NEW YORK (CBSNewYork) — The FDNY on Tuesday released the cause of a Harlem fire that killed a firefighter on a movie set in March.

Fire marshals say the heat from a boiler ventilation flue ignited combustible materials in the cellar of 773 Saint Nicholas Ave.

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The building’s sprinkler system was also shut off, according to officials.

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Firefighter Michael Davidson died while fighting the flames. He was posthumously promoted to lieutenant.

The New York Police and Fire Widows’ and Children’s Benefit Fund has promised to provide financial support for Davidson’s family. To learn more about the fund or to donate, click here.

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The Stephen Siller Tunnel to Towers Foundation has also pledged $100,000 to help pay off the family’s mortgage. To learn more about the foundation or to donate, click here.