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westminster
06-07-2010, 14:10 PM
Tenants have complained that the mains-wired optical smoke alarm keeps going off when they cook. (It's the second lot of tenants to complain, so I know I need to do something about it. All the smoke alarms in the house are wired together, and all go off if one gets set off, so the noise is a real nuisance).

Anyway, my first thought was just to replace it with a heat alarm instead, (easily done as the base unit wired to the ceiling is the same whichever type of detector you have, and the latter clips on to the base) but then I wondered if that's the right solution. Perhaps heat alarms need to be closer to the potential fire risk than smoke alarms?

The room is an open plan sitting room/kitchen, about 20ft x 15ft. The existing alarm is about 6 ft away from the hob/oven. Perhaps the problem is it's too close?

So, should I:

1) Replace smoke alarm with heat alarm
2) Keep smoke alarm but move it further from hob/oven
3) Replace smoke alarm with heat alarm and move position (closer to hob?)

2) and 3) involve the additional expense of an electrician and patching up the ceiling, so hope the answer is 1).

Darren Baird
06-07-2010, 14:23 PM
I'm afraid it would be option 2 for me. Heat detectors generally do not operate until the flames are about 2/3rds the height of the room, you need much earlier warning than that for the home and they won't detect smoke only heat by which time it may well be too late for the occupants. They are normally located in kitchens and boiler rooms etc

Try moving the detector as 6m does seem a bit close. Or change the current smoke for a heat and provide a new smoke detector further away from the cooking source in the room? You could also find out what type of smoke detector it i.e. optical or ionisation. See info below for you.

The Optical Smoke Alarm


This type of smoke alarm uses light technology to detect smoke. Inside of these alarms, there is a small light emitting diode or LED. This little light shines a thin beam of infrared light to a sensor. If any small particles of smoke interrupt this infrared light the voltage read by the sensor will drop and the alarm will sound. This type of smoke alarm is best where the threat of smoldering, thicker smoke is present.


The Ionisation Smoke Alarm


This type of smoke alarm employees a completely different technology to detect smoke particles in the air. This type of smoke detector has about one milligram of radioactive metal in it, that has been scientifically proven safe for humans. The sensor part of the smoke alarm is called an ionisation chamber. Inside of this chamber there are a small amount of electrodes with a current running through them.


If a small particle of smoke enters the chamber it ionises the radioactive element in the alarm and the current flowing between the electrodes is interrupted. This causes the alarm to sound. This type of detector is good at detecting smoke when the fire is more flaming than smoke producing because it can detect such small particles.


Which Is Better?


Ionisation smoke detectors can detect smoke quicker than optical smoke alarms due to the difference in technology. However, the ion type of smoke detectors are extremely sensitive and can cause more false alarms than there optical counterparts.


Many manufacturers are starting to discontinue product of ion smoke detectors because of advances in optical smoke detection technology. Those that continue to produce both ion and optical smoke alarms usually house them in the same outer casing.


The only real way to determine which type of detector you are buying is to read the packaging that comes with your smoke detector. Ion detectors are more sensitive and expensive, while optical smoke detectors are cheaper but less sensitive.


In order to get the best of both worlds you should employ both types of detector in your home.

westminster
06-07-2010, 16:16 PM
Thanks for your reply.


I'm afraid it would be option 2 for me. Heat detectors generally do not operate until the flames are about 2/3rds the height of the room, you need much earlier warning than that for the home and they won't detect smoke only heat by which time it may well be too late for the occupants. They are normally located in kitchens and boiler rooms etc
Yes, that's what I understood to be the case, so why would a heat alarm not be appropriate for this kitchen?


Try moving the detector as 6m does seem a bit close. Or change the current smoke for a heat and provide a new smoke detector further away from the cooking source in the room? You could also find out what type of smoke detector it i.e. optical or ionisation.
It's an optical smoke detector. I have an identical one in my kitchen, only 3 ft away from the hob/oven, and have never had a false alarm, so don't understand why the one in the rental property, which is twice as far away, is being triggered. The only difference is that I have a ceramic hob whereas the rental property has a gas hob. Could this be the reason?

In addition, all the smoke alarms' positions were approved by the building control officer, as they were installed in 2007 as part of major works. The stairs to upstairs are also open plan and on the first landing there's another smoke detector - would this be close enough to be a 'back up' to a heat alarm (given that smoke rises and would have a clear passage to this mezzanine smoke alarm)?

It may or may not be relevant to know that the official primary fire exit is actually upstairs, not downstairs where the open plan kitchen is (hence I was allowed by building control to make the kitchen open plan).