A partially obstructed flue pipe in the boiler system caused a carbon monoxide leak in a building at Roanoke College early Saturday.

Seven people were in the Sigma Chi fraternity house at the time of the leak, but no one was injured, said Teresa Gereaux, director of public relations for Roanoke College. Saturday's incident came just two months after a carbon monoxide leak in the college's Sections dorm building killed a man and sent scores of people to the hospital.

About 1 a.m. Saturday, a resident of the fraternity house contacted campus safety officials when the carbon monoxide alarm went off in the house, and campus officials evacuated the house.

When the Salem firefighters arrived, they determined that carbon monoxide had leaked into the house, in amounts as high as 400 parts per million in some places, said Lt. John Prillaman, of the Salem Fire Department.

At that level, an hour of exposure can cause headaches, and prolonged exposure can cause death, Prillaman said.

Fire personnel spent more than an hour ventilating the building by using fans to get the carbon monoxide readings back to zero.

By Saturday evening, residents had begun to return to the house.

The college installed carbon monoxide alarms in all of its buildings following a July 14 leak caused by a mechanical breakdown in a gas water-heater that claimed the life of 91-year-old Lutheran pastor Walter J. Vierling, of Pearisburg and sent 62 others to the hospital.

"We are determined to keep our campus safe, and it is reassuring to know that the safety measures we implemented this summer are working," said Sabine O'Hara, president of the college, in a news release. "This incident is also a reminder that all of us need to take it seriously when we hear an alarm sounding on campus. The residents of the house immediately contacted Campus Safety, and I am grateful for their quick and appropriate response."