Text in force at 23-63: from 23-62, effective 31 Jan 2012.
For all airplanes with engine(s) embedded in the fuselage or in pylons on the aft fuselage the following applies:
(a) No material in any fire extinguishing system may react chemically with any extinguishing agent so as to create a hazard.
(b) Each system component in an engine compartment must be fireproof. -
76 FR 75760 · Source