EDMONTON -- Justin Mathews had a lifelong nut allergy and was always careful, so his family is stunned that he died after visiting a work site where walnut shells were used to blast paint off walls.

The 33-year-old was doing air quality tests at the old Rossdale fire station in Edmonton on Oct. 2, when he started having trouble breathing and went into anaphylactic shock. He suffered brain damage after going into cardiac arrest and was taken off life support five days later.

"This whole story's just insane," his sister, Joyce Mathews-Goossen, said Monday.

"My brother was there to check the air quality and the air was poisonous to him."

She said the family has more questions than answers about what happened, but hopes his death will prompt industry changes so no one else gets hurt.

Mathews had been a plumbing apprentice until he lost his job during Alberta's economic downturn, his sister said. A close friend recently gave him a job with an environmental engineering company, ESP HiTech Inc.

He had already done some work at the fire hall, vacant since the '90s and set to reopen next year. The walnut shells had been used to blast away old lead paint in the building earlier on Oct. 2, his sister said. A hopper containing the shells was still outside the building.

When Mathews-Goossen saw her brother at the hospital, his entire body was swollen. Also allergic to nuts, she was afraid to touch him in case he was contaminated.

"I still cannot believe he's gone. He's gone just like that," said their mother Mabel Mathews.

She said her basketball-loving son still lived at home. He was kind and polite, made supper when his parents were running late and was super-cautious about his allergy.

"In 33 years, he ended up in the hospital once with eating some donair with some nuts."

The family said it doesn't know if Mathews or his employer were aware that walnut shells had been used at the fire hall, if he was wearing a mask or if any warning signs were posted.

They were told Advanced Remediation Solutions did the blasting work. When asked if a manager at the company was available for comment, a man who only gave his name as Dean said staff are co-operating with provincial investigators.

He said it's not conclusive that walnut shells caused the death, since nut oils that cause allergic reactions are removed from shells during processing. And there have been no recorded allergic reactions to their decade-long use for blasting in North America.

"I don't want to take anything away from the family, but the jury's still out on this," he said.

Trent Bancarz with Alberta Occupational Health and Safety said investigators do suspect the death was caused by a severe allergic reaction to walnut shells at the fire station, although it's still early in the review.

"This is a very rare and unusual type of incident," Bancarz said. "Certainly I've never come across this before."

Silica used in sandblasting is known to cause health problems such as silicosis and lung cancer. The construction industry years ago moved to using substitutes such as walnut shells, coconut shells and corn cobs, he said.