DALLAS (AP) — A Dallas school where high carbon monoxide levels prompted an evacuation has canceled classes for a second day amid safety concerns.

The Dallas Independent School District says Lakewood Elementary would not be in session Wednesday.

Carbon monoxide levels were acceptable when checked in classrooms Wednesday morning, but remnants were present once a boiler was started.

The more than 800 students and the staff were evacuated Tuesday morning when a contractor noticed high levels of carbon monoxide. The problem was traced to a furnace in the basement.

Authorities later discovered a deal owl was clogging the ventilation system. The carcass was removed.

A district statement says crews will work Wednesday to make sure that Lakewood Elementary School is clear.