VAS or Sounders

[David Rooney]

School premises is having a small detached block being built - 2 classrooms.

Consultant has asked for the existing PA/VAS to be extended to the area with two speakers - apparently off the same PA circuit.

My initial thought is that this doesn't comply with pt 8 due to "interleving" if the sounder zones etc.

Then I thought if we were installing fire alarm sounders we would only require one circuit in this new block to comply with pt 1 ?

Am I right or have I missed something !!

Can we use a single PA circuit and say it complies

[Galeon]

Dave ,
Was rooting about and found this post , better late than never , no you need a minimum of 2 speakers off the voice system , ie a & b circuit to comply , as you well know we have never interleaved alarm circuits in the fire game  for very obvious reasons . So you are right on with the one alarm circuit , as a short circuit shall not impair the operation of the other circuit , which I take it you already have.
I have had many rows with consultants over the years in relation to alarm circuits , on the fire alarm , they do eventually come round.

[Wiz]

Galeon,
Interleaving of fire alarm circuits has been a popular method of arranging fire alarm warning device circuits for many years (often because of misinterpretation of the concept described in an earlier BS recommendation) so I can't quite understand why you said 'we have never done this in the fire alarm game'. It has been done for years and it is still often specified by system designers.
Current BS does not say that interleaving is not recommended but it only indicates that it is not a necessity for most systems.
However, there is also actually a recommendation to 'interleave' in current BS for large compartments or those capable of accommodating more than 500 members of the public.

[Allen Higginson]

I was a bit confused there - by "interleaving" do you mean alternating bell circuits throughout?If this is the case then we done it for years so that you had a bell circuit ringing if one went down until it was deemed unnecessary in 2002:part 1 (unless as in the situation Wiz raised).

[Wiz]

Buzzard, yes, 'interleaving' is the 'technical'(!) term for what you describe. However, I'll think you will find that there was not a change in recommendations at 2002 'deeming interleaving unnecessary'. I don't think it ever was  necessary. I believe we all just misunderstood the 2 sounder circuit concept as it was described in previous BS versions and assumed interleaving was the best interpretation. Colin Todd's book (about BS5839 part 1 2002) gives a very interesting explanation of how the two (or more) sounder circuit concept is best met, and why. I won't try to explain it here because I often get accused by some on this forum of being too long-winded and too technical. therefore anyone wanting my summary of C.T.'s explanation can PM me for a copy.

[Galeon]

Wiz ,
Some people will now be totally perplexed , with these posts , as a point of clarity do we all agree on the last post you made that Toddy's version is what we should be aiming to achieve. I assumed in my original post that even going back over the years the way we (as a company) did the sounder configuration was correct.

[kurnal]

I have seen it commonly stated that the requirement in BS5839 for two sounder circuits can be met by placing a single sounder on its own circuit adjacent to the panel, the remainder in the building being all on the same circuit. Is this correct and in the spirit of the BS?

I see it tieing into emergency procedures and management. In the event of a failure of one circuit, will the remaining alarms be heard and acted upon by the building management?

Will the management appreciate the implications that many persons in the building may not have been able to hear an alarm?

If the panel is is a staffed area then this one sounder could be an acceptable approach- but what if it isnt?  

We know that generally people are slow to respond to the sound of a fire alarm- what would be the outcome if the alarm was only just audible or patchy?

Its a good job the alarm circuits are fault monitored and resilient!

I for one would be very interested in hearing your explanation Dr Wiz. Pretty please.

[Wiz]

Wiz ,
Some people will now be totally perplexed , with these posts , as a point of clarity do we all agree on the last post you made that Toddy's version is what we should be aiming to achieve. I assumed in my original post that even going back over the years the way we (as a company) did the sounder configuration was correct.

Galeon, of course I agree that we need to do as the BS recommends. I have no reason to believe that you (as a company) don't design and install sounder configurations that meet the recommendations. I was just pointing out that I thought your comment that 'we have never interleaved alarm circuits in the fire game' was inaccurate, partly because the current BS includes actual recommendations for doing so in certain situations, and partly because BS makes no recommendation stating that it musn't be done in general applications

[Wiz]

I have seen it commonly stated that the requirement in BS5839 for two sounder circuits can be met by placing a single sounder on its own circuit adjacent to the panel, the remainder in the building being all on the same circuit. Is this correct and in the spirit of the BS?

Yes, it is my understanding that this is correct and actually totally in the spirit of what BS is trying to achieve.

I for one would be very interested in hearing your explanation Dr Wiz. Pretty please.

Oh Prof., what are you doing? You know you don't need to say 'pretty please'. Now you're making it sound as if you can only get information from me if you beg. You of all people should know that is not the case. I only wanted to make sure that only those really interested in what C.T. has to say in his book have to put up with my long-winded summary.

[Allen Higginson]

I suppose there is now an assumption that the fire alarm systems installed today are either addressable or two-wire conventional,both of which doing away with seperate sounder circuits out in the field (thus saving wiring costs).This then means that won't only be depending on the sounder installed at the panel should failure occur out in the field (in say a short ) as (a) the isolators will only lose (if installed between zones) the sounders in the effected area or (b) in the case of the two wire system sounders will ring in the other zones.In the case of systems with isolators at each device you have in fact a theoritical situation of "virtual" multiple sounder circuits throughout the loop as either side of the isolator is still fed.
Furthermore,it is acceptable to have a loop powered sounder as the first device on the loop,protected by isolators isolators which,in effect,gives you a minimum of two sounder circuits

[Wiz]

I have received a number of requests to post my summary no matter how long-winded it is. So here we go - don't blame me if you get bored half-way through!

Summary by WIZ of the explanation in ‘A guide to the BS Code 5839-1;2002’ * regarding the recommendations in respect of installing two monitored fire alarm sounder circuits in fire alarm systems

The recommendation for two monitored sounder circuits first appeared in the 1980 version of the British Standard.

It soon became common within the fire alarm industry to interpret this recommendation so that both circuits were installed in all (or virtually all) areas of a building. The concept of this interpretation was that if one fire alarm sounder circuit ‘failed’ for any reason then sounders connected to the other circuit would still continue to operate and that by having an ‘even spread’ of sounders, a fire alarm warning signal would still probably be heard throughout the building.

The guide states that the BS recommendation was widely misunderstood and it was never intended to provide this level of integrity. It further suggests that installing two circuits throughout the building may, in fact, be less satisfactory in respect of the primary reason for the  two circuit recommendation (explained below)

The guide suggests that the primary concern of failure of the fire alarm warning signal (for any reason) is that persons who had already evacuated a building upon hearing the fire alarm warning signal, might automatically assume, upon cessation of the fire alarm warning signal due to a fault, that the danger is over and that the fire alarm system has been reset and that it is safe to re-enter the building.

The guide suggests that it is felt that a fault on a fire alarm signal warning circuit is unlikely before or during the early stages of a fire but that a serious fire is more likely to cause the failure of a sounder circuit some time after the building has been evacuated.

The guide suggests that people are likely to re-enter a previously evacuated building through an entrance that is close to where the fire alarm control panel is located. Therefore if a fire alarm warning sounder is specifically located in the vicinity of the fire alarm system control panel and is connected to one of the monitored sounder circuits and that this circuit is not extended into other parts of the building then this sounder is likely to continue operating throughout the fire and so people will not re-enter the building whilst danger is still present.

BS 5839 part 1 contains a drawing (Figure 1a) of the recommended layout of radial sounder circuits and this clearly shows the above interpretation of the recommendation with Sounder Circuit One connected to a single sounder ‘normally located in the vicinity of the control panel’ and Sounder Circuit two connected to a number of ‘sounders serving the remainder of the building’.

The concept of the recommendation is extended to loop-powered sounders on addressable systems by recommending that one of the loop sounders is located close to the control panel and protected on each side of the loop by a short-circuit isolator.

End

* Fire Detection And Alarm Systems. A guide to the BS code BS5839- 1: 2002 By Colin Todd.   ISBN 0 86213 129 4

[Galeon]

Wiz
Tip top me old son .