The fires, one Wednesday afternoon and one Monday night, both started in an expansion joint in the eastbound lanes of Interstate Highway 80 just east of Treasure Island, according to the California Highway Patrol.
A fire coming from beneath the bridge and up through the expansion joint into the roadway was first reported on Monday around 10 p.m. near the Treasure Island exit. The fire, quickly extinguished, blocked two lanes of traffic for around an hour.
A second fire was spotted just after noon on Wednesday, with lanes reopening around 1:50 p.m.
Caltrans spokeswoman Leah Robinson-Leach said the fires damaged the rubber seal on the joint, which protects it from debris and saltwater, and repairs will be needed. However, the damage has not created any safety hazards for drivers. "The bridge is always in view and so that has a lot to do with why these fires were put out within minutes of being reported," Leah-Robinson said.
A bridge engineer discovered Wednesday's fire and called CHP and the San Francisco Fire Department who put out the fire within minutes.
Robinson-Leach said Monday night's fire burned about six feet of the seal and the second fire burned about half of that.
The bridge seal will need to be replaced. "We will not speculate on the cause until we are very clear as to what the cause of both fires is in fact," Leah-Robinson said.
Caltrans has not yet determined when repairs on the seal and joint will take place, she said.
No one was injured in either fire.
Bay City News contributed to this story.
Photos from today's Bay Bridge fire. CHP and Caltrans on scene investigating. pic.twitter.com/nNZcPmUIwA— CHP San Francisco (@CHPSanFrancisco) July 15, 2015