SAN FRANCISCO (CBS SF) — Muni is inspecting hundreds of buses and trolleys after two caught fire last week, the agency said.

The fires happened on two separate buses.  600 volts of electricity burned through the connectors, starting the fires.

“We had a fire on the pole that connects the trolley pole to the top of the overhead wire,” John Haley of the Municipal Transit Agency said.

No one was hurt, but Muni isn’t taking any chances with the aging fleet.

“They are all 15-years-old. They’ve been in service for that long. They have approximately 500,000 miles on each of them,” Haley said.

The buses are supposed to last 15 years.  They should be retired, but Muni can’t afford to replace them all.

“We’ve got a whole bunch on order, but of course it’s going to take a while to get them of course,” Haley said.

The trolleys are limping into retirement, as mechanics work to ensure they are still safe.

“Well, we have a lot of mechanics that presumably keep them in pretty good shape, and we haven’t had a whole lot of problems with them. But, they are right at the end, that’s for sure,” Municipal Transit Agency Chair Tom Nolan said.