It may not have been a faulty boiler after all that sent 50 people to hospital with carbon monoxide poisoning over the weekend.

An investigation into what caused the mass poisoning at the Ice Box Arena on Saturday could be concluded as early as today and the arena reopened by this afternoon, said its manager Dawn Couture.

"We're hoping so," she said Monday afternoon. "I'm basically putting everything from tonight's ice time to tomorrow, and we'll wait and see what can be cleared between tonight and tomorrow afternoon."

Fortis B.C. initially suspected a faulty boiler, sending a technician to turn off the main valve over the weekend and attaching a red tag, which prevents anyone but a licensed gas fitter from fixing the problem.

But speculation is now leaning towards the propane-powered ice-resurfacing machine made by Olympia, said Couture.

"I can't confirm anything," she said. "There's not a definite answer, but probably."

Mechanics were seen working on the ice-cleaning machine Monday, but arena staff wouldn't discuss precisely what the problem was.

The facility's owners, B.C. Safety Authority and WorkSafeBC were investigating the arena Monday.

WorkSafe B.C. is overseeing the investigation since a worker was also poisoned in the incident. By Monday afternoon, the cause was not determined, said communication officer Megan Johnston, but the machine is being looked at.

The arena cannot be opened without WorkSafeBC's approval, said Johnston.

"There would have to be no imminent danger to a worker," she said. "As long as they were in compliance tomorrow, yes, they would be able to open up."

The B.C. Safety Authority regulates such technologies as gas, boilers and electrical. Spokesperson Kelly Haddon said technicians are being very diligent in their investigation but the problem may not be in the authority's jurisdiction.

"We're starting to think it's possible none of the B.C. Safety Authority regulated technologies are actually involved in the incident," Haddon said Monday.

Royal Inland Hospital went to orange alert Saturday afternoon when dozens of people arrived after the arena air was filled with as much as 200 parts per million of carbon monoxide. Several more trickled in and three patients were kept overnight. All were released by Sunday.

Arena owner Gary Hartnell could not be reached for comment but Couture said sympathies were with the 50 poisoning victims.

"Of course we're just happy that they're all doing well now and we're just investigating the issues here."