RTI's

[GB]

Can anyone guide me with accepted / approximate figures for RTI's for domestic mains wired smoke detectors.

[wee brian]

Last time I needed this I was using FPE tool - it had standard values in it that were OK.

This is years ago though

[kurnal]

I'm interested in another angle on this one- this time for systems incorporating a system to 5839 say L1.
In an assembly building of traditional construction, assuming good management contol of risk and procedures, in which capacity is limited by means of escape rather than area, is there any general consensus on the benefits of replacing a type M system with an L1 system in order to  increase capacity- earlier detection of fire leads to more time for safe evacuation and less risk of panic?  We could do some sums but I am interested in opinions and gut reaction.

I think the biggest weakness in such a scheme would be for the sudden conflagration, arson attack or similar.

[wee brian]

It depends really. AFD is only an added benefit if people would not have found the fire by some other means - ie seeing it in front of them.

The next issue is that if you have narrow exits the queing increases. queing in a large crowd is not nice and can be unsafe.

[Chris Houston]

It depends really. AFD is only an added benefit if people would not have found the fire by some other means - ie seeing it in front of them.

There might be a small time saving if the detection system raised an alarm before people were able to realise the danger, react correctly and get to a call point.

[wee brian]

yes  -if they other people cant see the fire themselves.

If you are in an auditorium and the fire is in front of you an alarm is just a noise.

If the fire is elsewhere in the building then AFD will be helpful.

Kurnal is talking about increasing the occupant capacity of an assembly building - I doubt AFD is the right answer.

[kurnal]

Thanks Guys
You are both bang on.
I have in mind a small, multi occ  listed building of two floors with an assembly hall on the first floor with capacity by floor area  for up to 240 persons,  in the past licenced for up to 220 persons till I assessed the means of escape- one stair of 1500mm but the other of only 900mm.
So I delved into all the guides and dd9999 but I cant stretch things beyond my recommended max of 150 persons- there is some capacity for queueing in the relative safety at the head of the narrow stair. Problem is with the approved guidance based on post war building studies that says 900mm=110 persons but 1050mm=220 persons. Cant find any empirical data to  justify going against this though. I can persuade the owner to go from existing M alarm to L1 but they are desperate to get back up to 200 and improvements to MOE not practicable. The L1 would be a huge advantage due to risk in the main stair from other occupiers (They are upgrading all doors to English  Heritage FD30 spec as well). But the bottom line remains that even with L1 for 200 persons in a traditional building using accepted capacity data the evacuation time is likely to be 4.5 minutes.

[wee brian]

The time when the narrow exits will be of most importance is when the fire is in the assembly hall. AFD will have no effect (for the reasons I set out above)

In theory you could try to reduce the fire risk (in terms of fire loading and ignition sources) but I doubt this is realistic in a multi purpose space.

Perhaps you could increase the size of the queing space by creating a foyer type space.