The three-alarm blaze burned for more than two hours as PG&E crews struggled to cut off the flow of gas at the site. The fire gutted a restaurant, damaged several other buildings and prompted investigations by the National Transportation Safety Board, the California Public Utilities Commission, California's Division of Occupational Safety and Health and the San Francisco Fire Department.

On Tuesday, Supervisors Catherine Stefani and Sandra Lee Fewer called for a hearing to review the incident and asked that representatives of several agencies speak before the Board of Supervisors.

"We want to ensure that contractors conducting work on our streets maintain the highest standards and meet all safety requirements at the federal, state and local level," Stefani said before the board.

Part of the investigations into the explosion will be aimed at determining the plans and delegation of work for the fiber optic installation that spanned six blocks of Geary between Parker Avenue and Emerson Street.

The project involved several companies in four states. Telecommunications giant Verizon applied for and received a permit from the city for the installation. Verizon then hired MasTec, a Florida infrastructure engineering firm, as its main contractor.

MasTec, in turn, contracted with Advanced Fiber Works, which hired a recently created San Francisco company — Kilford Engineering — for part of the construction.

In a statement, Advanced Fiber Works disputed the idea that it was doing physical work on the project.

"The work being performed at the job-site had been subcontracted to Kilford Engineering, a state- and city-licensed contractor with many years of experience in underground cable installation. AFW had no employees on site at the time of the incident nor was it performing any physical work associated with the project. At no point was AFW responsible for assigning or providing employees to the job site," the statement said.

Joshua Weiner, a representative for Advanced Fiber Works, said the project was the first the two firms had worked together.

Weiner did not answer repeated questions about what actual work AFW was tasked with on the project.

An employee for Kilford Engineering was driving the excavator that struck the underground natural gas pipeline that ruptured, according to Frank Polizzi, a spokesman for Cal/OSHA.

Polizzi said Kilford was hired to dig a trench, install conduit and seal up the excavation. AFW was supposed to eventually snake cables through the conduit, he said.

Cal/OSHA is currently investigating Kilford Engineering in connection with the explosion — not the other firms involved in the work, Polizzi said.

Kilford Engineering, which obtained its state business and contractors licenses late last year, issued a statement through a communications firm in Cleveland, Ohio.

"It is important to note that no cause of the fire has been established and any speculation to the contrary undermines the integrity of this investigation, which must be given time to reveal answers as to what occurred," the statement said.

Lopes, the spokesman for the contractors board, said if AFW was involved in physically installing communication lines, the contractor would be in violation of state regulations requiring a C-7 license to do the work.

Verizon has not answered questions about the incident since it issued a statement hours after the explosion.

A representative for MasTec has not answered questions about the role AFW played on the project.

So far, NTSB investigators have focused on PG&E's actions. Last Friday, officials with the federal agency said they were trying to find out how long it took PG&E to shut off the gas after the line was broken. Federal investigators planned to secure several feet of the ruptured pipeline and possibly send it to a lab for more analysis.

A PG&E spokeswoman declined to name the contractor that contacted the utility to determine where gas lines were in the area. PG&E has said that it marked the location of the lines before work began.

Eric Weiss, a spokesman for the NTSB, said the agency expects to release a preliminary report on the case in the coming days.