Flood protection for underground air vents

Apparatus for allowing ventilation through a ventilation shaft to an underground ventilation duct fluidly communicating through the ventilation shaft to an atmospheric opening of the shaft and on threat of flooding operable to prevent downward flow of surface water into the underground ventilation duct, comprising

• a support comprising opposed lateral sidewalls for arrangement in said shaft defining a passage between top and bottom openings of the support for fluid communication of said ventilation duct up through said support to said atmospheric opening,
• one or more panels having proximal and distal ends, a top side, and a bottom side, said proximal end connecting with a horizontal hinge having a hinge axis perpendicular to said opposed lateral sidewalls for rotation of said one or more panels upwardly to an upright home position not obstructing said passage and rotation from said home position downwardly by gravitational impetus of the weight of such panel to reach a lower passage closing position, said one or more panels having a profile that closes said passage when said one or more panels gravitationally rotates to said passage closing position,
• a suspension member unobstructively horizontally spanning said passage supported on said opposed lateral sidewalls proximate said top opening and holding said one or more hinge connected panels in said passage proximate said bottom opening,
• a panel handle on said top side of said one of more panels for manually rotationally raising said one or more the panels from said passage closing position toward said home position, and
• a lift arm for each of said one or more panels, each lift arm having a proximal end and a distal end, said proximal end being pivotally connected by a pivot pin to said bottom side of said one or more panels on a pivotation axis parallel to said hinge axis, each said lift arm being of dimension to contact said distal end with one of said opposed lateral sidewalls when said distal end is pivoted upward inside said sidewall for exertion of lateral force onto the connected panel to which the lift arm is connected and that is being raised with said handle of said one or more panels, thereby to complete rotation of that panel into said home position.