Abstract: A pressure relief panel assembly for protecting a building against over-pressure caused by explosion. The assembly has a panel pivotally connected to a frame and held by a calibrated magnet and striker set which releases when a predetermined over-pressure occurs. A cable restraint attached to a shock absorber, or a linkage of two arms attached to a shock absorber, limits the extent to which the panel can blow open. A spring mounted on one of the arms catches the other arm when the panel has blown open, preventing the panels from reclosing and thereby preventing implosion damage to the building. Alternatively, or additionally, the panel, after opening, may be held partly open by a stop bar which pivots to prevent the panel from fully closing, to prevent implosion damage to the building after the explosion.