So you're not keen on it then Kurnal?
Thanks for the frank response. It's pretty much what I thought. Unfortunately the system design has proceeded without my involvement and I now find myself as "the bad guy" becasue I'm querying it. It seems to have had "approval" from BC, though the letter giving this supposed approval is vague in the extreme and recommends "a fire engineer" be involved in justiyfing the system, which seems to me like a nice get out for BC.
Now I am querying the whole basis of the so-called solution, the designers are saying that as it was "bespoke" it's not to the BS but if we want it to be designed to the BS (EN 12485 or BS 8489), it would be much more difficult to do and we're now talking about tanks and pumps and goodness knows what else, none of which there is space for. Well, yes. That's why I (and a previous assessor) suggested re-instating the structural protection in the first place! The suggested system is water mist by the way, which seems like clever technolocy and I admit I have little experience of it personally, but I don't see how it removes smoke from a smoke-logged staircase...
To return to a second to BS 9999. As I undersatand it, you may reduce the risk profile if you have sprinklers or water mist fitted. That allows you to use a different figure for the maximum allowable travel distance. It's not going to allow you to have a travel distance of 45m with only one means of escape, though in any circumstance. The only way to do this is re-instate the structural protection I believe.
I did also do some reading on this and found some articles about use of sprinklers / water mist in domestic situations and whether they could replace structural protection and the consensus seemed to be - not really. Mainly this seems to be becasue the escape route could become smoke logged before the suppression system activated and then even when it did activate it would not clear the smoke.
I can see this one is going to be interesting, as the designer continues to insist that the system in some magic way can be considered to "protect" the staircase and so travel distances magically shirink to 18m on each floor into the so-called protected area! I have pointed out that "protected" in BS 9999 is defined as "with fire resisting structure" but it's falling on deaf ears. Oh well, I can't say I haven't tried!