Two people were in critical condition and two firefighters suffered minor injuries in this house fire Feb. 10 on Capitol Hill. (Courtesy of D.C. fire)

A fire in a home on Capitol Hill early Friday that left two occupants critically injured, including a professor at the University of the District of Columbia, began in a basement furnace, investigators have determined.

A university spokesman confirmed that the professor, John L. Slack, 75, was injured in the fire. He is the director of the school’s public health program, serves on the executive board of the UDC Faculty Association and has authored several books.

The fire was first reported about 5 a.m. in Slack’s two-story home in the 700 block of Maryland Avenue NE, two blocks from Stanton Park. Fire officials said that one of the occupants tried to put out the fire with a bucket of water, but flames quickly spread throughout the home and to the roof.

A spokesman for the D.C. Fire and Emergency Medical Services department said firefighters found a man, later identified as Slack, on the lawn outside the home. A police report said he suffered severe burns to most of his body.

Another male occupant was found in the basement, authorities said, and he too was hospitalized in critical condition. Fire officials had initially identified that person as a woman. The police report says a third occupant, a woman who said she was watching television in the living room and smelled smoke, escaped unharmed.

Nancy Erickson, who lives across the street, said she heard shouting from other residents and then saw the man outside.

[Elderly woman seriously injured in fire in Southeast Washington]

Erickson said firefighters arrived quickly and confronted flames shooting out the front door. “It was incredible to watch their bravery,” the neighbor said. Two firefighters suffered minor injuries.

Amy Offner, who lives on Maryland Avenue, said she knew Slack from being a neighbor. She described him as a “good man with a big heart.” Janet Durig runs the Capitol Hill Pregnancy Center next door to Slack. She described Slack’s occupants as a longtime border and a handyman. Of Slack, she said, ‘He was a very interesting man, a very bright man.”

Slack’s relatives did not return calls on Friday.

Friday’s fire on Capitol Hill came just two days after firefighters in Southeast Washington rescued a 95-year-old woman from her first-floor apartment that caught fire from food left on a stove. The woman was seriously injured.

Fire officials said on Friday that a smoke detector alerted the elderly resident and her neighbors to the fire. The officials said they have not determined whether the Maryland Avenue house had a smoke detector as well.

On Friday afternoon, representatives of Pepco Holdings donated 1,500 smoke detectors to the D.C. fire department’s smoke-detector giveaway program. District residents can call 311 to arrange a smoke detector installed for free.

Firefighters on Friday revisited the neighborhoods of both fires to check whether homes have smoke detectors and to install them where needed.