Phil L wrote:
The wall is 'sealed' from any sources of fire (plasterboard is a good fire
proofing) and the fibreglass/rockwool will never melt and give off toxic
fumes if something does ever happen.

Is there some confusion here? Rockwool and fibreglass can actually be
used for fire protection. The stuff's inert, and can't give off toxic
fumes. Are you thinking of expanded polystyrene?