A 78-year-old man who was killed in a fire over the weekend in a Near West Side high-rise building was smoking while on oxygen.

About 11:20 p.m. Saturday, firefighters responded to the blaze on the 11th floor of the 21-story building in the 300 block of South Damen, according to Fire Media Affairs.

“Upon confirmation of the fire in that unit on the 11th floor, we escalated to a 2-11 alarm due to the number of occupants in the building at this time of day and due to the smoke conditions on the 11th floor,” Chicago Fire District Chief Jerry Knapp told reporters at the scene.

Amos Lewis, 78, was found in that unit and was taken to Stroger Hospital, where he was pronounced dead a few minutes after midnight on Sunday, according to fire officials and the Cook County medical examiner’s office.

Lewis, who lived in the building, was on oxygen at the time of the fire. An autopsy Wednesday found he died of inhalation injuries and careless use of smoking materials. Heart disease as listed as a contributing factor, and his death was ruled an accident.

The blaze was contained to one apartment on the 11th floor, but other tenants on the 11th floor were displaced when their units were rendered uninhabitable, fire officials said. No one else was injured.

The city’s Department of Human Services was called to the scene to assist with housing.