I do not know aboyut the left coast code BUT here is a quote from one of the codes I use.
FIRE SAFETY AND HEALTH ISSUES.
RS 13.3 SYSTEM COMPONENTS 301(d) 4:No pipes,conduits or structual members shall pass through the walls of these ducts.
hope this helps Next time ask on our list as the P&H folks here have no clue to real codes.
Read off the WALLFrauds postings for example