The carbon monoxide that killed an elderly man and sickened more than 100 teens and adults staying in a Roanoke College dormitory last week had leaked from a natural gas-powered water heating system, investigators said Wednesday.

Pressure built up in a basement mechanical room of the dormitory over about a 24-hour period, forcing the carbon monoxide into the rest of the building through cracks and crevices, said Pat Counts, chief of the Salem Fire-EMS Department.

The system is supposed to shut down if one of its many pieces fails, he said.

The Rev. Walter J. Vierling, 91, was found dead Friday morning when emergency officials responded to calls that people staying in the dorms for two summer programs were suffering from nausea, dizziness, headaches and shakiness.

In all, 114 people were taken to two Roanoke Valley hospitals. Most were attending a Lutheran conference. Others were teenagers staying in the dorm as part of a summer college preparatory program.

A five-member task force formed to study carbon monoxide safety on campus met for the first time Tuesday.