At least 35 employees were taken to the hospital after they were overcome by a food preservative at a Southern California trucking business, officials said.
More than 40 firefighters, including from hazardous materials crews, responded to Swift Transportation, 11888 Mission Blvd. in Mira Loma just before 8 p.m., Riverside County fire officials said.
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Two workers were on a forklift trying to load something onto a truck when they were exposed to unknown chemicals, fire officials said. The exposure then spread to some 30 employees.
At least 35 employees were taken to hospitals by ambulances and MTA buses.
Authorities said the unknown substance was determined to be sodium benzoate, which turns into an irritant when mixed with moisture.
Cal/OSHA was expected to investigate. Further details were not immediately available.
Beverly White contributed to this report.