Power plants don't just explode. There are a whole host of entities that could be responsible in this case, and the responsible thing to do is gather all the evidence, all the information, all the data at the accident scene."

Sheff represents the families of Mark Mansfield, 41, of Peabody and Phillip Robinson, 56, of Beverly, who died after the Nov. 6 accident along with Mathew Indeglia, 20, of Townsend.

The attorney for Indeglia's family, Neil Sugarman, worked with Sheff on Thursday night to get the restraining order from Middlesex Superior Court Judge Bonnie H. McLeod-Mancuso.

Investigators for Essex District Attor ney Jonathan Blodgett had been planning as soon as yesterday to cut boiler pipes near the explosion location to send them to a lab, according to court filings.

But McLeod-Mancuso ordered Blodgett's office and plant owner Dominion Energy New England Inc. not to remove or destroy any gear in or around the explosion site until the families' lawyers can "inspect and document the premises."

"Such items may be valuable evidence in a potential third-party wrongful-death lawsuit," the judge added in her ruling.

The three workers were scalded with high-pressure steam estimated to be up to 600 degrees when the pipe exploded, spewing asbestos and dust, as they were performing routine maintenance.

Among the questions investigators are asking is whether a crack in the boiler line could have led to the explosion.

Jim Norville, Dominion spokesman, said the company had no comment on the restraining order but did not expect the move would delay the return to normal operations at the plant.

"There's not a whole lot in the area affected by the incident that we can do until the asbestos cleanup plans are approved," but environmental regulators haven't approved them yet, Norville said.

Salem Harbor comprises four generating units, three fueled by coal and a fourth by fuel oil, that produce steam to run electric turbines that can collectively generate 955 megawatts of electricity, enough to power about 715,000 homes.

Officials say that all four units remain closed.

Because of quirks in the design of the New England power grid, Salem Harbor is often crucial - particularly in the summer - to maintaining reliable electricity in communities north of Boston.

It is not known when the 55-year-old plant will resume operations. "It's way too early to even talk about restarting" the power plant, Norville said.

Asked whether the court move could snarl the investigation, Stephen O'Connell, Blodgett spokesman, said, "We expect the injunction will temporarily delay cleanup efforts and the recovery of evidence, but ultimately it won't change what the evidence is."