San Francisco — The back of a dump truck delivering 20 tons of dirt to businesses on Sixth Street in San Francisco tipped and crashed into an adult video arcade this week, narrowly missing three patrons.

“It was close,” said a video clerk at the Liberty Bookstore, who identified himself as Jersey Dog. “One guy was near the inside of the wall, but no one was hurt.”

The incident happened at 9:10 a.m. when Sukhdev Singh of Economy Trucking was dumping dirt to be used to fill in several businesses’ sub-basements on the 100 block of Sixth Street, said Sheri Costa, a spokeswoman for the city Department of Public Works.

The back of the truck tipped over to the side and into the wall of the store, shattering windows and dumping dirt into the part of the store that houses booths for video peep shows.

Firefighters used a thermal imager to ensure that no one had been buried dead or alive under the mound of dirt. Then they closed off the area and waited for a building inspector to deem the building structurally sound.

Traffic on the stretch of Sixth south of Mission Street was only slightly affected, mainly by motorists leaning out their windows to snap pictures with their camera phones.

Police Sgt. Jim Millett said he didn’t know who would have to pay for the damage. But, he said, “there are liability issues here for sure.”

Both the Department of Public Works and the city Redevelopment Agency are trying to improve the blighted stretch of Sixth Street by putting in street lights, new sewers and sidewalks. But first, the local businesses have agreed to pay some of the cost of bringing their sub-basements up to code.

No one could explain the upending of the back of the truck, but driver Singh blamed the road, which he said was uneven.

This is the second accident in as many years to damage adult stores at the corner of Sixth and Mission streets.

On Dec. 15, 2003, a 14-Mission bus slammed into the Golden Gate Adult Superstore across the street from the Liberty Bookstore. Seventeen people were hurt in that accident.