Aboveground emergency vents are designed to work in conjunction with pressure vacuum vents to prevent an aboveground storage tank from becoming over pressurized in the event of a fire or blockage. When the aboveground tank reaches a determined pressure, the cast iron lid will raise up to allow the pressure to release. When the pressure releases, the cast iron cover will lower and reseat. The sturdy cast iron body and lid, along with the fluorocarbon O-ring, provide a tight seal when closed. All EBW aboveground tank vents are designed to open at 8.0 ounces of pressure.