Aspirating smoke detector

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An aspirating smoke detector (abbreviation: ARM; obsolete smoke aspiration system or RAS ) is a fire alarm system and can replace an arrangement of several point smoke alarms in a fire alarm system . The requirements for ARM are defined in the DIN EN 54-20 standard and subdivide these into three classes (A, B and C).

Evaluation unit of an aspirating smoke detector

Working principle

An ARM consists of a simple pipe system and an evaluation unit. Suction openings are made in the pipe system and a defined diameter is achieved with suction reducing foils (or clamps). Depending on requirements, air filters, condensate separators or magnetic filters (for metallurgical dust) can be installed between the pipe system and the detection unit. A fan integrated in the evaluation unit continuously sucks in air through the pipe system from the monitoring area. Each suction opening can be viewed as a point-shaped smoke detector. The evaluation unit consists of the actual detection unit and a monitoring of the ARM and the air flow for possible disturbance variables, such as a reduction in the air flow due to dirty filters.

The air samples are fed to the detection unit, where they are examined for smoke particles using built-in fire alarms or sensors. As a rule, particularly highly sensitive optical smoke detectors are used as detectors in order to compensate for the dilution of the smoke caused by the air sucked in from smoke-free rooms. The sensitivity of a measuring chamber is given in light opacity (attenuation) per meter (a light opacity of 0.005 to 20% is not uncommon). These systems can be optimally adapted to the ambient conditions. The detection unit has its own fault detection which, among other things, monitors the degree of contamination. Therefore, ARMs often have two different zone numbers .

Depending on the manufacturer of the evaluation unit, a pipe system with a total length of up to 180 meters can be connected. This corresponds to a monitorable area of ​​up to 2,160 m², depending on the area and height of the room. If the pipe system is installed in a false ceiling, only a few centimeters in size, flat ceiling ducts are visible for room monitoring, the actual suction openings are only a few millimeters in size. This option is particularly interesting for cultural goods and IT.

With smoke aspiration systems it should be noted that only one fire alarm is generated per evaluation unit. The assignment of a special area (with the exception of systems from Hekatron) of the monitored room, e.g. B. to a specific control cabinet is not possible due to the system. An ARM may therefore monitor a maximum of one fire compartment. There is, however, the product-specific option of blowing out the detection tube after the first alarm has been recognized. The RAS then draws in again and determines the time until smoke is measured again at the sensor. With this method, a limited number of suction points can be individually detected and evaluated.

In the case of fire alarm systems, RAS systems simplify maintenance, as only the detection unit needs to be checked. The pipe system is separated from the evaluation unit and the non-return valve by means of a valve and blown out with compressed air . There are also automatic blow-out devices that clean the system at specific time intervals. In contrast, point detectors have to be checked individually, sometimes only with considerable expenditure of time and therefore costs. Depending on the structural conditions, the test is sometimes associated with an interruption in operations. The maintainability is usually offset by the significantly higher acquisition and installation costs and filter replacement (once a year) compared to point detectors. Therefore, these systems are mainly used in areas that are difficult to access or where point-shaped smoke detectors disturb the image of the room.

Areas of application

Possible areas of application for smoke aspiration systems are:

literature

  • Siemens AG (Ed.): Fire protection guide. Technical fire protection and fire protection systems, 2nd edition, Erlangen 2013, ISBN 978-3-89578-429-3 .
  • Hans-Joachim Gressmann: Defensive and technical fire protection. 5th revised edition, expert Verlag, Tübingen 2019, ISBN 978-3-8169-3460-8 .

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