SAN FRANCISCO (KCBS)- San Francisco fire officials say an early morning fire near the city's Castro neighborhood Monday was not arson as previously suspected.

The fire broke out shortly after 3 a.m. at a two-unit residential building at 390 and 392 Corbett Ave. and spread to a home at 1370 Clayton St., according to the fire department.

That's near the area where four suspicious fires burned last week. But San Francisco fire spokeswoman Lt. Mindy Talmadge said investigators now say this fire was caused by painting materials lying outside on the deck.

"Based on all of the evidence that they found, they were able to make a quick determination that the cause of the fire was the result of spontaneous combustion," said Talmadge.

The fire was spotted by a patrol passing through the area in the wake of the suspected arson cases last week.

Sixty-four firefighters responded and had the blaze under control by 4:11 a.m., an acting fire lieutenant said.

Residents were evacuated safely and no injuries were reported. The American Red Cross was called to help the victims, who were all adults.

At least six people were evacuated from the home, but no one was hurt. One apartment was heavily damaged, and another had smoke damage.

Monday morning's fire caused about $405,000 in damage to the two buildings, according to preliminary estimates from the fire department. 

Meanwhile Talmadge said the investigation into last week's suspicious fires continues.

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