A mail carrier, a clerk and a customer exited the building around 11:10 a.m. after their eyes, ears, noses and throats became irritated and they began coughing, Vallejo Fire Department firefighter and paramedic Arthur Gonzales said this afternoon.
As a precaution, the fire department closed two blocks in each direction around the post office and issued a shelter-in-place order, Gonzales said.
The three people with symptoms were treated at the scene, Gonzales said.
"This is a static incident. There was no release, spill or open package," Gonzales said.
The Solano County Environmental Health Services Division's hazardous materials response team arrived around 2 p.m. and is searching the building for the source of the irritant, Gonzales said.