Explosion vent apparatus is provided, which includes a vent support unit defining a vent opening adapted to be aligned with an area to be protected from an overpressure condition, a vent panel movably mounted on the support unit in a normal closed position blocking the outlet and movable through a first displacement away from its closed position to a first overpressure-relieving position upon application of an overpressure of one magnitude of pressure while allowing movement of the vent panel through a second and greater displacement to a second overpressure-relieving position upon application of a higher overpressure. The vent panel does not deform or rupture upon opening, and recloses after pressure relief, either under spring pressure when opened under a lower first pressure, or by a fluid actuated reclosing mechanism upon full opening of the vent panel under a higher second pressure.