A city graffiti removal worker found a rectangular ammunition box on a bench across from the Goodman Library and also noticed a circuit board with wiring in a nearby garbage can around 6:30 a.m., Napa police Sgt. Ryan Cole said.
The worker called Napa police, and police and the Napa County sheriff's Hazardous Device Team responded to the 1200 block of First Street, Cole said.
The bomb squad covered both objects with sandbags and detonated the military ammunition box, which measured 12 inches long and 8 inches wide, around 9:20 a.m. The circuit board was detonated around 10 a.m., Cole said.
The objects were not connected by wiring, but some small circuit boards and wiring were found inside the ammunition container after it was exploded, Cole said.
First Street was closed near Randolph Street from 6:30 a.m. to noon, Cole said.
It is not clear whether the objects posed a threat, and Napa police are continuing to investigate the incident.