A moving car, quick-thinking bystanders and a whole lot of grace helped a San Francisco window washer survive an 11-story fall, witnesses said.

The window washer, whose name was not released, fell screaming from the roof of a downtown building. He landed with a crash onto a moving sedan, a Toyota Camry driven by Mohammad Alcozai.

The window washer stayed on the car for a moment, then rolled onto the pavement, bleeding, breathing hard, but conscious, police and witnesses said.

More than a dozen people, including the car’s driver, a retired Army colonel and a nurse, came to the man’s rescue. They called 911 and in the frantic minutes before an ambulance arrived, detoured traffic and covered the man with clothes and tried to comfort him.

Alcozai jumped out of his car as soon as the man landed on it. The roof collapsed and the car was totaled, but Alcozai walked away unscathed.

Alcozai calls it a “miracle” that he and the window washer survived. He told The Chronicle that he was meant to be there when the accident happened. He said he was supposed to go on a call Friday morning, but it was canceled, so he went downtown. He said he was making a left turn when his car’s navigation system went blank, so he slowed down.

As the system turned back on, he sped up — “and that’s when something hit my car with a terrible thump,” he told the newspaper.

The window washer remains in San Francisco General Hospital with life-threatening injuries. Cal/OSHA spokeswoman Julia Bernstein said the man suffered a broken arm and injuries to his side, KGO reported.

The man was moving equipment on the roof of a bank building in the heart of San Francisco’s financial district and not on a window-washing platform when he fell, San Francisco police Sgt. Danielle Newman said, according to the Associated Press. The platform was on the ground at the side of the building, and cables were hanging from its sides. It was not clear whether the man was setting the platform up, but he was working with a partner, police said.

The man may have slipped as he was adjusting the cables of this rig, KGO reported. He apparently had not clipped himself onto the safety line.

The man worked for Concord, Calif.-based Century Window Cleaning, said Peter Melton, a spokesman for the California state division of occupational safety and health.

The company was cited for one serious violation and three other violations in 2008, one of them related to instructing window-cleaning employees in the proper use of all equipment provided to them, and supervising the use of the equipment and safety devices to insure that safe working practices are observed, according to federal records. The company was fined more than $6,500, though the fine was eventually reduced to a little more than $2,700.