When Kelvin Rimmer turned on the television on Wednesday morning and saw SkyCity's new convention centre ablaze, his blood ran cold.
As a fireproofing contractor, he had personally signed off on parts of the construction site at the New Zealand International Convention Centre (NZICC) in Auckland's CBD.
"I'm still kinda petrified now," he said. "It's concerning when you have your signature on a building literally doing the thing you're trying to prevent."
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Rimmer, who has been in the industry for two and a half years, said he was now confident that the parts of the building he worked on "performed" as they should have - meaning that fire and smoke did not penetrate floors and rooms which had already been sealed off.
Working for fire protection company RedCrow, he helped fireproof the ground floor up to the third floor. The huge fire and smoke plume, which started on the roof on Tuesday, reached no further down than the fifth floor.
"There is absolutely no way that the fire could have gone below the [fourth] floor. It is physically not possible. It is airlocked, there is no way for it to do that."
But it was still a nervy few days for him and his colleagues.
"On Wednesday morning, my girlfriend said there was a building on fire and I thought 'that can't be good, I wonder what it is?'
"And it was in the middle of Auckland. The cogs started turning a bit, I know all the construction sites in the Auckland area.
"I turned the TV on, and it was the NZICC. All the fire engines, gathering around it. You feel like you walked away and finished the job, that the building is secure, everything is up to standard.
"Then to see that, it is such a stomach-wrenching kind of moment where you question yourself and think 'Did I do everything right?' "
Another contractor, Global Fire, was still in the process of sealing off the higher floors, he said. All of the main frame of the building had already been fireproofed, meaning the fire and smoke could not have travelled down the large pillars into lower floors.
Rimmer said fireproofing was a slow, complicated job which required closing off every tiny opening.
"If there is a pencil-sized hole in a wall, an average-sized room can fill up in three minutes. And that's enough to kill someone.
"It's not the fire that we really worry about when it comes to workers or disasters, it's more 'Can we prevent the smoke from stopping the people exiting?'. That is always the biggest concern."
While investigations are still under way, he said it appeared no workers had been prevented from getting out of the building by smoke. And it had not spread through the floors of the site.
"By the sound of it, we've done pretty good. We were pretty happy with everything."
Fire and Emergency New Zealand and WorkSafe are leading the investigations. It has already been reported that no automatic fire alarms were in place in the upper floors because they were still under construction.
Fletcher Building, which is building the centre, has said that blowtorches were being used on bitumen to seal joints and that is where the fire is believed to have started.
Rimmer said he was surprised at how far the fire spread if it was ignited by a blowtorch.
"It is completely remarkable that it grew to the stage that it did."