The landscape was still so dangerous the head of the Defence Force had to sign a special exemption for the rescue operation, bypassing Health and Safety protocols and acknowledging the extreme risk involved.
Documents released by the Defence Force after requests by RNZ and other media give more details about the mission, in which eight people landed on the island and brought back six bodies.
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The eight members of the Defence Force ventured onto Whakaari/White Island in December, knowing there was a chance they could inhale toxic gases or have their skin burned by acidic sludge.
Such was the state of the volcano four days after the explosive eruption of 9 December, that had sent mud and rocks and a massive ash plume spewing from its crater.
The Defence Force was called in by the police early on in the operation, to plan the recovery. Three days after the eruption a window opened, and the mission was set for the next morning.
The Chief of the Defence Force, Air Marshal Kevin Short, was asked to sign a waiver declaring the recovery an operation that would bypass the Health and Safety at Work Act.
The documents describe why: "These operations include [using] specialist equipment within an atmosphere contaminated by toxic vapours and noxious chemicals, and complicated by a threat of future volcanic eruptions."
They detail that the recovery could not be conducted while adhering to Health and Safety requirements.
"Operationally there is an inability to totally eliminate the safety risks that are inherent in operating within a volatile volcanic environment.
"Specifically these limitations include the inability to: escape from the effects of corrosive chemicals; eliminate the risk of inhaling toxic gases beyond the use of personal protective equipment; pre-position medical staff in close proximity without exposing them to the same risks."
Short accepted the risks, notified Defence Minister Ron Mark of the move, and the operation was a go.
The SAS soldiers and two medics who were to take part made their way to Whakatāne, and rehearsed the full recovery operation.
That included working in the multi-layered protective suits with their own isolated breathing apparatus, how to use acid-neutralising pouches they were given for emergency first aid, and how to load the bodies onto the NH90 helicopters.
The team was given detailed information about the island's hazards and what they would find, gathered from assessments in the days following the eruption.
"High resolution hand-held imagery was collected, as well as electro-optic and infrared video," a planning document said.
"This included imagery of the crater and surrounding areas, the coastline, Te Awapuia Bay and vessels in the vicinity."
Detailed surveillance footage of the island collected before the recovery mission helped plan their approach once they reached the island, the document describes:
"Consideration would have to be given to the deep ash layer.
"Of note, upon further analysis of the imagery on board the aircraft, it detected a number of possible bodies.
"Throughout the 2.3 hours [surveillance] at White Island, no movement was detected by the crew."
The crew were told it would be a 15-minute walk to the bodies after being dropped onto the island, and a strict three-hour time limit was placed on the operation.
On the day of the recovery, police said the SAS team landed on the island just before 8.20am.
The news the bodies had all been recovered and moved to the HMNZS Wellington came through at 11.17am.
The recovery operation concluded just minutes before the team would have had to withdraw from the island.