Prison guards say a surge in the use of pepper spray at jails is part of attempts to reduce aggression.
The numbers of assaults reported in prisons has also been increasing.
In the 2016 financial year, there were just six recorded uses of pepper spray.
Last year, guards displayed their cans of the inflammatory agent - and prepared to incapacitate an inmate - nearly 900 times.
In many of the incidents recorded, just showing the spray can was enough to cool down a situation.
Corrections Association president Alan Whitley said the spray was not just to keep staff safe.
"The pepper spray also keeps prisoners safe as well," he said.
"If you've got a couple of prisoners fighting and you can't get them apart, you've got one prisoner that's beating on another prisoner, you can use pepper spray on him to get him off him."
Guards said there had been an increase in assaults in prison, and increased use of other forms of force.
The Corrections Association said threats to guards were also escalating
The Department of Corrections said 75 percent of prisoners had been convicted of violent crimes, and many inmates responsible for assaults were gang members.
RNZ
