Alarm Type Selection

Smoking Ban in Public Places
Please note that smoke alarms are not designed to react to normal levels of smoke
emitted from cigarettes etc.
However, that should not deter you from fitting them where smokers are present, as there
is a greatly increased risk of fires starting in such locations eg cigarette dropped down furniture. 

There are 2 types of smoke alarm sensor as detailed below.

For best overall protection Kidde recommends a minimum of 1 of each type of alarm.
See guidance below.

Ionisation Alarms (also known as ION):

Ionisation sensing alarms may detect invisible fire particles (associated with fast flaming fires)
sooner than photoelectric alarms.

React to small particles that are often invisible to the human eye e.g. polyurethane foam, as
used in older furniture.
More prone to nuisance alarm from steam/invisible cooking particles that may be generated if
located too close to kitchens for example.

Available in mains, mains with battery or battery configurations.
The ion chamber consists of several plates with a voltage across them, along with a radioactive source of ionising radiation.

See illustration.

This results in a free electron (with a negative charge) and an atom missing one electron (with a positive charge).
The negative electron is attracted to the plate with the positive voltage, and the positive atom is
attracted to the plate with the negative voltage (opposites attract).

The alarm's electronics sense the small amounts of electrical current that these electrons and ions
moving towards the plates represent.
When smoke enters the ionisation chamber it disrupts the current.

The smoke particles attach to the ions and neutralize them & alarm senses the drop in current
between the plates and sounds the alarm.
These alarms contain a tiny amount of radioactive material, but well within accepted safe levels. 

Optical Alarms (Photo Electric):

Best suited to slow smouldering fires as illustrated. eg. PVC cabling/foam filled furniture/bedding material/electrical appliances.

Photoelectric(Optical) sensing alarms may detect visible fire particles
(associated with slow smouldering fires) sooner than ionisation alarms.

Increasingly popular because of their better resistance to nuisance alarms caused
by steam/invisible cooking particles.


Available in mains, mains with battery or battery configurations.
Ideally install one optical and one ion alarm to provide maximum protection.
Optical, also known asPhotoelectric smoke alarms use an infrared light emitting
diode (LED) as the light source.

See illustration.
When smoke enters the chamber the smoke particles scatter the infrared light.
Some of the scattered light enters the photo detector portion of the sensing
chamber. The smoke alarm electronics detect this scattered light and sounds the alarm.

Heat Alarms:

This is a relatively new product for domestic residences and should always be used in conjunction
with interconnected smoke alarms.
These are fixed point Heat alarms triggered when the ambient temperatures reaches 57 deg C.

The  Building Regulations from 2000, applicable from July 2000 require many new homes to have
them fitted in the kitchen area.
Cooking appliances are the source of most residential fires, but due to steam
and cooking particles, the kitchen is a location, unsuitable for smoke alarms.

The Building Regulations Heat Alarm requirement, applies in England & Wales, N. Ireland & Eire,
but has not neen adopted in Scotland.

Other areas to consider are Garages where exhaust fumes may damage smoke alarms,
but where a considerable amount of flammable material may be stored eg petrol/paraffin/turps/barbecue
fuels/paint/cardboard etc.
Many integral garages are often sited under bedrooms.
Unconverted loft spaces are another area: converted ones should have smoke alarms.

The dust and many temperature changes in a loft space make smoke alarms
unsuitable in this location.

• No single type of alarm is suitable for the whole house

Cost of Ownership:

An alarm with sealed in or rechargeable battery back up will cost more than the types with loose
alkaline batteries. However,  the sealed in models (ending with a product code of "R" or "LL")
are Guaranteed for 10 years. Therefore the additional premium in purchase price is more
than outweighed by not having to buy new batteries every 2 years.
And you have a guarantee for the alarms whole working life of 10 years.
A smoke alarm costs around £1 (€1.45) per annum to run in terms of electricity charges -2007.
 

Using the well proven electrochemical cell technology, Kidde's  range draws on its
US heritage, where it is market leader.
Regularly sampling the air every 15 seconds* to alert you to a dangerous
build of Carbon Monoxide; CO is emitted by all fossil fuels appliances, as a by product of combustion.
* 5 times more frequent atmosphere checking than most CO alarms.
Kidde's unique Smart Interconnect technology allows their hard wired Smoke, Heat & CO alarms to be interconnected.

Available in Hard Wired, plug in, or battery configurations.
(Only Hard Wired have Smart Interconnection).

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