... tunnel, basement, ship building or welding, laboratory ,air-conditioner. flexible duct:/air duct/exhaust duct,ventilating duct,flex duct1,Material: PVC flam-resistant static-free ... as tunnel, basement, ship building or welding, laboratory ,air-conditioner,engine room, the municipal conduct engineering,fire-fighting ... portable ventilator to use together. high temperature flexible duct with metal ring