When performing a Stairwell Pressurization test for the fire marshal there are a few variables to consider.  The most important of which are airflow, relief vent size, door swing/latch pressure and pressure differential along the doors.

The challenge of these variables is that every one of them affects the other.  It all starts with the airflow from the supply fan.  This gives positive pressure along the staircase which effects the swing pressure of the doors.  To reduce this pressure, an adequate area along the relief vent is necessary.  If the relief vent is too big then you would reduce the pressure differential along the doors which would fail the test.  Make sure you have proper tools to perform air diagnostic work on the supply fan, including a device to traverse the relief vent.  A calibrated manometer will also be needed to perform a DP witness test for the Fire Marshal.

The key is to have great engineering and of course some trial and error to meet all these variable within the Fire Marshals guidelines.  We at Rapid Duct Testing have 14 years of experience complying with these guidelines and are here to answer all questions.