Point/Spot Detection

Point or Spot smoke detection refers to a conventional/addressable detector commonly made of a plastic shell encasing a sensor within. These detectors use light obscuration over a distance between the emitter and receiver. Normal conditions would have an unobscured light path between the emitter and receiver componentry, however, when smoke passes this path, it reduces the light to the receiver which would normally activate a condition at around 0.03 to 0.05% light obscuration over 1m.

These detectors are often strategically located within a given area with each sensor covering a specific square area (m2) depending on various ambient conditions. By utilising light obscuration technology, this reduces the detectors ability to detect smoke at incipient stages of fire, specifically slow smouldering fires that can occur in wiring or other applications which can smoulder for hours before combustion begins.

Point detectors also require regular maintenance, which can also add to detection degradation over time due to the maintenance process. Maintenance procedures require the engineer to use smoke in a can which if incorrectly used can coat the optical lenses of both emitter and receiver.

It is also a recommendation to replace a point detector sensor every 10 years due to this testing procedure and also ambient conditions which are ever present without filtration around the optics of the detector.

Even with regular maintenance, point detectors can be prone to false alarms, specifically from moisture, and struggle to detect smoke in environments with high air flow. This is not ideal for cold or air-conditioned environments such as data centres full of server racks or large warehouses using powerful HVAC equipment to circulate cool air around the environment. Point detection becomes particularly difficult to use when hot and cold aisle arrangements are used.

Air Sampling Alternative to Point Smoke Detection

The alternative to point smoke detection is the aspirating smoke detection system, which uses simple air sampling points located at various intervals on an aspirating pipe network. The locations of these sample point holes (equivalent to a detector) would be in the same location as a point detector and the same design standards would be applied when designing the sampling system as you would if using a point detection system.

The advantage of air sampling systems is that it constantly monitors the air from the protected environment. Sampling holes do not sense smoke independently, however, a collective collaboration between them always exists as they share the same pipe network and the same detector.

Detection of smoke is achieved by means of revolutionary flair detection technology using a short wavelength laser. As the air passes through the detector’s chamber, emitted light from the laser will reflect off the surface of smoke particles in the air mix. The sensing components then measure this reflective light to provide accurate data to the processor. With up to 40,000 events recorded, visualisation of the smoke can be used to generate a smoke trend graph using the detector’s PC interface and software.

Smoke thresholds can be set at desired levels to provide up to four different levels of alarm, such as Alert, Action, Fire 1 and Fire 2. With this flexibility, sensitivity can be set to meet the environmental challenges.

In addition to the smoke sensing capabilities, air sampling systems can also provide detailed logs of faults for easier maintenance or fault finding, such as: system faults, high and low airflow, detector and component failures, power supply faults whilst continually recording smoke level changes along with alarm triggers.

Maintaining an air sampling system is where the real advantages come in. Instead of testing each point detector, air sampling systems use measured testing techniques suited to the type of environment they are protecting. For example, if an air sampling system was installed in a data centre or telephone exchange, a hot wire test would be used. This test uses a measured section of insulated cable which is heated for a defined period, this will produce a known quantity of smoke. The detector will then record the smoke changes over this defined time period and the thresholds can then be set to suit the desired sensitivity requirement for each alarm level.

If an air sampling system was installed within a warehouse, the detector would be located at accessible level, maintenance is carried out at ground level along with the testing procedures. There is no need to use access equipment to get to each point detector reducing inconvenience to business operations. Faults can only occur at low level which simplifies the fault-finding processes.

The pipe network is also easily cleaned using blow through technology, which will keep all pipe and sampling points clear from blockages.