Yallourn Power Station safety concerns are bad news as Australia enters long, hot summer
In the early morning gloom during mid-July, workers preparing for a shift at Yallourn Power Station in the Latrobe Valley hear an almighty crash. 
A 2.5-tonne metal support, known as a hangar, has fallen from the roof in one of the cavernous boiler rooms and landed on a walkway below.
It leaves grid metal, nearly 3 centimetres thick, mangled and bent.
A union organiser from the site said anyone standing underneath the hangar when it collapsed "would have been punched through the grid like mincemeat".
Mark Richards, the Victorian secretary of the Mining and Energy Union, was similarly blunt.
"It's not like dropping a tool on someone's helmet," he said.
"This is like dropping a truck on someone.
"There's not much chance of survival if someone happened to be in the wrong place at the wrong time."
For the power industry veteran, the fallen hangar was just one of several serious incidents that made him worry about safety at Yallourn, a 1,480-megawatt brown coal plant 140 kilometres south-east of Melbourne.
According to Mr Richards, others included a catastrophic failure of a fuel mill and a landslip at the adjoining mine.
He said any of those incidents could have been fatal.
"It's very, very concerning when you see structural failure such as this," Mr Richards said.
"[The] plant wears out, there's no doubt about it.
"But these sorts of structural failures are extremely significant."
Mr Richards is not alone in his concerns.
Tony Wood from the Grattan Institute said Yallourn, like all ageing power stations, was becoming less reliable and increasingly prone to problems.
He likened the plant to a person nearing the end of their life.
"The analogy of the human body is not too far off because something like 50 per cent of the money that's ever going to be spent on your health is going to be spent in the last five years or so," Mr Wood said.
"So these things tend to do the same thing."
Yallourn's owner, EnergyAustralia, said it was spending $400 million as part of efforts to keep the generator online until its scheduled retirement in 2028.
"This will improve asset reliability, safety, and performance ahead of its retirement in 2028," a spokeswoman said.
But not everyone is convinced the money will be enough.
Australian Academy of Technological Sciences and Engineering vice-president Iven Mareels said keeping old coal plants alive was "becoming very tricky".
A dean at Federation University Australia, Professor Mareels said coal-fired generators were under mounting pressure from renewable energy on two fronts.
Firstly, he said green energy sources such as wind and solar were hollowing out the business model of coal plants, meaning there was less money available for upkeep.
Secondly, he noted that coal-fired plants were still required to step in when the wind was not blowing and the sun was not shining — a practice that was taking a heavy toll on equipment and increasing the need for maintenance spending.
He said no plants were more exposed than Yallourn, where key pieces of equipment such as the boilers were being pushed to breaking point.
"That [the loss of a boiler] is basically a write-off," Professor Mareels said.
"That's a really big deal.
"Your boiler is one of the most important things you have to work with.
"If your boiler doesn't work, then nothing works."
Professor Mareels said Yallourn's problems highlighted the urgent need to build capacity that could replace retiring coal-fired generators, but worried it was not happening quickly enough.
"If you take it out too early it would cause a lot of stress on the overall grid," Professor Mareels said.
"Planning to take a generator of that size out of the system needs to be compensated for and it takes a lot of time and effort.
"For the moment, we are totally dependent on the stability being brought by all the thermal generators, because we need the synchronous machines to be able to grid-form."
EnergyAustralia acknowledged the July incident but said no-one was harmed and there was no interruption to electricity supplies.
"EnergyAustralia is committed to always prioritising the safety and wellbeing of every person who works at or visits our generation sites," the spokeswoman said.
The Grattan Institute's Mr Wood said this week's declaration of an El Niño weather pattern was likely to bring hotter and drier conditions to Australia's eastern seaboard.
He said this, in turn, was likely to heap more pressure on Australia's electricity system.
And while he said it was difficult to single out one generator such as Yallourn, he had little doubt that Australia's fleet of coal plants would be pushed to its limits.
"You can't say, 'Have I confidence in Yallourn?'," Mr Wood said.
"I have got confidence across the fleet that they will be less reliable than they have been."
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