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FIRE SERVICE AND GENERAL FIRE SAFETY TOPICS => Fire Safety => Topic started by: Guest on August 26, 2004, 01:24:34 PM

Title: BS5839
Post by: Guest on August 26, 2004, 01:24:34 PM

BS5839: Pt6: 1995 Fire Detection and Fire Alarm Systems for Buildings


Why do smoke alarms which derive their power from the mains lighting unswitched circuit have a battery back when new homes with a dedicated unswitched circuit don't?

Thanks

Mark

Im sorry that I have posted this on two forums but I am unsure as to which thread would be more relevant.

Title: BS5839
Post by: wee brian on August 27, 2004, 07:35:30 AM

Because the lighting circuit is presumed to be more likely to fail than an independant one.

Title: BS5839
Post by: JamesG on August 27, 2004, 08:01:33 AM

A point worth noting (possibly?).  The standard you have quoted has been superceded by a later issue (2002, i think).  Haven't read it in the last few months, so can't tell you if it has changed regarding your question..

James

Title: BS5839
Post by: Guest on August 28, 2004, 12:53:52 AM

Yje 1005 version is still the current one. The new Part 6 will not be published until mext month. It will advocate mains with a standby supply for all new dwellings.

Title: BS5839
Post by: JamesG on August 31, 2004, 08:57:07 AM

Sorry, I was being a bit dense and not reading the posting properly. I was thinking of BS 5839 part 1.

Title: BS5839
Post by: Guest on September 01, 2004, 03:38:13 PM

Hi

Wee Brian, why would a lighting circuit fail more often than a normal ring main..... and so that BATT back up is required?

Does the alarm still have to sound and send a signal to an interconnected alarm?

Iv'e heard it has something to do that if a fire were to occur the wiring would be one of the first things to disintegrate......so whats the point of batt back up to send a signal to another alarm.....when its probably melted away??? Is this just BS confusion or marketing confusion.... is there a clause stipulated for domestic properties?

Thanks

Title: BS5839
Post by: wee brian on September 01, 2004, 10:05:50 PM

I chose my words carefully - "it is pressumed" - so I don't necesarily understand it myself.

In practice most housebuilders use battery backup alarms powered by the lighting circuit. It worlk out easier and cheaper than providing a seperate circuit.

Title: BS5839
Post by: colin todd on September 04, 2004, 03:13:17 PM

Brian, What do you not understand? Please bullet point the points, so that a simple explanation can be given to you. It is important that you do understand if ADB is to make any sense.

Title: BS5839
Post by: wee brian on September 06, 2004, 05:02:25 PM

Colin

Why did we ask for battery back up for alarms powered by the lgihting circuit and note for alarms with their own supply.

I appreciate that there is a concern that the lighting circuit may be less reliable in an emergency but I am not sure exactly why.

Is that a clear enough question?

Title: BS5839
Post by: Guest on September 06, 2004, 07:43:50 PM

In  a fire situation the lighting circuit is nearly always the first to trip off,,,,,,highest point.moisture from condensation of pyrolysis products andheat etc Ring mains offer greater protction to the wiring due to low level.Ive been to loads where only the lighting circuit has gone out...Also it was told to me that a person would probably notice a lighting circuit out before a ring main and could therefore get the circuit back on.I dealt with a fatal a few years ago and contacted a national SD maker who told me the battery should last for,2hours at full decibel output,after mains failure...didnt help my guy though,,vodka makes you deaf .

Title: BS5839
Post by: Guest on September 07, 2004, 07:54:18 PM

Hi

Thanks for that Potter, Colin has also replied on Comm forum [and myself] if you would like to view thread.

Many thanks for your reply