Cargo is not really my thing, but in my mind wouldnt it be a lot more practical /cheaper/effective to make sure that potentially combustible cargo is not loaded on the aircraft in the first place?
A big part of the utility of cargo operations is that we carry nearly anything nearly anywhere...including a wide variety of hazardous materials. Hazmat classifications place quite a few types of materials as "cargo aircraft only."
You're suggesting that a major economic industry shut down because what's carried is hazardous...when that's largely why that industry exists; cargo aircraft carry hazmat.