B.C. labour advocates are calling for a coroner's inquest into the release of toxic fumes at a mushroom farm that killed three men and left two more with permanent brain injuries.

The three deceased workers were overcome by fumes at a Langley farm in September 2008. Another two tried to rescue them; Michael Phan remained in a coma for almost three years and has suffered serious brain damage, while the other lost his hearing and ability to speak.

On the third anniversary of the catastrophe, the BC Labour Federation says that an inquest is necessary to determine what exactly went wrong.

"Those three people didn't need to die and two didn't need to be seriously injured," federation President Jim Sinclair told reporters Tuesday.

"We're looking for a situation that says these people were not horribly injured or killed for no reason -- that something will change."

Investigators have said that on the day of the disaster, a pipe carrying a compost mixture broke, releasing the fumes.

The operators currently face no criminal charges in connection with the incident, and were instead charged under the Workers Compensation Act and Occupational Health and Safety Regulations. They face a maximum fine of $600,000 and up to six months in jail.

Ha Quan Truong, Van Thi Truong, Thinh Huu Doan and two companies, A-1 Mushroom Substratum Ltd. and H.V. Truong Ltd., entered surprise guilty pleas to 10 of 29 charges in May and are set to be sentenced this month.

Sinclair says he wants to see jail time for those responsible.

"We would have liked to have seen criminal charges laid, let us be very clear," he said.

"We are seeking the stiffest possible jail terms under the code, that's six months for each charge, so that the judge can send a clear message to employers and British Columbians that this kind of atrocity is not acceptable business practice."

Tracey Phan, the teenaged daughter of injured man Michael Phan, said her life has been forever changed by what happened on the farm.

"Three years ago my dad was able to sit and talk to us, he was able to joke around with us.... Now I can't get any words out of him," she said.

"I don't know how things are ever going to be the same again for my family. I know that my mom has it really hard. She is a single parent now."