Skip to Main Content

This information is provided free of charge by the Department of Industrial Relations from its web site at These regulations are for the convenience of the user and no representation or warranty is made that the information is current or accurate. See full disclaimer at
Subchapter 7. General Industry Safety Orders
Group 16. Control of Hazardous Substances
Article 107. Dusts, Fumes, Mists, Vapors and Gases

Return to index
New query

§5143. General Requirements of Mechanical Ventilation Systems.

(a) Design and Operation. The construction, installation, inspection, testing, and maintenance of exhaust systems shall conform to all requirements of Article 107. Additional guidance may be obtained from the American National Standard Fundamentals Governing the Design and Operation of Local Exhaust Systems, ANSI Z9.2-1971 and the Standard for the Installation of Blower and Exhaust Systems, NFPA No. 91-1973. Note:Ventilation requirements for control of flammable vapors are prescribed in Sections 5153(d) and 5416.
(1) The exhaust system shall be so designed, constructed, maintained and operated as to prevent harmful exposure by maintaining a volume and velocity of exhaust air sufficient to gather dusts, fumes, mists, vapors or gases from said equipment or process and to convey them to suitable points of safe disposal, thereby preventing their dispersion in harmful quantities into the atmosphere of work rooms or other places where persons are employed.
(2) Exhaust ducts, inlet ducts, and fan plenums shall be so designed, constructed, and supported as to prevent collapse of the ducts and/or failure of the supporting system.
(3) Exhaust ducts which convey dusts, fumes, and mists shall be provided with inspection or clean-out doors at intervals not to exceed 12 feet of horizontal running length for ducts up to 12 inches in diameter, but the distance may be greater for larger ducts. A clean-out door or doors shall be provided for servicing the fan and, where necessary, a drain shall be provided.
(4) Two or more operations shall not be connected to the same exhaust system where the combination of substances removed may constitute a fire, explosion, or chemical reaction hazard in the duct system.
(5) The ventilation rate of every mechanical ventilation system used to prevent harmful exposure shall be tested after initial installation, alterations, or maintenance, and at least annually, by means of a pitot traverse of the exhaust duct or equivalent measurements. Records of these tests shall be retained for at least five years.
(b) Duration of Operations. The exhaust system shall be in operation continually during all operations for which it is designed. The system shall continue to operate for some time after the cessation of said operations, the length of time to depend upon the individual circumstances and effectiveness of the ventilation system.
(c) Disposal of Exhaust Materials.
(1) The air outlet from every dust separator/collector and the dusts, fumes, mists, vapors or gases collected by an exhaust or ventilating system shall discharge to the outside atmosphere, provided that the exhaust system shall discharge to the outer air in such a manner that it will not
cause a harmful exposure in any accessible workplace. Collecting systems which return air to work areas may be used if contaminants which accumulate in the work area do not result in harmful exposure to employees.
(2) The air exhausted from blast-cleaning equipment, grinding, buffing, polishing equipment and all other equipment requiring exhausting of dust or particulate shall be discharged through dust-collecting equipment. Dust and refuse discharged from an exhaust system shall be disposed of in such a manner that it will not result in harmful exposure to employees.
(d) Make-Up Air. Clean, fresh air, free of contamination from adjacent industrial exhaust systems, chimneys, stacks, or vents, shall be supplied.
(1) The outside air supply shall enter the workroom in a manner which will not reduce the effectiveness of any local exhaust systems.
(2) All seams and joints shall be sealed if negative pressure exists within inlet ductwork such that there is a possibility of infiltration of harmful quantities of gases, fumes, or mists from areas through which ductwork passes.
(3) Where the air supply is filtered, the filters shall be replaced or cleaned regularly to prevent significant reductions in airflow. A pressure gauge shall be installed to show the pressure drop across the filters. This gauge shall be marked to show the pressure drop at which filters require cleaning or replacement.
(4) Where make-up air is heated by combustion, except gas, the products of combustion shall not be mixed with the make-up air and shall be vented to a point remote from all points where make-up air enters the building. For gas heating where combustion products are mixed with the make-up air, the following must exist:
(A) The gas must be nontoxic and have a distinctive and strong enough odor to warn workmen of its presence if unburned.
(B) The maximum rate of gas supply to the make-up air heater shall not yield in excess of 2000 ppm of total combustible gas in the mixture upon flame failure.
(C) A fan shall be provided to remove the mixture of heated air and combustion products from gas burner plenum chambers. (Title 24, T8-5143)
Note: Authority cited: Section 142.3, Labor Code. Reference: Section 142.3, Labor Code.
1. Amendment filed 7-16-76; effective thirtieth day thereafter (Register 76, No. 29).
2. Amendment of subsection (a)(2) filed 2-20-80; effective thirtieth day thereafter (Register 80, No. 8).
3. Editorial correction of subsection (a)(5) (Register 2003, No. 24).

Go BackGo Back to Article 107 Table of Contents