The Patent Protected Zacon Balanced Ventilation Door and Balanced Personnel Door set the industry standard in safety.  Dividing the door into two halves, with each section swinging in opposite directions, ignores the static air pressures and ramp slopes. The force on one section opening into the air pressure and flow is cancelled by the opposite section going with the air flow. The net result is a balanced door that can be opened into extremely high pressures with relative ease.