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Posted By Oompaloompa
Hi everybody,
First time poster......
Just occured to me whilst arranging our annual 3 hour emergency lighting tests - Why 3 hours?
If you work on the premise that emergency escape lighting is provided to allow occupants to exit the building in the event opf a power failure - Surely we would not expect said occupants to still be in the building after 3 hours?
Just a thought.......
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Posted By PMW
As an aid for emergency services?
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Posted By Stuff4blokes
Hi Oom. This was a discussion point on the course I was recently on. Nobody came up with any real credible answer other then "it says so in the British Standard"
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Posted By DaGuru
you should consider the emergency services personnel that will be entering the building after the alarm is raised.
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Posted By DaGuru
what PMW said.....echo in here!
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Posted By D H
To assist the Emergency services? That is assuming that in a major fire the emergency lighting will still be intact!
Good question!! Does anyone know the real reason? I certainly do not.
Dave
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Posted By PMW
Thats assuming that the emergency services are attending because of a fire. Consider a gas leak, an accident which resulted in loss of power and paramedics need access to assist injured, Malicious damage - therefore police would attend, could be lots of possibilities.
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Posted By Oompaloompa
Thanks for all your responses.
Like some people, I assumed that the extended period was to provide a level of illumination for protracted evacuations and the emergency services etc.
However, I am still curious about how a period of 3 hours was established, as opposed to, say,1, 2 or 4 hours?
Was 3 hours the maximum period that could be reasonably achieved at the time? If so, has the technology moved on since then?
Or was 3 hours considered a reasonable period to resolve a "typical" emergency?
Or was the figure arrived at in a more random fashion?
Anyone still around who was involved in the process and can shed more light on the matter (Sorry, couldn't resist!)?
Thanks
O
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Posted By martinw
Found this - hope it helps
The duration of the battery system is decided by:
Three hour duration is required in places of entertainment and for buildings where people may be sleeping.
Three hour duration is required if evacuation is not immediate, or early re-occupation is likely to occur.
One hour duration may be acceptable, in some premises, if evacuation is immediate and re-occupation is delayed until a full recharge of the system has occurred. In practice it is normally preferable to choose a three hour system.
Info comes indirectly from EN 50172: 2004, highly paraphrased to avoid copyright issues!
Martin
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Posted By Jim Tassell (2)
I have always been taught that three hour discharge has little to do with fire safety directly; it's simply to make sure the batteries are totally discharged occasionally. "Memory effect" and suchlike can render continuously trickle-charged cells prone to unpredictable early failure (which we don't want!)
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