The Department of Corrections is tightening security on external prison work parties to stop inmates from doing a runner.
The department was concerned by the number of prisoners who escaped from work parties in recent years, acting prison services assistant general manager Leanne Field said.
"It is our duty to ensure that prisoners remain in our custody and when prisoners escape we have failed in our duty. This is unacceptable not only to ourselves but the public of New Zealand."
Overall the number of breakouts had declined significantly, with about 150 escapes in 1985/86, compared to 23 in 2007/08.
Since July 1 2008 there had been 10 escapes, five of which involved a prisoner walking away from their work party.
To reduce the risk the department had reviewed the suitability of every prisoner employed outside the prison, and a small number of prisoners had their employment terminated, Ms Field said.
"We are also critically looking at our security classification system to ensure that it is adequately capturing the risk a prisoner presents outside the prison perimeter, including the risk of them escaping."
The new systems would only work if staff followed the procedures in place, she said.
To ensure this happened the department was improving its audit processes, which involved regular observation to ensure staff compliance.
"We have also strongly reinforced to managers and staff that deliberate failure to follow policy is inexcusable and will lead to disciplinary action."
Work parties played an integral part in reducing re-offending by helping to provide basic employment training and prepare prisoners for release, Ms Field said.
"Unfortunately there will always be a prisoner who acts in a way that is entirely unpredictable. We are committed to limiting this risk."
