Pacific Structures has been the subject of six Cal/OSHA investigations over the past five years. It was cited only once.
Cal/OSHA officials believe crews hired by Emerald Steel were the ones conducting welding work before the fire.
Representatives from both companies have not returned calls for comment.
A three-alarm fire at an old hotel under renovation near San Francisco's Civic Center on Monday has prompted investigations by two city agencies and the state's workplace safety regulator.
Those probes come five months after a massive blaze destroyed a large apartment project in the Mission Bay neighborhood. After that fire city officials issued warnings to construction crews throughout San Francisco to obey safety rules. In fact, the battle over who is to blame in that much larger blaze recently intensified.
On Monday afternoon it took firefighters almost three hours to get control of the fire at the site of the former Renoir Hotel at 45 McAllister St. The fire, which was reported at 12:03 p.m., sent smoke billowing into the air from the eight-story structure and affected traffic on nearby Market Street.
Fire officials said eight workers were injured, seven of them hospitalized with smoke inhalation. The injuries prompted the state's Division of Occupational Safety and Health to investigate the work site, Cal/OSHA officials said.
The San Francisco Fire Department has also launched an investigation. Despite reports that the fire might have started from welding on the second floor of the building, SFFD spokeswoman Mindy Talmadge said, "I have not heard any possible causes yet."
Fire Chief Joanne Hayes-White called the director of the city's Department of Building Inspection, Tom Hui, the agency's top official, according to DBI spokesman Bill Strawn. Hui, a licensed structural engineer, went to the site of the fire that afternoon along with building inspector Tam Chiu, Strawn said.
The San Francisco Chronicle reported on plans for a $30 million renovation of the shuttered Renoir Hotel:
The renovation of the Renoir Hotel is considered a centerpiece of the revitalization of the Mid-Market neighborhood. The project is being built by the Kor Group, which made its mark in New York and Los Angeles with the trendy Viceroy hotels.
The new Renoir, which has not yet been named, will include a 4,500-square-foot roof deck bar and lounge. In addition, the Kor Group is planning three restaurants and bars on the ground floor.
Monday's fire occurred almost five months after a massive blaze destroyed a large condominium project under construction in the city's Mission Bay neighborhood. Fire officials have said the March 11 fire was accidental but may have been caused by sparks from welding or grinding.
The fire department issued a $1,000 citation to a subcontractor on that project on Fourth and China Basin streets, near AT&T Park. Investigators said the firm's workers failed to keep a required "fire watch" in the area where they had been welding and grinding before the blaze.
That company, Petaluma-based T.C. Steel, appealed the citation in June, saying the fire department's findings arose from confusion or mistranslation when a Cantonese-speaking welder was interviewed by investigators the day after the fire that caused $40 million in damage.