Concern about falling debris slowing rescue of 2 trapped workers at Domtar plant in Windsor, Que.

The fear of more equipment collapsing is slowing down the process to rescue two workers who were buried under debris when a twenty-storey scaffold caved in at the Domtar pulp and paper plant in Windsor, Que., early Tuesday morning.

The workers have been trapped with no information on their condition for more than 36 hours, but rescuers still don't know how much longer it will take to find them.

What makes this rescue mission so difficult is that first responders are having to secure parts of the scaffold that didn't fall before they can continue their search inside the 60-metre-tall silo, explained the director of Sherbrooke's fire protection department Stéphane Simoneau.

His department was called to help Tuesday morning, along with the Windsor fire brigade and the plant's specialized rescue brigade.

"Our concern is to not create another collapse on the victims who are already under the rubble," he said. "We have to be careful, you understand, for the rubble, as we take out one piece at a time."

Simoneau compared the situation to dealing with a house of cards. He said accessing the area and removing the debris is hard, because entering the silo can only be done through three small access points.

And before they could even start the search, responders had to control the level of oxygen and the temperature inside the silo to make sure the victims and the rescuers would stay safe, he said.

That step is now complete, but the hardest part remains: finding the missing contractors.

"What we still don't have control of yet — and that we're trying to do — is to be able to go down as fast as possible to rescue these workers," he said. "Two lives still need to be saved and that's the mission we gave ourselves."