zdas04,
Sorry for any confusion. The ASHRAE is not completely clear, but the section referenced is telling the user what the minimum capacity (required capacity)of a relief device must be for the different types of refrigerant based on vessel size. This is not an uncommon approach to sizing...
I would suggest checking out ASHRAE 15 Section 9.7.5(American Society of Heating, Refrigerating and Air-Conditioning Engineers - Saftey Standard for Refrigeration Systems)
Below is an excerpt, but I'd suggest getting a copy of the standard and reading through it.
9.7.5 The minimum required...