It’s not safe for the staff and not safe for the prisoners, particularly if they’re housed with a volatile cellmate," he said.
The former employee said he resigned in 2019 when the situation started becoming more volatile and he was still in touch with a number of current employees.
He said the facility should not have the number of high-security prisoners it had at present.
"Management should be saying no to so many high-security prisoners.
"The place is not designed for that and what they’re currently doing is not working."
He said he understood why North Island inmates sent down to the OCF would not want to be so far from their own families and support systems.
"They don’t want to be on a totally different island ... so they can play up, which sometimes extends to assaulting staff to hopefully end up in a North Island prison."
High turnover of staff was a problem when he was an employee and continued to be so today, he said.
Losing so many experienced front-line staff members meant there was an influx of new staff who all needed to be trained at once.
"You need a certain number of people to open a cell door, two or sometimes more — there are times where that was happening with only one person. I don’t think I need to explain why that is a bad idea.
"I wouldn’t be surprised to see a column of smoke on the horizon one day ... I’ll be thinking ‘yep, that’s OCF, it’s gone’."
Department of Corrections deputy commissioner for men’s prisons Neal Beales said Corrections increased the number of high-security beds at the OCF in late 2022.
"We consulted on these changes with unions and ahead of the reconfiguration we carried out construction work at OCF to install additional security features.
"We also built new rosters to ensure the correct number of staff are rostered on and we monitor and review tensions daily and increase support in the units if required."
Mr Beales said a larger group of high-security prisoners benefited the other inmates as it allowed for more rehabilitation programmes.
Mr Beales said the OCF had recently received prisoners from the North Island to support prison population management across the country.
"Decisions to move any prisoner are made on a case-by-case basis.
"Where men are moved away from their families, we ensure they can maintain contact through increased frequency of virtual visits."
When the OCF started receiving more high-security prisoners, construction work was carried out to install additional security features.
He said assaults on Corrections staff were unacceptable.
"[Our staff] deal with some of New Zealand’s most challenging people and do an exceptional and brave job in often very difficult circumstances.
"We are committed to taking all precautions possible and following best practice and advice to help keep our prison environment safe."
He said staff retention had improved since last year.
"Staff turnover stands at 9.5% compared to 14.2% at the same period last year and the OCF turnover rate is below the national average at 8.1% over the past 12 months with the average tenure at over eight years."
