Prisons chiefs sure smoking will fade away without fire

More than half of the country's 8500 prisoners have signed up for therapy to ease the pain of a smoking ban.

From July 1 the country's 20 prisons will become smoke-free, and Corrections chief executive Ray Smith is confident the change will not bring violence or rioting from upset and irritable prisoners, as has happened overseas.

"The planning has been extensive over a 12-month period. Prisoners on the whole have taken it on board that they need to do something about it. A lot are on nicotine replacement," Mr Smith told the Herald.

But Mr Smith said many were also going cold turkey and staff were keeping tabs on potentially disruptive prisoners.

About 4700 prisoners so far had signed up for nicotine-replacement therapy, and more are signing up every day.

But that leaves about 1000 inmates who smoke and who have not signed up, based on the estimate that about two-thirds of prisoners smoke.

Corrections Association president Beven Hanlon has said prison staff were asking for riot squads to be on standby for the change.