One possible requirement cascade starts with FAA § 23.1309 "Equipment, systems, and installations" or its EASA equivalent; the acceptable means of compliance are usually by the adoption of a range of organisation, design and verification techniques...
The normal thermal, overheat, fire and explosion proof requirements are determined by the system integrator according to design assessment; these are the domain of standards including ARP 4761 and ARP 4754.
The resultant hardware parts specifications will include environmental test requirements; usually by the system integrator referencing selected parts of RTCA DO-160 / ED-14.
As your query context "avionics bay" and as NSEU has observed the system integrator has taken significant measures to remove combustion sustaining and explosion risk materials e.g. by the absence of fuels and hydraulic oils, even though a source of ignition is present.
My speculation is therefore that there are thermal requirements on all avionics bay electronics: -
including local assembly normal operation temperatures,
including adverse temperatures e.g. due to heat release when a local power supply "shorts",
excluding fire resistance for long duration,
excluding explosion proofness.