When a local ventilation system is required by the regulations of the United States Department of Labor, such ventilation system shall comply with the following requirements:
- The discharge point of the ventilation system shall be at least 25 feet (7620 mm) from pedestrian traffic, building openings or sources of ignition. Prevailing wind direction and location of adjacent buildings shall be considered in selecting the discharge point.
- At each discharge location there shall be a durable sign, conspicuously posted, that reads "DANGER—FLAMMABLE GAS."
- Signage shall appear on the duct at intervals of not more than 20 feet (6090 mm) and at least once in each room and each story traversed by the duct. Such signage shall be by means of metal tags, stenciling, stamping or adhesive markers, which shall be attached or imprinted in a manner that is not readily removable.
- A sparkproof centrifugal fan with backward curved blades designed for continuous operation shall be used, and the impeller and the ring around the impeller drive shaft shall be nonferrous.