40 years on, the government apologises for Australia's most deadly rail disaster.

“I want to take this opportunity, 40 years on from that sad and horrific day, to acknowledge and apologise on behalf of the State Government to all those who still suffer today as a consequence of what happened.”

These were the words of NSW Premier Gladys Berejiklian earlier today as she fronted those directly affected by the 1977 Granville Train disaster in Western Sydney. Family members of victims were in attendance, so too were the first respondents and hospital staff.

Today is the first time the State Government has apologised for the disaster that claimed the lives of 83 people and should never have happened.

Early on the morning of January 18, 1977 a crowded eight-carriage train left Mount Victoria in the Blue Mountains. The morning commuters were on board, travelling to work in Sydney’s city.

Two hours later, at 8:10am, the train was approaching Granville railway station when the first carriage left the rails.

It collided with a row of pillars, weakening the support of the Bold Street bridge above. The pillars were made of steel and concrete and the first carriage splintered on impact disconnecting from the train. Eight people were killed instantly.

The rest of the train ground to a halt, with second carriage stopping just clear of the overpass. This meant the third and fourth carriages were directly beneath the bridge when it collapsed. It was a string of devastating events all caused by poor trackwork.

“There are tragic days in history which have a lasting impact on our collective memory,” Premier Berejiklian said today.

“We very rarely see them coming but the way we choose to respond to them have a profound and lasting effect on victims that have loved ones and the community more broadly. 18th January 1977 was such a day.”

570 tonnes of steel and concrete, plus the cars crossing the bridge at that time, fell onto the carriages below.

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Half of the passengers died instantly. These were the ‘lucky’ ones. The rest were trapped.

Many stayed alive for hours after the accident, while medical crew and emergency services struggled to deal with the horror.

It’s the stories of these passengers, the ones trapped by an arm or a leg, that are the most chilling.

In many instances, they were lucid and talking with the emergency staff. They would have been thinking of their families, maybe even feeling grateful that they were still breathing while so many lay dead beside them.

But they didn’t know about crush syndrome — a condition emergency services weren’t equipped to deal with either.

It’s a cruel physiological phenomena that occurs when the pressure of the crush is lifted and the person is ‘freed’. This freedom is false.

Soon after the release, a toxic cocktail of muscle breakdown products leave the site of injury and flood the blood stream. They hit the kidneys and the body goes into shock. Soon after, the 'freed' patient will die.

"Unfortunately the support that many first responders should have received at that time, they did not receive, and we are deeply sorry about that," the Premier said.

"You carry the pain and the scars, but you've also taught us many of the lessons that we have since applied in the last 40 years."

Ultimately 83 people died and another 213 were injured on the morning of January 18, 1977.

Today, those closest to the incident - who lost family members or were there to hold the hands of those dying - finally received an acknowledgement from the people responsible for the tragedy: the NSW Government.