The Corrections Department is warning prison officers to keep their cool, following the death of a colleague at the hands of a prisoner.
A prison guard was assaulted at 1pm on Saturday as he and two other guards unlocked an cell.
Jason Palmer, 33, married, with two children, died in Middlemore hospital on Sunday.
He was the first prison officer in New Zealand to be killed on duty.
Chief executive Barry Matthews told Morning Report that officers have been instructed to behave professionally. He said the officers have accepted that, but "they are angry".
Mr Matthews said the attack was impulsive and risk is part of a guard's job. He said the department had taken several steps to reduce the dangers, including the introduction of safety equipment.
The Corrections Association says Spring Hill was built for low to medium security inmates, but has been housing more dangerous prisoners.
The department says it is not aware of the union raising concerns about Spring Hill.
Corrections Association president Beven Hanlon told Morning Report the circumstances surrounding Mr Palmer's death were completely avoidable.
He said the prison should have created a management plan for the prisoner, who had recently been classified as maximum security.
Mr Matthews says the prisoner had been segregated and was being handled by three guards, because of the risk he posed.
Spring Hill prison opened on 27 September, 2007.
It was the venue for the launch of new safety equipment on 26 February. Body armour, spit hoods and batons were being supplied to all prisons, at a cost of $1 million.
Comment by minister
Corrections Minister Judith Collins says it appears officers at Spring Hill Prison did everything correctly when dealing with the inmate.
She told Morning Report there's a limit to how well guards can be protected and if a prisoner decides to behave aggressively, there's little they can do.
However, Ms Collins said she wants to ensure there were no warnings that should have been noted or were not dealt with.
She said officers at Spring Hill should not blame themselves for Mr Palmer's death.