The natural gas pressure surge that led to dozens of home explosions last week in Massachusetts very likely damaged the system's antiquated network of pipes and could require lengthy testing and repair before service is restored to thousands of customers.

That means people and businesses in three towns may be waiting weeks or months for household basics like hot water, heat and cooking.

An apparent malfunction sent gas through the pipelines at 12 times the normal pressure last Thursday, perhaps more in places, according to data released by lawmakers and investigators. Much of the system is made of cast iron, which is brittle and can crack under pressure, said Richard Kuprewicz, a consultant who specializes in pipelines.

As a result, NiSource Inc.'s Columbia Gas of Massachusetts must test the scores of supply lines to at least the 8,600 customers before gas can be switched back on, a painstaking process, Kuprewicz said. "It takes a while to do this," he said. "Meanwhile, the winter is coming."

While people living in the region were allowed to return home on Sunday and electrical power was restored, NiSource hasn't said when it expects to get its gas supply system working again. "We are not currently turning gas service back on for customers on the affected system in the area," Columbia said on a website for customers. "Our first priority is to ensure the safety of the public and the community. We do expect this to be an extended restoration process."

Of the 8,600 customers affected, some won't see service returned until pipes in their neighborhoods are replaced, said Ken Stammen, a NiSource spokesman.

Gas could be restored for others before a full replacement, he said. It's "impossible" to know how many customers fall into each category and the timetable for restoration hasn't been determined, he said.

Replacing gas pipelines typically takes years, but the company said it's accelerating its plans to replace the pipelines.

An additional 5,800 customers who live outside the core areas had their gas shut off as a precaution, Stammen said. Service has been restored to most of them.