I would assume long enough for people to evacuate the premises, but I have nearly run out of my Rawlplastic and the new plugs will melt, does not matter what you put the cables in, if the screw falls out of the wall, weakest link is screw in wall, so if plastic trunking has clips inside to stop cables dropping the trunking will still drop and so that is not really a help, well likely it will be worse, instead of stepping over burning trunking and cables people will have burning plastic dripped on them. I have looked at pictures of fires caused by washing machines, the kitchen was badly damaged, however all the furniture still in place, there was not enough damage for anything to fall off the walls and only plastic melted was on the washing machine, yet people died, it does not take a big fire to kill people and I do not believe in a normal house that cables will fall off the walls due to plastic melting before everyone in the house is dead. OK silly sticky back trunking yes, but if screws used to hold it no, the normal size of house will not have a problem, the only people to have a problem is the fire brigade going into the house after the fire would have killed anyone not with breathing gear, so it would need signs outside the house stating the house complied with some level of protection before they can go in. And the Liverpool car park fire highlights the time taken to get to a fire, so unless sprinklers fitted then no real point. But the problem is what is "premature collapse" if it holds the cables up long enough for people to escape then that is enough, or is it, and how long to escape, I can get down stairs in minutes when the alarm goes off, even after putting cloths on, my wife takes hours, she it seems has to have a shower first! But this is after the alarm goes off, be it mother falling out of bed, doors opening or smoke alarm until it goes off the fire has chance to get hold before anyone moves. So likely the fire will get a hold and will get very hot, when I was on the Falklands we had to get rid of excess Portakabins so they were burnt, it took 3 minutes to reduce on to ashes, by the time the forklift had picked up another cabin and taken it to the fire the one before was ashes. What is the point of tying to keep cables out of the way when the whole unit burns so fast?