MA – By Dorian Block and Raja Mishra, Boston Globe |

Authorities cut off gas service to nearly 1,800 homes and businesses yesterday as they scrambled to control natural gas leaks that fire officials said triggered a violent explosion, leveling a Civil War-era house.

Rescue workers determined that gas lines in the town had been dangerously over-pressurized, a condition that nearly led to explosions in seven other houses. Lexington Fire Chief William Middlemiss said late last night officials were closing in on a cause of the explosion — and believed they had fixed the problem — but declined to say anything more.

The situation stabilized last night, with gas service off and Keyspan and fire crews conducting a house-by-house search for leaks that was expected to stretch well into today. Still, hundreds of people left town, unwilling to weather the night without heat.

”This will be going on all night long and into [Thursday], and that’s a best-case scenario,” Middlemiss said. He offered a warning: ”If someone smells something in their home, they should not pick up the telephone. Do not turn on the lights. Go out the nearest door.”

A Keyspan spokeswoman said each house would have to be inspected twice before gas service could be restored. The company sent out 110 crews to investigate all 1,800 homes and businesses. By 11 p.m. yesterday, Keyspan had checked about half the homes and had found no further problems. The company could begin turning gas back on, house by house, by 8 a.m. today.

”The cause of the incident is still under investigation,” said the spokeswoman, Carmen Fields. ”Keyspan is cooperating with all appropriate public safety and regulatory officials. We will check the homes for safety and any drifting gases or leakages.”

The day’s chaos began at 11:19 a.m. at 3 Hancock Ave., where Thomas Thrasher, 29, was inside when a loud bang startled him, as his mother was outside.

”He hears something pop,” Middlemiss said. ”He went downstairs, smelled gas, and left the house. They were fortunate to get out.”

The house, built in 1865, exploded moments later, causing a blaze that took more than two hours to extinguish. The boom resonated at the high school a mile away, frightened bikers on the Minuteman Trail, and jarred area businesses.

”I thought someone had driven a car into the side of our building,” said Frank Yunes, who was working in a nearby office building.

Antra Thrasher, 64, Thomas’s mother, was working in the yard, neighbors said. They said they saw her face covered with blood and her hair singed as an ambulance took her away. All that remained was a knee-high pile of charred rubble and a single wall from the rear of the house.

Around 1:30 p.m. yesterday, with the fire under control, it seemed as if life in Lexington would return to normal. Then reports of gas odors surfaced at one house, then another, then many more. Firefighters and Keyspan crews rushed to investigate, finding that seven houses had near-explosive levels of gas pressure, Middlemiss said. The ratio of gas pressure to oxygen in the natural gas lines feeding the houses had grown dangerously unbalanced, he explained.

The Lexington Fire Department declared the situation unstable and ordered Keyspan to shut down gas service to a broad cross-section of the town. There was confusion about whether those residents would have to evacuate. But it turned out they did not.

But with many residents leaving to avoid heatless homes, traffic in Lexington was at a standstill on major arteries. The Red Cross opened a shelter at Lexington High School, but by late last night no one had planned on staying there. Police checkpoints appeared at major intersections. Many restaurants in Lexington Center closed early yesterday, unable to make much food without gas ovens or heat.