The Oregon Department of Environmental Quality found asbestos at the blast site after natural gas sparked an explosion on Northwest 23rd Avenue this week.
Spokesman Matthew Van Sickle said tests done Thursday morning discovered asbestos among the rubble of a 110-year-old building. Roofing felt was found that contained 35 percent of the dangerous fibrous material.
The department will be spraying foam on the debris and monitoring air quality on a daily basis, but there is no public safety concern at the site, Van Sickle said. However, as a precaution, officials are extending the closed-off area to the public, he said.
Fire Bureau investigators have been advised of the asbestos discovery, Van Sickle said. Investigators will continue with their analysis of the rubble as they work to determine the ignition source of the blast.
"We have an abatement contractor that will begin work as soon as they are allowed to," Van Sickle said.