After posting I note safetypee's preceding post and suggest that the two be read in conjunction ...
zweifelkeks should make a phone call to the CAA to get authoritative information.
However, a quick net search provides copies of
(a) BAe ISB.21-150 which indicates applicability to the 146 series only
(b) UK CAA CAP476 and 477 which indicate that the ISB has the status of an AD
(b) UK TCDS BA 16 which relates to both the 146 and RJ and distinguish between the 146 and RJ series.
Questions arising - are there any material differences between
(a) the engine types
(b) the aircon systems
on the two series ?
I note that there are other net references which appear to indicate that some operators lump the two series together in respect to smoke and fumes crew guidance.
I'll put a link on the engineers forum and see if we can attract some Type specific knowledge to this thread.