AFD for small kitchens

[Ken Taylor]

An estate of 'affordable' houses under construction with a few recently occupied as construction work is completed. The tiny kitchens are specified to have mains-powered heat detectors linked to ionisation type elsewhere. Use of toasters and opening of oven doors activate the detectors so the sound of sounders can regularly be heard from each of the occupied houses while annoyed residents frantically wave tea-towels, etc to silence the din as there are no silence buttons. Resiting within the kitchens would be pointless as they would still be within hot air reach of the cooking appliances. Detectors are not my expertise but I can see problems with both rate of rise and much fixed temperature detection here. Could someone recommend a suitable replacement detector before the rest of the estate joins the problem and owners start disconnecting the AFD?

[Graeme]

The joys of smoke alarms is you don't get much flexability. The heat with i.e Aico is a fixed temp at 54 degress i think.
The use of ionisation everywhere is not very clever and i always find outdated consultants specify them. Optical would be more suitable top reduce cooking alarms.

[Allen Higginson]

An estate of 'affordable' houses under construction with a few recently occupied as construction work is completed. The tiny kitchens are specified to have mains-powered heat detectors linked to ionisation type elsewhere. Use of toasters and opening of oven doors activate the detectors so the sound of sounders can regularly be heard from each of the occupied houses while annoyed residents frantically wave tea-towels, etc to silence the din as there are no silence buttons. Resiting within the kitchens would be pointless as they would still be within hot air reach of the cooking appliances. Detectors are not my expertise but I can see problems with both rate of rise and much fixed temperature detection here. Could someone recommend a suitable replacement detector before the rest of the estate joins the problem and owners start disconnecting the AFD?

Hi KEn - are they 100% sure that it's the heat detector activating and not smoke travelling out when they open the oven door or burn the toast.I have sheltered accomodation that has small kitchens opening onto the luving rooms and I get the complaint all the time that it's the detector in the kitchen going off for the reasons you give,due to the association of door opening or toast burning with the closest detetcor.

[kurnal]

What is the layout of the houses? Is the kichen an inner room off the lounge or dining area? Is it a room in itself with a doorway or is it just part of another room?
Does it open immediately onto the stairway?  How big is it?
Any ventilation in the kitchens? Any downstands to the ceiling if open plan?

Are we certain it is the heat detector in the kitchen ooperating- its more likely to be a ion detector  that could be some distance away ?
If we are certain its the heat detector operating then it is most surprising. If you really do need a detector in the kitchen due to the layout then and a rate of rise detector is giving problems then change it to a fixed temp type. But my money says that it is a nearby ion detector operating.

[Ken Taylor]

It's the heat detector Buzz and Kurnal. The kitchens are about 8m2 directly off the entrance halls and separated by a door. Ventilation by an openable casement window. There is no false ceiling. The heat detector sounder activates first and when the door is closed. The interlinked ionisation detectors are located in the hall and landing above. The heat detector is mounted in the centre of the ceiling and the position of cupboards and work surfaces around the room is such that hot air from the oven when opened must rise straight into it. I've come across this sort of problem before in larger commercial type cooking areas where moving the detector has solved the problem but it's not going to work in this case. Given that sudden temperature rise occurs and that 250 deg or so is possible from ovens, is there a heat detector that could be used here to do only the job for which they are intended or would another (non-ionisation) type be realistic?

[kurnal]

I suppose some simple calcs could be done to show the temperature at ceiling level when that convective plume from opening the oven rises to the ceiling entraining cool air as it goes and forming a layer across the ceiling. But that may be overkill- a slow response fixed temp heat detector  ( See the recent thread on heat /smoke detectors started by Davo) will surely be the answer here. It appears that many manufacturers will offer a choice of fast or slow response (EN54), and a choice of operating temperatures, but the techie guys will advise you best.

Looks like Ive lost my shirt again then.

[Allen Higginson]

I suppose some simple calcs could be done to show the temperature at ceiling level when that convective plume from opening the oven rises to the ceiling entraining cool air as it goes and forming a layer across the ceiling. But that may be overkill- a slow response fixed temp heat detector  ( See the recent thread on heat /smoke detectors started by Davo) will surely be the answer here. It appears that many manufacturers will offer a choice of fast or slow response (EN54), and a choice of operating temperatures, but the techie guys will advise you best.

Looks like Ive lost my shirt again then.

I'd lend you mine but.....anyway,a higher,slower responding fixed temperature or a delay would appear to be the answer if it was a fire alarm system as such.
In this case the best solution would be to (1) install a detector with a hush facility or (ii)  see if it can be removed due to it causing so many false alarms and possibly causing complacency.
Quite a good guide here from Aico in relation to mains detection and Part 6 - http://www.aico.co.uk/downloads/product_guide.pdf

[Ken Taylor]

I somehow doubt that the architect, developer and Building Control will agree to not having AFD in all the kitchens in this development but changing to detectors with silence buttons might be on. However, a recommendation from someone in 'the business' who has successfully used a type that overcomes the false alarm option would be most welcome. Just shows that simply saying 'put a heat detector in each kitchen' isn't always the right decision.

[kurnal]

Yes Buz, and aico have recently produced that multi sensor domestic alarm we discussed in a recent thread. I cant remember whether it operates on heat OR smoke independently or whether it needs both triggers to alarm. If the latter, and as it has an optical smoke sensor it could be what Ken needs

[Gel]

Domestic heat alarms are triggered at 57oC or 132F in old money.

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