location of detectors

[xan]

Could someone please explain the thinking behind why an L1 system may not have detectors in staircase lobbies,but L2 systems would (BS5839-1 para 8.2.)thanks in advance

[xan]

Have I asked such a stupid question that nobody can be bothered to reply?:-(

or to use a technical term found elseware on this forum,am I being a plank?

[Galeon]

No , we are all having our tea , and i am getting back to mine , watch this space no doubt once the boys have had their cheese and biscuits the replies will appear.

[xan]

ah, yes,I forgot I was out of office hours.

[Benzerari]

Could someone please explain the thinking behind why an L1 system may not have detectors in staircase lobbies,but L2 systems would (BS5839-1 para 8.2.)thanks in advance

Have I asked such a stupid question that nobody can be bothered to reply?:-(

or to use a technical term found elsewhere on this forum, am I being a plank?

Not at all, it's very good question, bear in mind, not all members knows the answer including myself, and who knows probably he needs a bit of time to answer correctly

[kurnal]

I dont know but offer the following possible explanations?

Explanation 1
An L1  system has detector coverage in all rooms and spaces. The staircase lobby will be sterile and contain no fire risk by definition. because all other spaces have detection a fire will be detected as soon as it occurs and the earliest warning will be given.

An L2 system does not necessarily have detection in all rooms and staircases, indeed it may not even have detectors in rooms leading off short corridors less than 4m in length- see paras 8.2 c,d and e. So it is less certain that a fire will be detected before smoke may enter escape routes - a detecto in the lobby may give enhanced protection to the stair for this reason.

Explanation 2-
It might be a cock up.

[Benzerari]

Also in practice there are still doggie things far away from the right interpretation and/or application of the theory:

I may add the following queries to the one initiated by Xan:

I used to see during servicing or commissioning, systems between L1 and L2 some times systems between L2 and L3, which didn't make sense to me. I have been told several times that, just mention it in the service/commissioning sheet and that's it.

         1.   Imagine an L2 system, having some rooms opens to the main corridors with detection and some others, open to the main corridor as well no having any detection? This didn't make sense to me...

         2.   Imagine an L2 system with electrical room of (2m*3m) surface open to the main corridor, considered as a simple small cupboard and not having any detection, and the worst thing is, it's a cleaner room at the same time with a sink…. and water installation above electrical distribution units some of them are HV...

         3.   Imagine in three months time any thing could happen, the building gets new alterations, cut of fire cabling… and so on, all of that without prior consultation of the main alarm service company, where normally an up to date fire risk assessment has to take place, but no one bother about, only when a fault comes up on the fire alarm system, they call the alarm service company to sort it out as a separately issue…

Imagine and imagine and imagine…

[CivvyFSO]

I can think of an example that would explain:

Imagine a simple 5 storey building with lobbies. You sit on the top floor working away, or trying to help people on firenet. A fire occurs on the storage area on the ground floor that is not part of the escape route for anyone. This storage area is adjacent to the lobbies. (You could argue about a storage area actually being an escape route for someone, but that is not the point I am trying to make)

Now, install an L2 system. You need detection in the lobbies to warn you of this fire as there is no requirement to detect the 'non-escape route' part, and it is removed from your escape route by 1 room (The lobby) Without detection in the lobby the first thing you will know is when smoke has entered the stair.

Now install an L1. You don't need detection in the lobby as this fire is already picked up in it's infancy. (There should be no risk in the lobby at all, as Kurnal pointed out.)

I am sure that the same reasoning could be used to warrant the detectors being omitted from the lobbies in an L2 system providing that the room/corridor that opens onto the lobby has detection in it.

[xan]

Ok,thanks for your replies,(some of them echoed my own thoughts and reasoning,but I wasn't convinced)so:
if you had an L2 system it is possible to have a room opening onto a corridoor less than 4m in length,not having a detector,therefore a requirement for detection in a lobby (as explained earlier),but,if you have an L1 system,as that same room would now require a detector(with the exceptions as quoted in para 8(2)(f)-toilets etc) there is no need for a detector in the lobby,as any fire would be detected much earlier.Does that sound reasonable?

[CivvyFSO]

I think so. Although you may get another answer from some of the alarm gurus on here.

[Benzerari]

Also 'L1' usually is 'L2' + (...... other rooms... etc), Just like 'L2' is 'L3' + (.... other rooms... etc)

In fact now:


                                  'L1' = 'L2' + (... other rooms... etc) - (Stair's landings)


Heard it for the first time, every day is a school day

[Davo]

Always assuming of course that some plank doesn't put vending machines and the like in the corridors/lobbies
Always assuming you don't get a batch of aging light fittings.......

davo

so speaketh the voice of (limited) experience

[colin todd]

If low risk areas and lobbies can be omitted in an L1 system, it is ok to omit them from protection in L2 and L3. It does not explicitly say that in BS 5839-1, because it was thought to be intuitive.

[PhilB]

Colllin Toddy!!!! I remember him! Where have you been old boy?

[colin todd]

Keeping busy, Phillip, trying to keep on the straight and narrow all the people your erstwhile employer never trained right in the first place. As you can imagine, thats a very full time job.