Re: Domestic detectors- heat or smoke

[david911cockburn@btintern]

Hi All,
Sorry to butt in on your thread, but the use of 'smoke' detectors in flats seems strange to me.
As far as I was aware the Law can't and therefore doesn't usually attempt to "protect people from their own stupidity". Therefore within a block of flats I would of assumed that the first people to consider would be the neighbours, therefore with the benefit of hindsight would it not make more sense to use 'heat' detectors?
It would appear that in the real world people don't like smoke detectors (they are a pain), they wouldn't even notice that they had a heat detector until the twerp downstairs tried to burn them alive.
Just a thought.

[David Rooney]

As far as I was aware the Law can't and therefore doesn't usually attempt to "protect people from their own stupidity".

I think the health and safety at work act 1974 and just about every dictate from the HSE are aimed at protecting people from their own stupidity in one way shape or form......

Smoke detectors can be a pain but I'd rather be woken by smoke creeping up the stairs than flames licking at my bedroom door.

[kurnal]

What happens in peoples private dwellings is their own private concern and the health and safety at work act does not apply. However the benefits of smoke detectors can clearly be seen from the fire death statistics. Back in the 1970s around about 750 people a year used to die in fires their own homes. Nowadays fire deaths are around half that number for three main  reasons.
1 The building regulations have required all new homes to be fitted with mains powered smoke alarms since 1991
2 The fire brigades have done a sterling job in raising public fire safety awareness and encouraging the installation of smoke alarms
3 upholstered furniture is less hazardous than it used to be.


The essence of safe design in flats is based on the concept of fire compartmentation-ensuring that any fire can be contained within the flat of origin without a risk of spreading to neighbouring flats.

[AnthonyB]

If you were talking about a communal system for a whole block then you might (only might) be right. But in this case it was a single station smoke alarm provided solely for the life safety of the occupants of that particular flat - a heat detector would be no use as occupants could be trapped or incapacitated before it triggered.

Please don't let this turn into a mega-thread about the different types, extent & categories of fire alarm systems in dwellings, flats, HMO's etc - i could do without a headache!

[kurnal]

Drug legislation?
Alcohol age limits?
The Building Regulations?
Speed restrictors on motorcycles?
Seat belt legislation?

To name a few.

It would be pointless putting common areas fire alarm systems in blocks of flats designed for a stay put policy. Designers and electricians often insist on putting them in buildings where they are unnecessary or undesirable and I often recommend that they should be removed.
Please stop installing them unless the fire strategy for the building really relies on them. In flats there is little point. Unless you also put sounders in flats people cant hear the alarm. If they do hear the alarm they most likely dont need to evacuate anyway unless its their flat thats on fire, most dont bother to evacuate or respond to the alarm except to vandalise the panel to shut it up.
We must instead make sure that the compartmentation is installed and is maintained to a good standard capable of containing the fire to the flat of origin for long enough for the fire to consume all the fuel therin.

[kurnal]

I disagree David. The purpose of the fire alarm system is to warn occupants of the building for as long as is necessary in accordance with the fire evacuation strategy of the building. In some buildings with staged fire alarm systems enhanced protection is necessary for this reason.

But the fire alarm can fall off the wall as soon as everybody is outside. It certainly does not need to continue sounding as the building collapses.
Grumpy? No. but we dont need to reinvent the wheel. The fire strategy for flats has evolved since the last war in the  light of experience, purpose built flats without fire alarms in the common areas remain perfectly safe so long as people maintain and manage them correctly. And if they dont a fire alarm system does not make things significantly better.

I suggest you have a read of BS CP3 Chapter 4 part 1- any version from 1947-1971 and BS5588 part 1 if you are interested in reading  more on the background to the fire strategy for flats. All available online through your public library.

[Midland Retty]

Hi David

Ordinarily blocks of flats aren't fitted with automatic fire detection.

That said new apartments should have stand alone mains powered smoke detectors provided (Building reg stipulation).

If for argument sake a communal fire alarm system is required throughout a block of flats you will normally have smoke detectors protecting the communal areas, interlinked heat detection within each individual flat complete with a stand alone smoke detector. The stand alone smoke detector doesn't need to be wired to the panel, instead the heat detector will eventually alert the building that a genuine fire is in progress.

So the stand alone smoke detector is purely to warn the person in the flat of a fire, the heat detector warns everyone else in the block of a fire and this configuration prevents unwanted fire signals / false alarms.

[kurnal]

This is standard practice in those buildings where a "stay Put" policy is inappropriate, for example if the building does not have the necessary compartmentation or ventilation to the exit routes etc. Also in sheltered housing schemes.

[Midland Retty]

I'm not sure that it would have any benefit David. You could still get false alarm problems with that configuration.

[kurnal]

Thanks Kurnal,
As for evacuation (you miserable old scrote) if your system is still on the wall when the Fire Service arrives, it can provide them with some very useful information especially about the location of the fire; and theoretically the sounder system can do the something similar.
Admittedly minimum requirements have to be available, especially when cost is a factor.

The location of the fire will probably be self evident in those circumstances as they drive up the road

The fire alarm may give some indication of where the fire started if it survives the fire, if it is an addressable system and the memory has sufficient capacity but there are many other indications that would be relied on in the event of a fire investigation.
I think perhaps you worry too much!

Yes it is standard practice to have a staged response to a fire, it is standard practice in many buildings, gives the management time to investigate the cause of the alarm before tipping people out and with sensitive detection can enable fires to b discovered and dealt with in their incipient stages before they become a bigger hazard. Its a good way of striking a balance between sensitive detection and disruption. Another place it is universally applied is in shopping centres.

[Midland Retty]

Hi Midland fire,
It would only be 'fine tuning' what you already said, a time delayed smoke detector would detect smoke from a room behind a closed door, whereas a heat detector would wait for the fire to enter the room/hallway it was located in.
Theoretically you could gain quite a few minutes.

You could still get false alarm issues with that configuration, and of course if you did have an interlinked (albeit delayed) smoke detector then why would you need the heat detector too?

Also worth bearing in mind that the level of fire separation / compartmentation in a building also governs what type of system you would require.

[Midland Retty]

Hi David

My intepretation of what your saying is this:

In a flat you would install a smoke detector linked to the buildings fire alarm panel. After a set time delay the smoke detector will trigger the panel to go into full alarm which activates the communal fire alarm sounders.

To me this serves no purpose whatsoever because it duplicates the role of the heat detector (ie to warn all occupants of a fire in one the flats) and most importantly you could get false alarm issues.

A stand alone smoke detector on the other hand is designed to protect the occupant of the flat only and if activated would only sound locally within the flat.

If someone chooses to cover their own smoke detector then they are only putting themselves at risk.

If they covered the heat detector they could be putting other people at risk.

Remember that detection isn't there for the protection of the person in the flat of fire origin, it is there to protect the means of escape and give warning to other people.

The other problem with a time delay on the smoke detection is this. How would you stop it from activating after the time delay? Would someone need to go down to the fire panel and cancel it? If so would the resident know how to reset the system?

[Midland Retty]

You are over complicating the matter

If you are going to have an interlinked smoke detector then you dont need the interlinked heat detector simple as that, and in which case a delayed activation function should not be entertained for a "sleeping risk" scenario anyway. So either interlinked smoke or interlinked heat, but not both.

If you choose an interlinked smoke you risk getting false alarms, if for example you have an apartment or bedsit with cooking facilities.

That is why interlinked heat detectors are utlisied with stand alone smoke detection for localised protection.

The standalone smoke detector will hopefully rouse the family in your scenario if a fire were to occur, just as an interlinked one would.

Your argument that smoke detectors react quicker than heat detection is quite true - but either have one or the other linked to the communal fire alarm, don't have both. There is no point.

[kurnal]

David I think you are creating complicated solutions to problems that do not exist or do exist but without causing signifcant hazards. The medication you prescribe creates worse symptoms than the ailment.

For this reason I am out.

[David Rooney]

Hi Kurnal/All,
I'm rather glad that I carried on worrying. I've been doing some reading but I didn't have to go to the Library, its' quite literally been right under my nose all day.

I am referring to BS 5839-1:2002, Section 2, Figure 1a) - Radial sounder CIRCUITS (notice this is plural).
Our author has used 'ambiguity' in order to relieve himself of the burden of responsibility.
Radial sounder circuits (plural) should refer to two or more radial circuits, which are circuits supplied by a 'radial feeder' to a central 'junction box' with any number of 'stub end feeders' (or spurs) from the junction box each supplying one socket outlet/light fitting/bell.
But in this case 'Radial sounder circuits' (plural) refers to two different circuits, one spur final circuit and one final circuit (or one zone), supplied in a manner that can be described as radial.

This drawing is not labelled as being a 'radial system', but we actually are using 'radial system' components (sounders).
In effect the author has not accepted the legal responsibility for the use of radial system sounders!

What exactly are you arguing ...... the definition of a radial circuit, is that it?

Everyone in the fire detection industry understands a radial circuit generally speaking to be a single cable wired from point to point. It has a beginning and an end and has no spurs coming off of it. Although even if it did this only presents problems from a fault monitoring point of view - pretty much as diagram 1a to which you refer indicates.

These circuits will carry Extra Low Voltage at  24 volts dc (give or take) supplied by a safety isolating transformer within the CIE meeting EN54-4.

Are you trying to say that our ELV "radial circuits" are electrically dangerous ?