Napa Fire put out a debris fire Sunday morning inside an underground chamber beneath the Maxwell bridge on Imola Avenue.
The blaze occurred in a Caltrans bunker that had been occupied by homeless people, said Fire Capt. Laurel Chamness.
The fire required the response of two engines, with firefighters donning breathing apparatus to climb down into the chamber, Chamness said. They used an extinguisher to put out the blaze, which emitted a column of smoke, she said.
This was the second fire in this vault in recent weeks. The department put out another debris fire on March 29.
People are breaking off a door lock to gain access to the chamber, Chamness. Caltrans is working on a plan to strengthen the lock, she said.
No one was in the chamber when the fire department responded at 9:30 a.m. Sunday, Chamness said.