Also Friday, officials from the state Department of Labor announced they're investigating a total of 10 companies who had employees at the plant when the explosion took place. Three ConAgra employees were killed and dozens of workers were injured in the explosion June 9.
Investigators from the U.S. Chemical Safety Board suspect that contract workers venting a natural gas line into an interior pump room released vapors that led to the explosion. The release of natural gas came as a cluster of contract workers cleaned a 3-inch-diameter gas line during the installation of a commercial water heater at the plant.
Lawyers for the firm of White & Stradley say the companies added to the lawsuit Friday were involved in installing the water heater.
"I would characterize it as more than human error," said David Stradley, a lawyer representing four injured workers who have filed a civil lawsuit in Johnston County Superior Court. "I'd characterize it as human recklessness."
Added to the lawsuit were Energy Systems Analysts and the Jacobs Engineering Group. Also named as defendants were an employee from each company, who attorneys allege were overseeing work at the plant.
Stradley said Energy Systems Analysts, a Hickory-based firm, manufactured and helped install the water heater. He said Jacobs Engineering, which has a local office in Cary, drew the plans for installing the water heater and supervised the work.
Stradley alleged that neither firm is licensed in this state to work with gas lines.
Representatives could not be reached from either firm on Friday.
The lawsuit also has been amended to include additional allegations of negligence against the firm originally named in the complaint, Southern Industrial Constructors, a contract firm that received permits to install the water heater. Southern Industrial has denied its workers are to blame.
State Department of Labor spokesman Neal O'Briant says inspectors are looking at all the companies, including an industrial water heater-maker and a mechanical contractor.
The Chemical Safety Board, an independent federal agency, hopes to wrap up its investigation in Garner in the coming weeks and will return to sites in Washington and Colorado to try to reconstruct the blast. It could be nine to 12 months before that board releases a final report.
The Associated Press contributed to this report.
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