San Francisco firefighters were unable to locate the source of the substance that caused respiratory irritation in 34 people and triggered the evacuation of the building at 1 S. Van Ness Ave. at 3:07 p.m., fire department spokeswoman Mindy Talmadge said.
The building, which houses San Francisco Municipal Transportation Agency's headquarters and other city offices, was evacuated after occupants began reporting coughing and breathing problems, Talmadge said.
Fire officials identified 34 people who showed symptoms of being exposed to a mild respiratory irritant, but no one was hospitalized, Talmadge said.
One woman, Sylvie Elliott, was turning in paperwork for a residential parking permit at the SFMTA office when she said she felt a burning in her throat. She said it was hard to breathe and felt like there was pepper irritating her throat.
Elliott was evaluated in the back of an ambulance parked outside the building and afterward, she was told to wait near several ambulances on Market Street near South Van Ness Avenue while wearing a gray blanket.
Firefighters and hazardous materials teams searched the building several times for the source of the irritant but could not locate or identify it, Talmadge said.
Building occupants were allowed to go back inside around 4:15 p.m., Talmadge said.
The high-rise holds a large number of people and the evacuation produced a large crowd on the street, with most huddled on the west side of South Van Ness Avenue in front of a Honda car dealership.
Police tape blocked off South Van Ness between Market and Mission streets, and nearby sidewalks were also cordoned off.