SAN FRANCISCO (CBS SF) — San Francisco fire officials said Monday that TC Steel of Petaluma was the subcontractor whose work is believed to have started the large blaze at a construction site in the city’s Mission Bay neighborhood in March.

Fire officials said TC Steel’s president, Tom Cleary, has been cited and fined $1,000 for being out of compliance with the city’s fire code.

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The company was doing hot work welding at the construction site at 1200 4th Street, according to fire officials.

The massive five-alarm blaze, which destroyed a 172-unit, six-floor residential complex at 1200 4th St., was reported shortly before 5 p.m. on March 11.

San Francisco fire officials said in a recent report that the fire was accidental and occurred after “an event involving a wire welding unit or grinder between the top floor and the ‘high roof’ area.”

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The report said the fire caused $40 million in property damage.

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The structure was part of a larger project known as MB360 that was being developed by BRE Properties of San Francisco. The work was being done by Boston-based Suffolk Construction with the assistance of many subcontractors,

Cleary and other TC Steel officials couldn’t immediately be reached for comment Monday night.

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