Forty-seven people were on Whakaari when it erupted on December 9, 2019 - 22 people died and many others suffered serious injuries.
WorkSafe New Zealand has opposed NEMA's application to dismiss the charge.
Yesterday in the Whakatane District Court Judge Evangelos Thomas heard legal arguments by the agency's lawyer Victoria Casey QC.
Casey argued that the WorkSafe charge laid against her client was "wholly misconceived" and it was not feasible that a conviction could be achieved at trial.
She argued NEMA was not caught by Section 36 (2) of the Health and Safety at Work Act and WorkSafe had "confused" risk management functions with issues of public occupational health and safety.
"NEMA says WorkSafe has fundamentally misunderstood civil defence emergency management and fundamentally misunderstood who NEMA is and what it does."
Casey said the accusation that NEMA, a small agency of about 60 staff, were in some way responsible for the deaths and injuries of 47 people "weighs heavily on them".
But WorkSafe's decision to charge NEMA was "fundamentally flawed" particularly, in describing the Crown agency as a PCBU or a person conducting a business or undertaking.
She said NEMA was a Crown agency and its function was in national crisis response and national policy advisory role, and not a day-to-day operational risk reduction role.
She argued NEMA was being "unfairly targeted" by WorkSafe when it was the civil defence emergency management group which actually had the operational functions.
Casey said WorkSafe's suggestion that NEMA had responsibilities as a lead agency to undertake a health and safety risk assessment for Whakaari sat well outside its scope.
"It is not NEMA's role to undertake a public health and safety operational function.
"NEMA's function is very much as part of the national security system but at a policy and advisory role level within the framework of civil defence emergency management."
Casey said NEMA was not responsible for day-to-day risk assessment of hazards or day-to-day communications with tourists, tour operators and individual landowners.
However, WorkSafe's summary of facts seemed to suggest NEMA could have asked for more information from Geological and Nuclear Sciences (GNS) about the risk.
"There seems to be subtle hints and whistles in the summary that NEMA should have issued a national warning [an eruption was imminent] but failed to act, which is deeply unfair and hurtful to the staff concerned."
There was no failure by NEMA, she submitted.
Casey said none of WorkSafe's own critical expert witness briefs of evidence alleged GNS should have done something more either.
She said none of WorkSafe's monitoring and forecast expert witnesses had challenged the science and analysis of the risk on the day of the eruption, nor GNS's actions in terms of its response.
"In fact, a critical expert's evidence was that there was no single warning sign that the explosive eruption we have here was imminent, requiring a national warning or advisory in the lead-up to the eruption."
Casey said there was no contest that the "science was correct" and it was as good as it could be in terms of GNS's risk assessment on the day of the eruption.
"No matter what conversation NEMA had with GNS or any suggestion that a national warning or alert should have been issued was answered by an interview RNZ had with a GNS scientist two days after the eruption," she said.
Casey said the scientist confirmed that despite the alert level being raised, they had intended to visit the island the day after the eruption took place.
"WorkSafe is entirely misconceived in alleging that NEMA's role is as a lead agency for risk reduction for volcanoes.
"And WorkSafe's suggestion that NEMA is mandated to pass on GNS risk assessment information to the public, tourism operators and individual landowners is not correct.
"There is a clearly a policy and operational functions divide here."
To hold the agency criminally responsible for regulatory failures outside the scope of its role and functions was "untenable" under the law, Casey said.
The others charged were: the island's owner Whakaari Management Limited and its directors Andrew, James and Peter Buttle; GNS Science; White Island Tours Limited; Volcanic Air Safaris Limited; Aerius Limited; Kahu NZ Limited; I D Tours New Zealand Limited; and Tauranga Tourism Services Limited.
The remaining 11 defendants have all pleaded not guilty and a four-month trial has been set to start in July 2023.
The charges do not relate to events on the day of the eruption, or the rescue efforts.
Today WorkSafe's prosecutor Kirsty McDonald QC will respond to those submissions.
