Linear fire systems for difficult working conditions.

Linear fire systems for difficult working conditions..

Ackerman Ilya Lazarevich

LINEAR FIRE SYSTEMS FOR DIFFICULT WORKING CONDITIONS.

Source: «Special Equipment» magazine

Statement of the problem.

The main range of tasks usually facing a security systems specialist is, in most cases, quite uniform. Of course, there are no two absolutely identical objects, but the applied approach to ensuring a particular level of security is approximately the same for all cases and, in principle, lends itself to some general algorithmization.

For example, for a specialist in fire alarm systems, there are a number of key factors that determine the quantity, type and composition of equipment included in the project.

These factors include regulatory documents that define the basic standards and rules for fire systems, the structure of the building and premises, the purpose of the premises, etc. As a rule, for each specific case (for example, for each type of premises), the specialist has ready-made technical solutions, by combining which the project as a whole is determined.

It should be noted that almost every designer prefers to work with equipment that he is accustomed to and that he knows well (which is quite natural). However, every specialist from time to time has to deal with non-standard tasks that cannot be solved using standard equipment.

I will give just a few examples of such tasks:

• How to equip a fire alarm system in an architectural monument with a unique interior, where the possibility of laying cable wiring is practically non-existent, and the installation of fire detectors is out of the question, since they do not fit into ceilings with rich painting or stucco?
• How to ensure fire detection in rooms where the temperature range differs significantly from the operating temperature range of standard detectors (for example, unheated rooms, freezers, saunas)?
• How to ensure fire protection of transformer substations or scientific laboratories, where the electromagnetic background significantly exceeds the noise immunity threshold of detectors?
• How to make a fire alarm in correctional institutions, where there is a high risk of deliberate damage to the system?

A simple and elegant solution to these and other complex issues is offered by the Swiss company Securitron. Below we will consider the design features of the system, and then its use in the above examples.

RAS series active smoke detection systems.

Structurally, the system consists of two main parts — the measuring unit and the air duct.

The measuring unit housing contains a blower fan, smoke detectors (1 or 2 depending on the modification), resulting and output circuits.

The unit is installed in dry, heated rooms, usually outside the controlled area and is essentially the only serviced part of the system.

The air duct consists of plastic tubes (rigid or flexible) with air intake points, which are made both in the form of holes in the air duct and in the form of cone-shaped bowls placed directly above the controlled areas.

Fig. 2.

The air duct can have several configurations, with the diameter of the air sampling points changing depending on the distance to the measuring unit, as shown in the diagram. The maximum distance between the last point and the measuring unit should not exceed 60 m. Each air sampling point controls an area of ​​50 m2 (a circle with a radius of 4 m), and the total area controlled by one system is 600 m2.

If one RAS unit controls several separate rooms, each of them must have at least two air sampling points.

The measuring unit, in addition to the air composition, also monitors the serviceability of the blower fan, the constancy of the air flow passing through the unit (with the ability to determine both the blockage of the air intake point or air duct, and leaks from the air duct), the serviceability of the smoke detectors installed in the unit.

The resulting circuits of the device can be flexibly configured to certain response thresholds, with the ability to issue fire alarm signals and preliminary warnings. The PSU 53 analog processing unit (used together with RAS 53) can also be used as an additional device.

This device has 10 stages of air sample analysis with programmable outputs and allows automatic implementation of specified measures (for example, switching off any devices or connecting backup units) before generating a fire alarm signal.

Another additional device — TAR 54 (used together with RAS 54) also allows for temperature control of air at each air sampling point.

Below is a table of modifications of Securitron active smoke detection systems and their main features:

Solution of the problem.

After the theoretical introduction, it is time to move on to the practical application of the RAS series systems using the examples described in the “Problem Statement” section.

1. Architectural monument.

As mentioned earlier, in this case it is very difficult to find a balance between the required level of protection and the required level of aesthetics.

A standard detector, even painted to match the ceiling, still looks like an alien element. The wiring of the loops and their subsequent maintenance also cause problems.

As an option, you can use wireless fire detectors with an autonomous power supply that transmit an alarm signal via a radio channel, but such detectors are even more difficult to fit into an old interior due to their rather large dimensions.

Fig. 3.

Installing the RAS air ducts certainly also creates certain problems, but once they are installed, the fire alarm problem can be considered solved.

Fig. 3 shows only some of the air duct installation options.

Considering the fact that this system is active, the designer is not limited to the ceiling space for installing the system components — the air ducts can also be located in the floor. In this case, measures will be required to prevent clogging of the air intake points.

The measuring units are located outside the front rooms — in utility and service rooms.

2. Rooms with a harsh climate.

Standard point detectors have strict limitations on the operating temperature range. As a rule, at temperatures above 60° C, manufacturers do not guarantee trouble-free operation of the sensor's electronic circuits, and at temperatures below -30° C (especially with intense air movement), ice forms on the detector body, which causes blocking of the measuring chamber and makes the detector useless. Nevertheless, fire safety issues must be addressed even under the described conditions. The greatest risk in this case is posed by production equipment associated with high temperatures, for example, various types of drying chambers, the temperature inside which can reach 200° C.

Fig. 4

Fig. 4 shows a diagram of how to solve this problem using the RAS series system.

It should be noted that in this case a number of problems arise, which in principle can be solved. The first is that the RAS measuring unit uses standard detectors, the air temperature for which should not exceed 60° C.

Laying the air duct through the cooler allows you to lower the air temperature to the required limits.

The second problem arises immediately after solving the first — condensation, which inevitably forms during cooling.

Condensate should be drained through moisture collectors, and the inlet air duct should be connected to the measuring unit not from above as usual, but from below, so that the condensate flows into the air duct, and not onto the electrical parts of the measuring unit.

The air ducts themselves should be made of a material that meets the temperature conditions. Copper is usually used, and alloy steel is used for aggressive environments.

The ideology of using the RAS system at low temperatures, such as freezers and refrigerated warehouses, is similar to the one described above, but low temperatures cause only one additional problem: ice formation at air intake points.

Fig. 5.

In this case, the RAS 52 system provides for the installation of simple heaters. The heaters are controlled by the air flow control system and are automatically switched on when a blocked opening is detected.

When the flow rate is restored, the heating is switched off.

As a rule, only air intake points located in areas of intense air movement or temperature differences (for example, in the door area) are equipped with heating devices.

Fig. 6.

When mentioning warehouses, one cannot ignore high storage facilities with multi-tiered racks.

The RAS system, installed directly on the vertical rack posts, fits organically into the logic of organizing such a warehouse and ensures the detection of a fire at the earliest stages.

If the purpose of the warehouse is constantly changing, or if heterogeneous materials are stored there, RAS 54 systems with mixed optical-ionization detection technology are used to increase reliability.

3. Other complex conditions.

After the above examples, there is little point in dwelling on all the tasks set at the beginning of this article. It is enough to note that there are practically no difficult operating conditions for RAS series devices, since their data collection systems (air ducts) are little exposed to harmful external influences and do not require maintenance, and for the data processing system (measuring unit), as well as for the standard control panel, there is a place for installation at any facility where the necessary climatic and operating conditions are met.

Nevertheless, there are a number of examples in which the use of RAS systems is unacceptable for one reason or another:

• transport tunnels and indoor parking lots — in these places the air may have a high smoke content, which leads to false alarms of the smoke detectors of the measuring unit;
• objects (for example, fuel storage facilities) located outdoors — in conditions of unlimited controlled volume, rarefaction of smoke impurities in the air occurs, and the sensitivity of the system as a whole decreases;
• explosive zones — due to design features, the RAS series equipment is unsafe in these conditions.

For these purposes, Securitron has developed linear thermal differential detector TRANSAFE ADW 511

The physical principle of the detector is based on the change in gas volume when its temperature changes.

Fig. 7.

The device consists of a sealed copper sensor tube (1), the maximum length of which is 80 m, and a measuring unit (2). Under normal conditions, the air pressure in the tube is equal to the pressure in the measuring unit housing. If the measuring tube heats up, the pressure in it increases, which activates the membrane and the alarm contact (3). If there is a slow increase in temperature due to a change in environmental conditions, the pressure drop does not cause false alarms, since it is compensated by the capillary system (4). The electronic unit (5) processes incoming signals and provides signal outputs of the detector. The system periodically performs automatic self-testing. The pressure drop is artificially caused by a piston driven by an electric motor (6). If a malfunction is detected, the detector output “Malfunction” is activated.

The simplicity of the design, combined with high reliability of detection and protection from harmful environmental influences, allows the use of TRANSAFE ADW 511 detectors at chemical and mining industry facilities, paint shops, cooling towers, railway depots, indoor garages, gas storage facilities, transport tunnels, bakeries, etc.

In conclusion, I would like to mention some of the facilities where Securitron linear systems are installed.

The list below speaks for itself:

RAS Series:

• Sanssouci Palace, Potsdam (Germany)
• Opera House, Zurich (Switzerland)
• Madrid City Museum (Spain)
• Jesuit Church, Lucerne (Switzerland)
• Daimler Benz Plant, Sindelfingen (Germany)
• BMW Plant, Munich (Germany)
• Fiat Plants, Turin and Naples (Italy)
• Toyota Warehouses, Vienna (Austria)
• CERN Proton Beam Accelerator (Switzerland — France)
• Bayer Plant, Leverkusen (Germany)
• Lufthansa Hangars, Frankfurt (Germany)

TRANSAFE ADW 511

• Bayer Plants, Leverkusen, Dormagen (Germany)
• Porsche plant, Stuttgart (Germany)
• Hoechst AG plant, Frankfurt (Germany)
• Federal Parliament building, Bonn (Germany)
• Siemens plant, Frankfurt (Germany)
• Conica plant, Schaffhausen (Switzerland)
• Seelisberg tunnel (Switzerland) — 2 lines of 9.25 km
• Arlberg tunnel (Austria) — 13.9 km
• Mont Blanc tunnel (Italian part) — 6 km
• Shanghai tunnel (China) — 2 lines of 2.2 km