Residents of an evacuated 21-storey tower in downtown Vancouver could be locked out for several more days after potentially dangerous chemicals were released inside the building.

Trouble at the Electra Building began on Friday after a urethane foam product that was being used to raise the buildings concrete floor had an unexpected chemical reaction. Fire and Rescue personnel evacuated the building for a few hours before determining the fumes coming from the foam were not harmful.

Fire and Hazmat teams returned on Saturday, however, forcing a second evacuation as they reassessed the toxicity of the fumes.

On Sunday, residents were told that the City of Vancouver Environmental Protection Officer would not lift the evacuation until the entire building was surveyed by an industrial hygienist.

The hygienist must determine whether residents' belongings, including blankets, curtains and clothing, were contaminated by the fumes. The building's strata council will meet with consultants on Monday morning to get an estimate of how long the survey will take to complete.

Residents have also been informed that the strata's insurance does not cover their personal costs, including relocation expenses, loss of revenue or any other costs.

Battalion Chief Gary Sarai of Vancouver Fire and Rescue said residents could be locked out until mid-week. "They gotta check every room so it could be a couple days," he said.

Firefighters entered the building on Saturday night to retrieve residents' medication, keys, wallets and pets, Sarai said.

Two people were treated for chemical exposure on Friday, but no other injuries have been reported.

The foam was being used to raise the buildings concrete floor.

Witnesses said fumes began filling the building with an "overpowering solvent-like stench" on Friday afternoon that progressively grew worse over the course of the day.

Smoke eventually started billowing out of the building into the street. "It looked like it was a really foggy day," Ed Lee, who works in the building, told CTV News. "That's obviously when we all started becoming really concerned."

Authorities have blocked sections of Nelson and Hornby streets three days in a row, causing traffic disruption in the area.

WorkSafe B.C. will be investigating the incident.