Dear all!

I have a question regarding the applicability of CII relief load synthesizer.
In B31.1 AII-II-1.2 it is said that a system is open only if the discharge to the vent pipe through an umbrella fitting or directly to atmosphere has got a very reduced length (l<4D, m<6D).
Nevertheless I read in CII Technical Reference 5.92 that CII relief load synthesizer that this tool is valid for open type vent systems and it seems to refer only that the exit is to the atmosphere, saying nothing about any maximum length of vent pipe in systems with no umbrella fitting.
I mean, the definition of open system for CII is the same that for B31.1? Is there any limitation in vent pipe length of a system discharging to atmosphere with no umbrella fitting when using CII relief loads tool?

Thnak you