The workers were on the back side of the Capitol Terrace Apartments just before 10 a.m. when things went wrong.
Witness Tim Tuttle said the equipment "somehow turned on itself," breaking a window and leaving the two workers dangling above the street.
"So the thing obviously went katawonk," Tuttle said.
Olympia firefighters arrived on scene moments later and found the men hanging from their safety lines. One of the men was bleeding from the head.
"His head was bleeding -- it bled a lot, so it was very dramatic looking," Tuttle said,
Firefighters moved their articulated ladder truck into the narrow alley behind the building and extended the ladder up to the workers. Crews then helped both men down to safety.
"We were scrapping the bushes on both sides as we came up here. I don't believe we would have ever gotten our old ladder truck up here to pull off the rescue in the same way," said Deputy Olympia Fire Chief Gregory Wright.
The injured worker was taken to a local hospital for treatment. The second washer wasn't hurt.