The survivor of the fatal Orewa College boiler explosion fears there are ticking time bombs in most Kiwi schools.

Engineer Robin Tubman, 51, says the Government used to oversee school boiler maintenance, ensuring they were safe.

But now lay school board members are in charge, often using untrained people to check boilers sporadically - potentially putting kids' lives at risk.

"If schools aren't keeping the boilers maintained properly then there could be bombs in every school," Tubman says.

Secondary Schools Principals' Association president Patrick Walsh shares Tubman's fears and has written to Education Minister Anne Tolley to ask her to take back responsibility for schools' Health and Safety issues. Tolley says she has asked the Education Ministry to look into it.

Orewa College's board chairman, Phil Pickford, and a Labour Department spokesman would not comment on the matter before the Orewa College board of trustees appears for sentencing in the North Shore District Court on Tuesday.

The explosion happened on June 24 last year - just before the school bell went at 3pm.

The board previously pleaded guilty to charges laid by the Department of Labour, including failing to take all practicable steps to ensure the safety of its employee, caretaker Rick Nel who died, and engineering contractor Tubman.

Nel, who was near the boiler when it exploded, received 80 per cent burns to his body.

Tubman suffered serious injuries. He told the Herald on Sunday that media reports at the time were inaccurate; he was not fixing the boiler that day. Instead, he had been fixing a leaking pipe in a classroom nearby, but was walking 3m from the boiler when it exploded.

The explosion threw him back 2.5m into a van while an object, believed to be flying metal, ripped off a third of his skull. Bone particles pierced his brain and had to be removed by surgeons. His abdomen and legs were burned and his left arm was pulled out of its socket.

"Luckily I have no memory of the whole day," says Tubman, who was rushed to hospital by helicopter. He can even joke now that the ordeal he went through was "mind-blowing".

Wife Noriko Tubman says she was told later that doctors had debated that day "whether it was worth operating - they didn't think he would make it".

After the operation, she could not let their three children see their father for weeks because through the bandages and swelling "they wouldn't recognise who he was".

Robin Tubman has since had four operations, including on his burns, head (which has been susceptible to infection), and to remove blood clots.

He has yet to regain the use of his hand and fully recover from the brain damage. This week he was told he will have surgery next month to insert a new plastic skull, specially made in Australia.

Noriko says the ordeal has meant she has not yet been able to complete the last semester of her training to become a teacher - "her dream" - because of financial pressures and having to care for her husband.

The family struggle to survive on 80 per cent of Tubman's former pay received through ACC. The school has apologised to the couple, who hope for compensation.

But what they really want is public understanding. People have been pointing and joking about the helmet Tubman has to wear to protect his head.

"I have to wear it. If someone hit me on the head it would probably kill me," he says.