California Code, Labor Code - LAB § 2353

In any factory, workshop, or other establishment where dust, filaments, or injurious gases are produced or generated, which may be inhaled by employees, the person, under whose authority the work is carried on, shall cause to be provided and used, exhaust fans or blowers with pipes and hoods extending therefrom to each machine, contrivance or apparatus by which dust, filaments or injurious gases are produced or generated.  The fans and blowers, and the pipes and hoods, shall be properly fitted and adjusted, and of power and dimensions sufficient to prevent the dust, filaments, or injurious gases from escaping into the atmosphere of any room where employees are at work.