Not in all cases. Every home and business in Queensland must have fire detection in one form or another. Keep in mind that if you have sprinklers you may not need detectors since when a sprinkler head is activated it can set the alarm off. Always speak with people qualified in detection since you may be sold a system you don’t need.
Do I need to have my detectors tested and maintained? Yes. All detectors muct be tested every 6 months and records of maintenance kept. Records must be made available for inspection.
What detectors do I need? The type of detector greatly depends on what alarm panel the premises has (if any), what use the premises has, what council class the premises has, and ultimately what a certifier has indicated should be installed.
There are two methods for detecting fire from the presence of heat:
Fixed temperature heat detectors operate when the ambient temperature increases sufficiently to predetermined level where the heat detector will operate
A rate-of-rise heat detector operates when the ambient temperature increases over time equal to or greater than the rate of change the detector was manufactured to operate
Over the years there has been continuous development in the technology to detect heat. These technologies can be broken down into four main types which are: Electromechanical, Optomechanical, Electropneumatic, and Electronic (Thermistor)
What is smoke? Smoke is the collection of airborne solid and liquid particulates and gases emitted when a material undergoes combustion, mixed with the quantity of air that is mixed into the particulate mass.
Smoke particulates are generally grouped in three particle sizes. Depending on particle size, smoke can be visible or invisible to the naked eye.
The five types of smoke detectors
Ionisation smoke detector An Ionization smoke detector consists of the following main components;
a radioactive source, usually Americium-241 that emits alpha particles
a ionization chamber, an air-filled space between two electrodes
The alpha particles pass through the ionization chamber, and permit a small, constant electric current between the electrodes.
Smoke particles that enter the chamber absorbs the alpha particles, which interrupts the electric current, activating an alarm.
Photo-electric smoke detector An photo-electric smoke detector is a scattered light sensor or nephelometer, that consists of the following main components;
a light source
a lens to focus light into a projected beam
a sensor at an angle to the beam as a light sensor
In the absence of smoke, light passes in front of the sensor in a straight line.
When smoke enters the optical chamber across the path of the light beam, some light is scattered by the smoke particles, directing it at the sensor and thus triggering the alarm.
Projected beam smoke detector An projected beam optical smoke detector operates on the principle of light obscuration and comprises;
A projected beam transmitter & lens
A light receiver
A light reflector (not in all cases)
The light transmitter emits an invisible beam of light that is received by a receiver in a normal condition.
The receiver is calibrated to a preset sensitivity level based on a percentage of total obscuration. When smoke obscures the beam, an alarm signal is activated.
Aspirating smoke detectors An aspirating smoke detector is a very sensitive light sensor or nephelometer, that works by actively drawing a sample of air and other contaminates through a pipe network into a sensing chamber and consists of the following main components;
a network of small-bore pipes
a particulate filter
a sensing chamber
a focused light source
a sensitive light receiver
When smoke enters the sensing chamber across the path of the light beam, some light is scattered or obscured by the smoke particles, which is detected by the sensor. The output is analogue and can trigger multiple alarms.
Video smoke detection Video Smoke Detection (VSD) is based on the computer analysis of video images provided by standard video (CCTV) cameras.
A video smoke detection system comprises the following components:
one or more video cameras
software to analyse the video signal
The computer uses specialised software to identify the unique motion and pattern of smoke. This unique signal when identified triggers an alarm.
Carbon Dioxide Alarms
Carbon monoxide alarms are not smoke alarms and do not satisfy the legislation. They may be used in addition to smoke alarms for increased warning.
You can’t see it, taste it, or smell it, but low levels of carbon monoxide can make you sick and high levels can kill. Carbon monoxide is a by-product of combustion. Appliances, such as heaters, ovens, and cooktops which burn gas, oil or wood emit carbon monoxide.
While carbon monoxide alarms are widely used overseas to check the safe operations of central heating systems, they are yet to be commonly used for the detection of fire in the home.
Disadvantages: One disadvantage of carbon monoxide alarms is that they are more expensive than photolectric alarms. The second disadvantage is carbon monoxide alarms only have a lifespan of approximately 5 years.
Carbon monoxide alarms are in addition to a working ionisation or photoelectric smoke alarm. They should not be used as the sole smoke alarm.
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