Both men had safety harnesses when one of the booms attached to the 16 story building at 300 Berry Street failed. One of the men was pulled to the roof by firefighters. The second man was brought in through one of the windows of the building.
"When I took a couple of steps out, I saw two gentlemen out on the scaffolding, one hanging from the platform, one about the middle of the platform. Obviously it was a little frightening being so close," said witness Augi Yi.
"I was hoping and praying that the other end wouldn't collapse. Because the only thing that held it up was that arm on the roof and if that goes, he goes," said witness Rodney Blanchard.
Cal/OSHA is investigating why the scaffolding collapsed.
The men were taken to San Francisco General Hospital with serious to moderate injuries.