New Zealand hospitals spent more than $14 million treating the victims of the Whakaari / White Island eruption.
The Accident Compensation Corporation, however, has agreed to reimburse the five district health boards for the inpatient bill. This was in part thanks to the triggering of a never-before-used clause for a mass burns event.
Twenty-one people died from their injuries after the submarine volcano erupted on December 9, while tourist groups were visiting.
Whakaari / White Island is 48km off the Bay of Plenty coast and victims had to be rescued by boat and by helicopter for lifesaving treatments.
Survivors were left with full-thickness burns, blast injuries and severe respiratory damage.
The Ministry of Health provided the final hospital cost figures and payment agreement to NZME, in response to questions this week.The costs covered the treatment of 35 victims at hospitals, nine of whom later died, leaving 26 survivors in total.
ACC originally agreed to pay up to $20m to refund DHBs for eruption-related hospital costs.
But that was in March when it was still unclear how long some victims would remain inpatients.
By April 6, all survivors in New Zealand had been discharged, although other repatriated victims remained inpatients in Australia.
The final cost of Whakaari / White Island inpatient care in New Zealand hospitals fell more than $5m below ACC's cap on April 6, at a total of $14,523,784.
The Bay of Plenty DHB had the smallest costs, coming to $521,908, but a spokeswoman declined to elaborate on what the costs were.
An Official Information Act response provided to NZME earlier this year said the hospital's air filters had to be replaced in the days after the eruption because of the fast accumulation of ash and sulphur after victims arrived in the building.
It also said the emergency department and acute care unit had to be cleaned down, including all equipment and beds.
Pillows and mattresses had to be replaced because they were soaked in body fluid and locums were brought in to cover for more than 20 staff who took stress leave in the weeks after the eruption.
The Counties Manukau District Health Board manages the national burn unit and spent $10.164m treating Whakaari victims in Middlemore Hospital.
These costs included paying nurses, doctors and other health professionals' labour and facility costs for operating theatres such as food, linen, ICU, and ward beds.
Supplies also significantly contributed to the bill, including skin used for grafts, as well as drugs and consumables such as wound dressings.
ACC is covering survivors' ongoing treatment and rehabilitation costs in New Zealand but not overseas.
So far those costs have come to $723,518.
This includes accidental death entitlements, transportation costs, weekly compensation and helping survivors return to independent living.
"These costs will continue to grow as further rehabilitation services and support are delivered to clients over the coming months and years," Mike Tully, ACC's chief operating officer, said.
Although 35 people were admitted to hospital after the Whakaari eruption, the overall inpatient expenses were more than twice those from the Christchurch mosque shootings in March last year when 48 people were admitted to hospital.
The attacks that left 51 people dead led to $6m in inpatient costs.
Unlike the Whakaari eruption victims, who were sent to burn units across the country, all but two of the 48 hospitalised mosque shooting victims remained on in Christchurch Hospital wards.
However, ACC did not reimburse the Canterbury DHB for the $6m.
The Ministry of Health gave $3m extra funding to the DHB but the other $3m was added to the Canterbury board's deficit.
Tully said the corporation's Public Health Acute Services agreement with the Ministry of Health had a clause allowing for extra ACC payments for "complex burns cases caused by a significant event".
"This clause acknowledges that burns can be costly to treat. The eruption was the first time this clause has been triggered."
He said it was "the only such clause in the agreement that allows for additional payments".
"No other mass casualty events are covered", meaning mass shootings weren't specifically covered.
However, the corporation does cover ongoing treatment, rehabilitation, counselling and financial support for the shooting victims.