Firefighters initially responded to the first fire, just north of South 188th Street, at about 11:30 p.m. Sunday.
Two northbound lanes of the freeway were closed for hours during overnight firefighting efforts, and an eight-mile backup had formed in the northbound lanes by 7 a.m. Monday. One lane was reopened by 9 a.m., and the backup had shrunk to about two miles by 11:45 a.m. All lanes were reopened by early afternoon.
Then at around 11:40 a.m. Monday a second brush fire broke out along the southbound lanes of I-5 south of the Fife curves near 70th Street.
Two lanes were closed and a backup began to form there as well as crews responded to the scene and thick clouds of smoke poured over the freeway. That fire was extinguished by 12:20 p.m. and lanes were reopened.
Investigators looking into the cause of the overnight fire said it may have been started by flames from a car's exhaust.
Capt. Kyle Ohasi of the Kent Fire Department said several people reported seeing a car on the shoulder of the freeway with fire coming out of the tail pipe just before the blaze started.
As the fire grew, flames shot 30 feet into the air and spread across about three acres as drivers watched firefighters try and knock them down. By 6:30 a.m. Monday, crews were still dousing hot spots.
No structures were threatened. Eventually units from Tukwila, SeaTac, Federal Way, Port of Seattle and Boeing Fire Department assisted in the firefight, with approximately 40 firefighters.
Fire officials are using the opportunity to remind drivers that extreme fire conditions currently exist, not just in Central and Eastern Washington, but in the greater Seattle area and all of Western Washington.