Prison expert defends Don Dale gassing

A prison expert has defended the tear gassing of six boys at Don Dale Youth Detention Centre but says putting them in spit hoods and shackles was an unreasonable use of force.

The teens were tear gassed in August 2014 after one escaped his solitary confinement cell and began trashing an exercise yard, the Northern Territory Supreme Court heard on Wednesday.

Detainees were then transferred to Berrimah adult prison and were shackled, handcuffed and spit-hooded.

Four boys, who cannot be named for legal reasons, are suing the NT government over their alleged mistreatment, arguing it amounted to assault and battery.

Assistant Corrections Commissioner for the NSW North West Region, Colin Kelaher, wrote an expert report on the Don Dale incidents, which have sparked national outcry and a royal commission.

Under cross examination by the barrister appearing for the teens, Kathleen Foley, Mr Kelaher justified the gassing as a reasonable measure to combat the growing unrest.

"The whole incident could have been uncontrollable if it was left to go on," he said.

"Given the nature of the destructive behaviour at the time the incident unfolded, I don't see any issue with the minors being treated any different than an adult."

In his 30 years of experience in corrections, Mr Kelaher has been directly involved in the deployment of tear gas once, and hasn't been trained to use it since 1994.

The court heard that two detainees who were gassed in their isolation cells had asthma, while one boy was exposed to the gas for eight minutes.

Mr Kelaher said the asthma sufferers should have been removed from the area as quickly as possible and given medical assistance.

But he added that knowing some boys had asthma wouldn't have stopped sacked NT Corrections Commissioner Ken Middlebrook from using the gas, given the escalating situation.

Ms Foley said in a separate incident in April 2015, officers held one plaintiff face down on the ground for 30 minutes with his hands handcuffed behind his back and his legs held up towards his bottom.

The boy had allegedly feigned a punch at an officer, spat at others and refused to go back to his room before being spit hooded and restrained.

Mr Kelaher said such an act would have been "totally unacceptable."

"It sounds to me more like a punishment than normal use of force to stop certain behaviour," he said.

The case before Justice Judith Kelly has been adjourned until October 17.