1998 sect I pg-58.3.2- date of revision or interpretation

[davefitz]

Can anyone advise the code case or interpretation that led to the revision of sect I pg-58.3.2? In particular, I need to obtain the date of effect of the wording change - prior to about 1998, that paragraph required boilers installed on a header system to use one "non-return valve" plus one stop valve on the steam connection to the header. After about 1998, the wording chagned to require 2 stop valves plus a bleed.