Smoke Detector Alarms in Adelaide – Part 2
Which Smoke Detector Is Right For Your Home
Part One of this blog described the reasons for having a smoke detector and general upkeep. In Part Two, we discover the different types of detectors available and how they work. I’ll also go into some of the science behind why a house fire is so dangerous.
There are two main types of smoke alarms, photoelectric and ionisation. Through research it has been revealed that photoelectric smoke alarms are more effective at detecting smouldering fires and fires that have started in areas that are not within close proximity to the alarm. An ionisation alarm is more effective detecting flaming fires. Within our houses it is possible for a smouldering and a flaming fire to occur. However the recommendation is still for photoelectric alarms to be installed in a house.
For homes which already have ionisation alarms it is recommended that interconnected photoelectric alarms be added to the installation. When the ionisation alarms reach their 10 year expert they should be replaced with photoelectric alarms.
Smoke Alarm Interconnection
Smoke alarms are now able to be ‘interconnected’. This means smoke alarms positioned around the house have a cable separate to the mains supply cable connected to all of the alarms, providing an interconnection. The benefit of interconnected is that when one alarm detects smoke and activates, all of the alarms in the house will activate their warning sound. This is extremely important to help with early warning and especially assists in houses with children, double story or of a design that limits sound travel. Imagine a smoke alarm sounding upstairs in a house where young children are sleeping, not having an interconnected alarm downstairs could prove to be fatal by time we become aware of the fire.
Photoelectric Smoke Alarms
Photoelectric Smoke Alarms detect larger smoke particles; these are the visible products of combustion. Smouldering fires are the type that produces visible products of combustion. Photoelectric detectors consist of a light sensor made up of an LED light source, lens and a ‘photoelectric’ receiver. In simple terms a change in light being received back to the receiver tells the detector there are particles in the air and the alarm will activate.
Ionisation Smoke Alarms
Ionisation Smoke Alarms detect very small smoke particles. A radioisotope inside produces ionising radiation within an open chamber that allows current to travel between two electrodes. When particles from a fire enter the chamber ions attach to the particles which cannot carry current to the electrodes. The detector senses the change in current and the smoke alarm will activate. So small are the particles that they are considered to be the invisible products of combustion. The type of fire that produces this type of particle is called a flaming fire. Due to this reason an ionisation smoke detector is not recommended for use in areas near kitchens, combustion heaters or open fires.
Multi Sensor Alarms
The multi sensor alarm contains two separate sensing elements, optical and heat. Due to being able to detect both byproducts of fire the multi sensor alarm is excellent in responding to flaming and smouldering fires.
Heat alarms are designed to be used in conjunction with smoke alarms and not as a replacement. They are interconnected with smoke alarms. Heat alarms can be used in kitchens and areas prone to nuisance tripping where the installation of a smoke alarm would not be feasible.
Heat switches exist which can be installed in roof spaces that detect changes in heat and can be interconnected with smoke alarms within the house for early warning of roof space fires. Roof space fires like smouldering fires can ignite and expand silently and without warning.
Smoke Alarms for Impaired Persons
For those who are deaf or hard of hearing, there are smoke alarm systems available that consist of strobe lights and vibrating pads in addition to the audible alert signal.
For people that are movement impaired, a smoke alarm system can be installed that interfaces with communication equipment so that carers and the fire service can be notified.
Power Supply Options
Hard wired – 230V mains supply with conventional 9 volt battery backup
Hard wired – 230V mains supply with 10 year long life lithium battery
Battery Operated – 9 volt battery
Lithium Battery Operated – Sealed unit with non-replaceable and non-serviceable long life battery (approx. 10 years)
Interfaced with Domestic Security – 12 volt with battery backup
Smoke alarms should comply with Australian Standard AS3786 and marked with the standard. At Adelaide Electric we only supply and fit high quality and proven smoke detectors.
The dangers of a Smouldering House Fire.
A Smouldering fire is a flameless form of combustion, characterised by low temperature and sustained by the heat produced from oxygen and a combustion source. There are many materials in our house that can sustain a smouldering fire. Some examples are timber furniture and framework, synthetics and polyurethane foams found in furniture foam and bed mattresses, curtains, carpet, upholstery, clothes etc. These materials also act as insulation in order to reduce heat loss and maintain the smouldering reaction. Household fires of the smouldering type do not require a strong heat source to start. Too often we hear of a candle or cigarette left unattended or an electrical circuit fault resulting in a house fire. We can see that the hazard posed is that these fires can be easily initiated by a heat source that would normally be too weak to ignite flames and therefore also difficult to detect. A characteristic of the smouldering fire is also its ability to spread slowly and silently while producing large amounts of toxic gases until the right conditions occur and a large flame fire erupts.
We learned earlier that smouldering fires produce toxic gases, but they also produce these toxic gases at a faster rate than a flaming fire and leave behind large amounts of residue that contributes to property damage. Unfortunately that’s not all, the gases produced can also be later ignited and produce a flaming fire.
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