The company was on Tuesday convicted and will be sentenced next Friday following the deaths of Ben Pascall and Lyndon Quinlivan after the May 24 accident in 2018.

Tom Johnson was also seriously injured and was placed on life support but was released after about two weeks, and has no ongoing issues.

Details of the accident were aired for the first time in the Sydney District Court.

The court heard Mr Pascall had climbed to the top of a tank at the Ettamogah paper mill to investigate a liquid seen running down the side.

He was exposed to an unknown quantity of hydrogen sulphide gas which leaked from the top and fell unconscious.

Mr Quinlivan and Mr Johnson climbed to the top to assist the injured man and were also rendered unconscious.

Multiple employees rushed to the help the trio, including one man who climbed the ladder as other workers used an elevated work platform to take the injured men to the ground.

14 staff at the mill were told to attend Albury hospital amid concerns about possible gas exposure.

A worker who had a discussion with Mr Pascall moments before the incident, which resulted in the late man climbing onto the tank, later took his life.

In moving scenes, loved ones of the late men told of their immense loss.

Georgia Webb said every aspect of her life had been impacted by losing Mr Pascall.

She received a call to attend Albury hospital on the day of the incident and said she spent three hours in a waiting room, unaware of what happened.

Her partner had been pronounced dead soon after arriving but Ms Webb said she hadn't found out for several hours.

"It haunts me every single day having to accept my life will never be the same, that all our dreams ... were completely ripped away from us and the future and family I thought I had is gone," she said.

"My happy, exciting, driven life is now a life filled with sadness, pain and suffering.

"I used to look forward to the future, our life together, having children together and watching them grow."

Now, Ms Webb said, she was only left with memories after the unimaginable loss which could have been avoided.

"That day I lost my best friend, my partner, my soulmate and the love of my life," she said.

Mr Pascall's mother, Debrah, spoke of the torment of seeing her son's lifeless body at the hospital and leaning down to kiss him.

She had driven to the hospital unaware of his injuries, her knees buckling when she saw the area awash with emergency vehicles.

She said she still says goodnight to him before going to bed each night.

"My word has changed forever," Ms Pascall said, noting that the grief was unrelenting.

Ben's sister, Samantha, said the day of the incident plagued her dreams and had triggered night terrors and anxiety, while his other sister Eliza recalled crying in waves after receiving a phone call after his death.

Jacci Quinlivan said losing her husband and the father of her children had been "soul destroying" and she had raging anger towards the company.

She had been forced to turn off Mr Quinlivan's life support the day after the gas leak.

"It was like a horror movie," she said of receiving a call at work alerting her to the incident.

"I promised my husband whilst he was in the hospital on life support that I will get justice, accountability and I will make him proud of me and my children, and that is exactly what I will do, please make no mistake of that."

Speaking on video link in front of an photograph of her family, Ms Quinlivan asked those in court to picture her situation.

"I would like you to imagine sitting beside your life long partner and soulmate, holding his or her hand whilst they are on their deathbed," she said.

"Imagine how that would feel.

"Imagine trying to find the words to try to explain to your young children that their dad will not be coming home because he is dead.

"The thing is you can never even begin to imagine the pain our whole family is going through."

The Sydney court heard the company had failed to identify the area where the incident occurred as a confined space.

Had that been identified, steps would have be undertaken to ensure no-one would have been exposed.

The court heard the company had no knowledge, or experience, of hydrogen sulphide building up at the plant.

A lawyer for the company said it had a good safety record and apologised for those impacted by the incident.

"The company wants to say sorry," Bruce Hodgkinson said, watched on by the pair's family members.

"And it does.

"It says sorry to all of those people who have been affected."

The court heard it was hard for the company to have foreseen what happened, but steps had been taken to address the shortcomings.

Experts believe bacteria built up inside a tank storing filtrate, a type of recycled water used in the paper making process.

The incident occurred at the end of a shutdown, when operations were restarting.

The workers had been around a warm white water tank in a basement which was being filled with the filtrate.

Turbulence and the high speed of the transfer caused the liquid to change from liquid to gas and vent through several openings.

The company admitted to several failings, including not identifying the formation of hydrogen sulphide in the tank, not recognising the area was a confined space, failure to use gas monitors, and failure to provide information and training to staff about potential gas exposure at the mill.

The company should have had ventilation and exhaust systems in the area and should have monitored the filtrate during extended shutdowns.

The court heard the facts of the case were unusual.

There were no similar cases recorded by the court.

The judge thanked family members for their statements and adjourned the matter to next Friday.