... 3,Oil, Acid, Alkai & high temperature Resistantflexible duct:/air duct/exhaust duct,ventilating duct,flex duct, ventilation duct 1 ... engineering,fire-fighting to ventilate or exhaust waste air,dust to supply fresh air.keep more savely and effectively during working. ... engineering,fire-fighting to ventilate or exhaust waste air,dust to supply fresh air.keep more savely and effectively during working. ...