Aspirating smoke detectors.
Aspirating smoke detectors are complex active fire detection devices that allow you to issue a reliable warning or alarm signal at the earliest stages of the occurrence of signs of a fire.
Aspiration fire smoke detectors consist of a detector unit with an aspirator and a system of pipelines with air sampling openings through which air samples from the controlled space are delivered to the detection device (Fig. 1).
This detector design allows for maximum isolation of the measuring chamber from external influences.
High sensitivity, which in some models reaches values of 0.0015%/m (0.000065 dB/m), is many times greater than the parameters of point detectors and is achieved through the use of ultra-sensitive optical density meters.
Aspiration detectors are used to monitor not only premises, but also equipment, air conditioning units and air ducts.
The use of aspiration detectors ensures the highest level of fire protection for any facility, and the specific design and additional devices allow them to be used even where the use of other types of detectors would be ineffective or simply impossible.
At present, technical requirements for aspiration detectors are established in GOST R 53325-2009 «Fire-fighting equipment. Technical means of fire automation. General technical requirements. Test methods».
In this article, we will not dwell on technical characteristics, but will consider possible areas of application and advantages of installing aspiration detectors on various types of objects.
In Russia, the main requirements for the design and installation of aspiration fire detectors are defined by the Code of Practice SP 5.13130.2009 «Fire protection systems. Automatic fire alarm and fire extinguishing systems. Norms and rules for design.»
And here the first point is the recommendation to install aspiration detectors to protect large open spaces.
Such premises include atriums, production workshops, warehouses, retail spaces, passenger terminals, sports halls, stadiums, etc.
According to clause 13.9.1, class A aspiration detectors can be installed in rooms up to 21 m high, class B – up to 15 m, class C – up to 8 m.
In the case of using aspiration detectors in a room over 12 m high, unlike linear smoke detectors, there is no need to install a second tier of detectors.
Building structures usually impose certain restrictions on the installation locations of linear smoke detectors in such premises, forcing them to be mounted at some distance from the ceiling, which in turn seriously reduces the level of fire protection of the premises and the facility as a whole. Aspiration detectors do not have these disadvantages.
A pipeline with air intake openings can pass directly under the ceiling, bend around obstacles, thereby expanding the monitored area and reducing the likelihood of false alarms.
|
Fig. 1.Aspiration detector |
 |
Moreover, in accordance with SP 5, it is allowed to embed air intake pipes in building structures and finishing elements. This application option allows you to protect premises with high design requirements, such as historical buildings, museums, premises with a large glazing area, etc. Moreover, the elements of the fire alarm system in this case are truly invisible, and the level of fire protection remains at the highest level.
Air intake pipes can be laid both horizontally and vertically, which allows you to determine the optimal access option to the detector for maintenance and repair at the design stage of the system and place it in the most convenient place for this.
Let's assume that it is necessary to monitor limited, hard-to-reach spaces, such as the space behind a suspended ceiling and under a false floor, a cable channel, the internal space of units and mechanisms, such as escalators or conveyor lines. And here, according to SP 5, the use of aspiration fire detectors is allowed.
It is possible to monitor both the main and the dedicated space of the room, i.e. in case of monitoring the ceiling space, the pipes of the aspiration detector are located behind the suspended ceiling, and additional capillary tubes lead the air intake openings into the main space. Particular attention should be paid to the issue of protecting expensive equipment and material assets.
The use of highly sensitive aspiration detectors when protecting, for example, servers or data arrays, allows you to record even the overheating of individual components of an electronic device.
The advantage of aspirating detectors is that a pipe or capillary branch with an air sampling hole is connected directly to the protected object.
Figure 3 shows an example of protecting cabinets with equipment.
Server rooms, data centers, warehouses with rack storage and other objects where it is extremely important to detect and eliminate the source of fire at the earliest stage to prevent major damage are equipped in the same way.
|
Fig. 2. Example of a room monitored by aspiration detectors |
 |
There are often objects whose monitoring by traditional methods is complicated by difficult conditions, such as dust, dirt, extreme temperatures, high humidity, electromagnetic interference, high air flow rates, etc.
The use of aspiration detectors here is also an effective method of protection.
Since air samples are taken from the monitored volumes through small openings, air flows from ventilation and air conditioning systems do not affect the detection ability.
That is why it is possible to place the air sampling pipes of the aspiration detector directly in the air ducts and on the air intake grilles.
If operating conditions are associated with significant pollution or dust, then external filters are additionally installed in the pipeline system (Fig. 4).
Protecting the measuring chamber of the device from foreign particles reduces the likelihood of false alarms and extends the service life of the system.
In the most severe conditions, for example, at waste processing plants or in industrial production, additional provision is made for blowing the pipeline in the opposite direction.
For this purpose, a valve is installed that, when blowing, cuts off part of the pipe before the detector unit, after which the contaminants are blown out of the pipeline.
And in some cases, when blockages in pipes can occur too often, it may be advisable to implement automatic cleaning of the pipe system.
| Fig. 3. Arrangement of pipes when protecting cabinets with equipment |
 |
| Fig. 4. Three-level replaceable filter for air purification |
 |
|
Fig. 5. Condensate extraction device (FAS*ASD*WS) |
 |
|
Fig. 6. Example of a pipeline with a condensate protection device |
 |
When monitoring zones with changing temperatures or incoming fresh air, condensation may form in the aspiration system, which may impair the performance of the detector unit.
However, there is a solution for this case too.
The pipeline in areas with high humidity
is equipped with an additional device for collecting condensate (Fig. 5).
In addition to protecting the detector unit from moisture, such devices can have a filter for additional protection from solid particles. It is installed at the lowest point of the pipeline (Fig. 6). And additional 45° pipe bends allow access to it during maintenance.
The solution described above is used in areas with temperatures from 0° to 50° C. However, the operating temperature range for aspiration detectors is much wider and allows them to be used even at subzero temperatures in deep-freeze warehouses.
The detector unit itself, depending on the optical density meter used, can operate at temperatures from *20° C to +60° C.
When installing aspiration systems, halogen-free plastic pipes are usually used.
PVC pipes can be used at temperatures from 0° to 60° C.
ABS plastic pipes can be used in the range from *40° to +80° C.
And yet, the detector unit is most often taken outside the zone with difficult conditions.
This further expands the areas of application of this type of detectors.
Let's consider another example. Agree, it is quite difficult to find a suitable detector for protecting a sauna.
Some models of aspiration detectors can perform their detection functions at air sample temperatures of up to 110° C.
Of course, plastic pipes are no longer suitable for this example, and in order to eliminate false alarms, it is essential to use a condensate extraction device.
There are several other areas of application associated with the possibility of moving the detector unit outside the controlled area.
Plastic pipes are not conductors and are not subject to
electromagnetic interference.
Such a system can be used even in conditions of increased radiation. In turn, the remote block of the aspiration detector does not create interference in the controlled area, which is very important for diagnostic and testing laboratories.
Many people mistakenly believe that the absence of loop conductors in the controlled area will allow the use of aspiration detectors at explosive facilities in a similar way.
Such a solution does exist, but the situation is somewhat more complicated.
In this case, it is not air that enters the measuring chamber, but an explosive gaseous mixture, and the detector unit itself, at certain values of its composition, concentration, temperature and pressure, can become a source of ignition.
To prevent the spread of flame along the pipeline and detonation in the explosive zone, special explosion-proof barriers are used in the system (Fig. 7).
 |
| Fig. 7. Explosion-proof barrier for aspirating smoke detector |
As we can see, the capabilities of aspirating smoke detectors are wide and varied.
The properties of aspirating smoke detectors, compared to traditional point and other types of detectors, are unique: high sensitivity for early detection, the ability to install in large spaces, the ability to work in difficult conditions, and ease of maintenance even in hard-to-reach places.
Undoubtedly, the regulatory framework created in 2009 will allow aspirating systems to occupy their niche in the Russian market of fire detectors and increase the level of fire safety of many facilities.
T. Sulim
Head of Fire Alarm Systems Department
«Robert Bosch»
Source: magazine «Algorithm of Security No. 1 2010»