trademark tube axial flow u201c upblast u201d belt drive fan complete with non sparking impellers and integrated butterfly dampers or equivalent the fan 60 is fitted with an appropriately classified electric motor the generator room exhaust fan 60 is preferably a start stop model which is thermostatically controlled to attempt to maintain the room temperature below a desired level eg 77 u00b0 f the exhaust fan 60 is also activated by the control system plc 62 such that the exhaust fan 60 runs for a desired period of time eg at least 5 minutes every hour for general room exhausting in addition the fan 60 may be controlled by other devices that are integrated into the system 10 a discharge pipe 64 is connected to the hydrogen generator 14 for the venting of excess oxygen and water vapour created by the hydrogen generator 14 during its operation the discharge pipe 64 extends through the inside of the ventilation plenum 50 and discharges at the roof 53 through the curb box 56 of the pre fabricated penthouse 54 the pipe 64 is sized to ensure that the hydrogen generator 14 is not exposed to a pre determined excessive back pressure eg greater than or.