I think from the example of the clips onto plywood, the idea is to ask 'what if the substrate is to some degree flammable?'

The key here is the premature collapse part - actually wood is not that fast to burn, even a light weight plywood door is capable of holding a fire off for several minutes, and joists and cladding actually add vital tens of minutes of rescue time.

So what is needed ?

Firstly ask can the cable fall anywhere if the clips fail ? - if it is already at floor level, or droops a bit but stays well above head height and is then trapped by other structural elements, then it is not an issue. The fact that those other elements will eventually fall sets  a cut off time, as  by then a rescue is either all over, or no longer possible.

If however long before the woodwork has burnt through, the cable has dropped to a level where it creates a lethal sticky garrote, then this is the situation to be avoided.

By far the worst are things like plastic trunking running under a ceiling, as once it softens it drops everything, leaving the screws behind.

I suspect that plastic clips nailed upwards into any substrate ,even a flammable one, are not really on as the sole means of support, as with heat from below, the plastic will always soften well before the ceiling ignites.

I think from the example of the clips onto plywood, the idea is to ask 'what if the substrate is to some degree flammable?'

The key here is the premature collapse part - actually wood is not that fast to burn, even a light weight plywood door is capable of holding a fire off for several minutes, and joists and cladding actually add vital tens of minutes of rescue time.

So what is needed ?

Firstly ask can the cable fall anywhere if the clips fail ? - if it is already at floor level, or droops a bit but stays well above head height and is then trapped by other structural elements, then it is not an issue. The fact that those other elements will eventually fall sets  a cut off time, as  by then a rescue is either all over, or no longer possible.

If however long before the woodwork has burnt through, the cable has dropped to a level where it creates a lethal sticky garrote, then this is the situation to be avoided.

By far the worst are things like plastic trunking running under a ceiling, as once it softens it drops everything, leaving the screws behind.

I suspect that plastic clips nailed upwards into any substrate ,even a flammable one, are not really on as the sole means of support, as with heat from below, the plastic will always soften well before the ceiling ignites.