Four former Dreamworld workers are suing the Gold Coast theme park, two years after they witnessed the horror of four people dying on the Thunder River Rapids ride.

Three of the four workers will give evidence at the inquest into the October 2016 incident, that took the lives of Roozi Araghi, Kate Goodchild, Luke Dorsett and Kiwi Cindy Low.

Represented by Shine Lawyers, the four first responders say they are still psychologically damaged from trying to help the four people pinned.

Shine Lawyers' solicitor Tina Ibraheem told news.com.au the four first responders' "level of trauma is beyond anything I have ever seen".

The four who died - Roozi Araghi, Kate Goodchild, Luke Dorsett and Kiwi Cindy Low. Photo / Supplied

Shine Lawyers is representing safety officers Shane Green, John Clark and Rebecca Ramsey and engineer Paul Burke who have all left Dreamworld and are all involved in ongoing counselling.

The three safety officers were part of Dreamworld's medical team and were called as soon as the ride flipped, crushing the four victims between the wooden conveyor belt and the raft.

"Nobody should ever have to see what they were confronted with when they entered that trench," Ms Ibraheem said.

"The victims' bodies were so badly disfigured from crush and compression injuries that these first aid officers were completely helpless, there was nothing they could do.

"The nation was overcome with grief and everybody tried to piece together in their minds what happened to those innocent people as they were dragged into that machinery.

"Our clients, however, saw exactly what happened to the four bodies and they have to live with those images for the rest of their lives."

Three of the four first responders will take the stand to testify at the inquest into the Dreamworld tragedy — something that's played heavily on their minds Ms Ibraheem said.

"The lead-up to this week has been incredibly distressing, it's a date that has played on their minds for nearly two years," she said.

"One of the hardest memories for our clients to forget is the screams of the victims' family members who were right there wanting them to do more to save their loved ones. They so desperately wanted to do more, but the victims were gone."

The second two-week block of the Dreamworld inquest started yesterday.

Senior police officers arrive at the scene of the accident at Dreamworld. Photo / News Corp

The details of an earlier collision between empty rafts on a Dreamworld ride on which four people would die in 2016 are set to be revealed at an inquest into the fatal incident.

Stephen Buss was operating the Thunder River Rapids ride in 2014 when two rafts collided in similar fashion to the incident.

Mr Buss was subsequently fired following an internal investigation by the Gold Coast theme park.

Yesterday, the court heard an employee admit Dreamworld had suffered a "total failure" to identify safety issues on the ill-fated Thunder River Rapids ride.

Maintenance planner Grant Naumann conceded issues such as pinch points had been overlooked with the 30-year-old ride before a malfunction in October 2016 led to the deaths of four visitors.

Counsel assisting Ken Fleming QC asked Mr Naumann if there had been a "total failure by everybody" to identify risks with the ride.

"In hindsight, yes," Mr Naumann replied after a long pause.

The fatal incident occurred after a water pump failed, dropping water levels and leaving a raft stranded on a conveyor belt.

Operators failed to shut down the conveyor belt before the raft containing the four victims collided with it, forcing both rafts to flip and the visitors to suffer fatal injuries in the ride's machinery.

Mr Naumann had earlier said he believed some maintenance operations may have been deferred for budgetary reasons.

But he said he had never been told explicitly he could not attend to safety issues due to monetary factors.

The scene at Dreamworld after the disaster. Photo / News Corp

The inquest also heard an emergency stop button on the main control panel of the ride was never checked by a maintenance supervisor.

"That button was not a part of our pre-operational checks," maintenance supervisor Stephen Murphy said.

Mr Murphy also revealed senior management had altered a policy to allow a ride to break down three times in 24 hours before it was shut down.

"It was passed down from the management meeting that we would do it that way," Mr Murphy said, adding he didn't know when the order to extend it from two break downs in one day had been made, or why.