Almost three years after Aboriginal man David Dungay died in custody most NSW prison staff have still not received physical training on the dangers of positional asphyxia.
Mr Dungay died after a struggle with guards in his Long Bay prison cell in December 2015.
He was restrained facedown by at least five officers in the "prone" position.
He screamed "I can't breathe" before becoming limp and vomiting. The 26-year-old couldn't be resuscitated, a coronial inquest into his death heard earlier this year.
At a budget estimates hearing on Tuesday, Corrective Services NSW Commissioner Peter Severin admitted just a few staff had recently begun physical training regarding the dangers of positional asphyxia.
"The physical training, where we actually take the staff through the physical aspects of the application of those techniques, has not commenced until very recently," Mr Severin told the legal affairs hearing.
Further quizzed on how many officers had received physical training, Mr Severin took the question on notice.
He said relevant officers had received some written advice concerning positional asphyxia "pretty much straight away" following Mr Dungay's death.
Greens MP and committee member David Shoebridge says the delay in providing adequate training suggests a "systematic failure" in the NSW prisons system.
"It's a matter of life and death and it hasn't been addressed," Mr Shoebridge told AAP.