Prison staff representatives say attacks on staff are far more serious than official figures indicate.
Unions say the way serious assaults are defined means even stabbings are not necessarily included.
The Department of Corrections says an assault on a staff member who receives physical injuries that does not require an overnight stay in hospital - such as bites or a bloodied nose - is classed as non-serious.
But Corrections Association national president Beven Hanlon says some prison officers have been stabbed and others knocked unconscious, yet the assaults have not been classed as serious.
"We've had a prison officer stabbed and that hasn't been classed as a serious assault but the prisoner ended up getting eight years added to his sentence because he was trying to escape at the time.
"There are a large number of events that have happened. We've had officers knocked unconcious and that's not considered a serious assault.
"It's just crazy - the stipulation they have for a serious assault is just too rigid."
Public Service Association national organiser for prisons, Graham Cuffley, says the Department of Corrections figures do not reflect reality.
"One to two a day actual assaults would be within the ball park figure but that of course doesn't include threats of assaults.
"The current recording mechanisms in no way give the public a clear picture of the level of violence facing prison officers every day."
The Minister of Corrections, Anne Tolley, says there were 18 serious assaults on staff in the 2011/12 financial year, 13 last year and one so far in the current year.