NSW prison leaders are assuring the public staff are being trained after it was revealed there has been no physical education on asphyxiation three years after Aboriginal man David Dungay died.

Mr Dungay died after a struggle with at least five guards in his Long Bay prison cell in December 2015.

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.

He could not give an exact number on the number of staff taken through the physical training exercises.

But a spokeswoman later said Mr Dungay's death led to changes in policy and a new course on the use of force was being rolled out to Immediate Action Teams.

IAT officers were involved in Mr Dungay's death.