Power plant gas leak scare
The Ngawha geothermal power station near Kaikohe has been declared safe after a buildup of pressure in a safety valve and the possible release of pentane gas.
"There was 30,000 litres of pentane in the system," Peter Heath, spokesman for plant operator Top Energy, said.
"The safety valve operated and we think it released some of it.
"We don't know at this point how much, if any at all. That's part of the investigation we're undertaking."
The investigation would look for the reason the safety valve operated, Heath said.
"The pressure valve would have opened to the atmosphere, [but] whether it actually released anything into the atmosphere we're not sure."
The plant shutdown happened about 5.30am and the Fire Service declared it safe at 7.30am.
Pentane was lighter fluid and had a very low flash point.
"It catches fire very easily. It doesn't take much heat or much friction to create a spark," Heath said.
"If pentane had been released there could have been a potential risk of explosion."
If any had been released into the atmosphere, it would have dissipated. The power station was also in the middle of a large forest.
The way the incident was dealt with was "pretty much a textbook exercise", Heath said.
"There was one guy on site," he said.
"The alarm went off. He did exactly what he should have done. He closed it down. He called the Fire Service."
Emergency services were called to the geothermal station following a report of an explosion.
However it was no more than a loud bang, Top Energy chief executive Russell Shaw said.
"We are concerned that this incident occurred but delighted that our emergency procedures appear to have worked as they should have," Shaw said .
"We're particularly proud of our duty staff member and the local fire service who ensured that this was a textbook response to the incident."