The Madison Fire Department responded to a gas leak on Williamson Street late Tuesday morning, evacuating  buildings on the 1200 block for about two hours, Fire Department spokesperson Eric Dahl said.

Crews from Madison Gas and Electric were already on the scene when the fire truck arrived, according to a statement from the fire department.

Dahl said the incident occurred after someone working in the building accidently cut the natural gas pipe.

Firefighters used a public address system from their fire truck evacuate people from the building, the statement said. Firefighters could not safely enter the building to aid in the evacuation due to the explosive atmosphere the gas created, according to the statement.

“The natural gas is explosive depending on the concentration,” Dahl said. “If there is any spark or open flame in the building that can ignite the gas and cause an explosion.”

The statement said MGE crews and firefighters used fans to ventilate the building free of the gas.

Dahl said crews blocked off about four blocks to vehicles and foot traffic, which were reopened at about 1:30 p.m. when gas meters reached safer levels.