Key Points:

    • Ride malfunctioned three times on fatal day
    • 2001 warning: 'I shudder to think if there'd been a guest on the ride'
    • Operators told not to use emergency stop button
    • The code engineers used to describe malfunction revealed

A Dreamworld ride operator was unsure which emergency button to press to prevent the Thunder River Rapids ride tragedy, an inquest has heard.

The principal police investigator has told a packed Southport Coroners Court the main control panel for the ride was confusing and the operator had previously been deterred from using an immediate shutdown button.

On the opening day of the inquest into the October 25, 2016, tragedy that killed four people, including former Kawerau woman Cindy Low, the court also heard of a history of malfunctions on the Thunder River Rapids.

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Detective Sergeant Nicola Brown said the water pump on the ride at the Gold Coast theme park stopped working twice in the hours before the fatal accident.

Brown said no engineering staff attended the second time, and that it was simply reset.

Less than an hour later, the pump stopped working a third time, resulting in the water level near the unloading point of the ride to drop so rafts were no longer buoyant but were sitting on maintenance rails.

A raft carrying six guests collided with an empty raft that was stuck on the rails, raising both into a vertical position.

Kate Goodchild, Luke Dorsett and Roozbeh Araghi and Cindy Low died when they were thrown onto the conveyor belt mechanism. Goodchild's 12-year-old daughter and Low's 10-year-old son survived, despite also being thrown out of the raft.

Dreamworld staff's safety fears

The inquest was also told that if the two-second emergency stop button at the end of the ride had been pressed at any time before the rafts collided, the tragedy could have been avoided.

An explosive first day of the inquest revealed staff were told not to use an emergency stop button and the ride had malfunctioned three times on the fatal day.

"The button must only be pressed in the event the main control panel cannot be reached," the memo read.

The button could stop the conveyor belt in less than two seconds, whereas the main control panel would stop the conveyor belt in seven seconds.

The tragedy unfolded when a raft became stuck on the conveyor belt 57 seconds before the fatal accident. The raft the four were travelling in hit the stuck raft and flipped them onto the conveyor belt.

Brown told the inquest the ride operator who was near the only emergency stop button did not know what it was for.

She said the operator was told: "Don't worry about that button, no one uses it."

The ride operator was not aware the button could stop the conveyor belt in two seconds.

Brown said the main control panel was also "confusing" and it was not clear which button stopped the ride immediately.

The control panel only had a "slow stop" of the conveyor belt.