Formula needed for vent size of atmospheric tank

[Sparky1949]

NFPA 30 22.7.4* states "Extension of Emergency Vent Piping. Piping to or from approved emergency vent devices for atmospheric and low-pressure tanks shall be sized to provide emergency vent flows that limit the back pressure to less than the maximum pressure permitted by the design of the tank."

Where can the formula to calculate the pipe sizes be found?

If the answer is the "Hazen-Williams" or "Darcy-Weisbach" equations, how does one allow for air as the medium?

 

[Sparky1949]

Never mind, it is the "Darcy-Weisbach" equation.

 

[IFRs]

Just curious - what equation did you use and what was the result?

 

[psafety]

The Darcy equation as shown in Crane TP410.