fire alarms and heat detectors

[Fred]

Hello,

I am a bit puzzled about heat detectors [that should be interlinked with smoke detectors]. I understand that a smoke detector in a kitchen could have false alarms and that this is why a heat detector is used but I read a manufacturer's site that claimed building regs. say a heat detector should be used in the lounge ("principle residential room"). Is this true? Why should a heat detector be needed here if you have a smoke detector?

If these alarm when the temperature reaches 56C, how useful are they? I am guessing a fire goes from room temperature to very, very hot very quickly. Is a warning at 56C likely to be useful or by then won't it be too late? Is the idea that it may be too late to save the kitchen/lounge but it will wake you and get you our of bed before the fire spreads?

Would you bother putting heat detectors in the garage and loft?

TIA

[ARWadsworth]

It would normally be a smoke alarm not a heat detector in the lounge. Smoke detectors need to be in the circulation spaces of a house (hallway and landing)

Ideal for a kitchen fire.

I would not bother with one in the loft, but I would put a heat detector in the garage.

I see your email address is not valid. Mine is, so if you email me via hotmail or some other temporary address I will send you the BS5839-6-2004 "Fire detection and fire alarm systems for buildings" pdf if you fancy a read. The offer applies to anyone not just the OP.

Cheers

[Spamlet]

Good grief its £196!

But here is another pdf about it, and you can google for lots more:

[Fred]

I think some may not be as sophisticated as alarming based on the rate of increase of temperature. Kidde told me there models alarm at 56C, implying the rate at which it gets to 56 degrees doesn't make any difference on their models.

So does it need to be as close to the hob as possible then? I'm thinking by the time it gets 56C at the other side of the kitchen it might be too late?

The pdf I read was here:

5, question 12 (continued) talks about fitting heat alarm with a smoke detector in the lounge. I can't understand why (except to generate more sales!)

I wondered whether to have a heat alarm in the loft since nothing else is suitable. Hopefully the upstairs light radial will never get hot enough to start a fire! Other than that there is only the tv amplifier up there but the problem with loft wiring is it is out of sight, out of mind. OTOH by the time the loft gets to 56C I imagine everything that can catch fire is already alight? BTW it is an unconverted loft, used only for storage, so plenty of flammable cardboard boxes.

[Fred]

Thanks that is very kind. I will be in touch.

[Fred]

I thought this was a very good point worth emphasizing. I hadn't appreciated that the smoke might "float" along the ceiling and up the stairs before triggering the alarm in the same room as the fire. Does all smoke rise? Is there none heavier than air that crawls along the floor?

[Peter Parry]

Same goes for fixed trigger point alarms. By the time the ceiling in the living room is at 58C your chances of survival if you are in bed are very poor.

Correct, the role of the alarms differs. "Products of combustion" (ionisation and optical) alarms are designed to detect a fire before it becomes established. They should detect smoldering material for example. Fixed temperature alarms detect established flames. In a kitchen you need to identify where a fire is most likely to start - usually the hob, sometimes the oven, and put the alarm on the ceiling fairly close to those areas so any hot gasses from the fire go over it. At least a foot out from the wall and above the risk area is where you want them to be.

Neither do I. There is a huge problem with BS5839 however. While it merrily sprinkles alarms throughout a house it ignores the effects of nuisance alarms ( a nuisance alarm isn't a false alarm but an insignificant one. A piece of toast overcooking for example).

The more sensors you have the more prone to nuisance alarms the system as a whole becomes and the more likely it is that people will disable them. Too many sensors can be more harmful than too few.

The chances of a fire starting in a loft are very small. It probably won't hurt to put one there but it isn't going to make the house safer.

[Peter Parry]

Smoke doesn't but the invisible gasses produced in combustion do. In almost all house fires the ceiling alarm above the stair well triggers first as the stream of combustion gasses rises and spreads.

Once you have one alarm in the downstairs hall (near the living room not the kitchen) and one on the upstairs landing ceiling you have got about 95% effectiveness. A temperature alarm in the kitchen above the cooking area would be the next priority. Personally I'd stop there. If you have any very heavy sleepers, people who use sleeping pills or who use sound muffling ear inserts to sleep then consider putting a linked alarm in their room. It isn't to detect fire - just to make more noise where it is needed when another alarm goes off.

Don't forget that all these alarms are useless unless you also know what you are going to do when they go off at 03:00. You have a minute or so to get out so this is not a good time to start thinking about your escape plan. In particular make sure all exit doors have locks that can be opened from the inside without needing keys. If they can't and you won't replace them (fires kill far more than burglars) then make sure a key is permanently wired to the handle so it can't be dropped.

If you have double glazing in bedroom windows get a few automatic nail punches such as

clip them near the windows. Pressing one onto a double glazed pane near a corner will break it, throwing chairs and bedroom furniture at it won't..

Having got your plan make sure everyone knows what it is :-).

[ARWadsworth]

Well it obviously is not £196 from some places;-)

[Fred]

Sorry for the late reply. Thanks for all the informative replies.

The heat alarm in the kitchen is a metre or so away from the hob, so when the kitchen gets redecorated, I will try and move it across.

I know what you mean. I had some optical alarms that would go off at 3 in the morning. Never found out why. I blamed insects. Can spiders get in or is the sensor too small? Perhaps we have a very dusty house! In the end I replaced them with ionization ones.

I don't know whether I'll put one in the loft or not. OTOH you don't go up there much so you wouldn't see or smell any warning signs but I do wonder if by the time a heat alarm had been activated whether the loft would have burnt down.

Thanks again.

[Dave]

When I had the part time job as school site supervisor, I came to unlock and take the alarm off once, and there was an alarm activation sheet next to the door. They had to call out the alarm Co, who found that alarm had been triggered by a spider that had got inside the infra red heat sensor. When you think about it, the spider would have changed the heat reflection as it crawled over it, or the window the sensor looked out of it.

Dave