Twenty-nine employees of a Jurupa Valley trucking company were overcome Friday evening by fumes of an unknown substance, according to the Riverside County Fire Department.
Hazardous materials crews responded to reports of a noxious odor in a trailer at Swift Transportation on Mission Boulevard at 7:47 p.m., according to the department.
Ambulances took 19 employees to a hospital, and the remaining 10 were to be sent via bus.
The cause of the incident was under investigation. County environmental health agents and firefighters from the city of Corona were assisting.