Firefighters have not determined cause of massive San Francisco fire that damaged six buildings

An investigation on Wednesday in San Francisco continued into a massive fire that tore through several commercial buildings.

Fire Lt. Jonathan Baxter said that despite it being 24 hours later, the fire was still not fully contained because of the smoke still permeating the scene. Three engines and three trucks remained on "fire watch" to oversee the hot spots. 

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The cause of the five-alarm blaze remains under investigation, Baxter said, despite the fact that there was a mattress fire that erupted at a homeless encampment hours before the Tuesday flames broke out. A task force will remain on scene.

"This process is very scientific and detail-oriented," Baxter said, but to definitively link the two would be premature at this point. 

The five-alarm fire that damaged six buildings broke out Tuesday at 6:30 a.m. near the Central Freeway at 14th Street between South Van Ness and Folsom in the inner Mission District.

Firefighters also acknowledged that they were there hours before that on Monday at 11:30 p.m. when they were called to extinguish a mattress fire the night before on Erie Street, on the backside of Bartfeld Sales, a business that sells steel fabricated building supplies.

Baxter said when crews left, that mattress fire appeared to be out. 

'The whole building is gone:' 75-year-old family business destroyed in 5-alarm San Francisco fire

Tuesday morning's fire created huge plumes of black smoke could be seen while more than 100 firefighters battled the flames.

One witness who had to evacuate said it smelled like burning tires.

"The flames were three times as high as the building was it was fully engulfed back there," said Scott Perkins. 

Baxter said when firefighters first arrived, "you could not see your hand in front of your face" and there was a lot of falling debris. 

Two buildings were destroyed and four were damaged including a sheriff's building. Baxter said that crews were able to help salvage a glass company that was affected. 

One firefighter was injured and had to be transported to the hospital. Baxter said that he was now "resting comfortably" and is appreciative of the community's support.