Third-shift workers walked out of Boeing’s giant factories at Renton and Everett, Washington, as their contract expired early Friday morning, blasting music and airhorns, shooting off fireworks, and waving hand-made signs. They immediately formed picket lines and began setting up homemade burn barrels with “IAM” carved in the side. “People are really excited to strike,” said Ky Carlson, a third-shift assembler who walked out at midnight and was picketing the Everett plant at 3 am.