Section 154.1205 - Mechanical ventilation system: Standards(a) Each exhaust type mechanical ventilation system required under § 154.1200 (a) must have ducts for vapors from the following: (3) If the vapors are lighter than air, the top of each space that personnel enter during cargo handling operations.(b) The discharge end of each duct under paragraph (a) of this section must be at least 10 m (32.8 ft.) from ventilation intakes and openings to accommodations, service, control station, and other gas-safe spaces.(c) Each ventilation system under § 154.1200 (a) and (b)(1) must change the air in that space and its adjoining trunks at least 30 times each hour.(d) Each ventilation system for a gas-safe cargo control station in the cargo area must change the air in that space at least eight times each hour.(e) A ventilation system must not recycle vapor from ventilation discharges.(f) Each mechanical ventilation system must have its operational controls outside the ventilated space.(g) No ventilation duct for a gas-dangerous space may pass through any machinery, accommodation, service, or control space, except as allowed under § 154.703 .(h) Each electric motor that drives a ventilation fan must not be within the ducts for any space that may contain flammable cargo vapors.(i) Ventilation impellers and the housing in way of those impellers on a flammable cargo carrier must meet one of the following: (1) The impeller, housing, or both made of non-metallic material that does not generate static electricity.(2) The impeller and housing made of non-ferrous material.(3) The impeller and housing made of austenitic stainless steel.(4) The impeller and housing made of ferrous material with at least 13mm (0.512 in.) tip clearance.(j) No ventilation fan may have any combination of fixed or rotating components made of an aluminum or magnesium alloy and ferrous fixed or rotating components.(k) Each ventilation intake and exhaust must have a protective metal screen of not more than 13mm (0.512 in.) square mesh.