About 20 people were taken to hospitals Friday complaining of respiratory problems after being exposed to chlorine gas at an industrial dry-cleaning facility, officials said.
Sulfuric acid and bleach were mixed together, causing a gas cloud inside the building, said Vista Fire Department inspector Adrian Abel.
Chlorine gas is an irritant that poses an inhalation hazard.
Fifty employees of Prudential Overall Supply were evacuated from the building. All employees were accounted for, and search crews found no one inside the building, Abel said.
The gas cloud was contained inside the facility and did not spread to neighboring buildings, Abel said.
Firefighters and sheriff's deputies responded shortly after 8 a.m., said San Diego County sheriff's Lt. William Donohue.
No information was immediately available regarding the condition of those injured.
Investigators from the state Occupation Safety and Health Administration were expected to begin an investigtion, Abel said.
Vista is about 40 miles north of San Diego.
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