Emergency responders were dispatched to the scene, a noodle cafe in the 400 block of Broadway East, at about 12:15 p.m. after a call came in about the accident.
The woman was still conscious and alert when medics arrived, the Seattle Fire Department said in a tweet.
A technical rescue team had to use specialized tools to free the woman's arm, which had been pierced by a metal shaft. She was then taken to Harborview Medical Center.
It was the second day in a row that someone's arm had become entangled in industrial equipment at a Seattle workplace.
On Thursday, a 55-year-old man lost his arm in an industrial accident at a fortune cookie factory in Seattle's International District, officials said.