On one hand, municipal warning systems are, just like national warning systems, established to warn against common dangers. On the other hand, considering a smaller area they cover and local conditions, a certain type of danger is often more significant. The relationship between the national and a municipal warning system depends on the legislation of a particular state. In some countries only a national warning system exists, in others only municipal systems are used. Very often, governments only specify technical conditions for municipal warning systems and a method of their central control. As regards their operation a local municipality is held responsible.
In this case, a warning system is usually controlled from a single warning and notification centre, the technology of which is fully backed up. For cities, it is also possible to control this system from individual city districts. Sirens are controlled by radio infrastructure functioning via designated radio channels. POCSAG, GPRS or satellite-based control can be used as a back-up channel. In addition to that, the satellite-based control can also be used as a main control channel. The system activates sirens within a several seconds and its feedback stating the result of individual siren activation is provided within several minutes. It is possible to control the both municipal sirens and sirens of autonomous warning systems operated by industrial public endangering companies. It is possible to control internal evacuation broadcasting systems, broadcasting systems at sports places and municipal broadcasting systems, if these exist. The warning and
notification centre is equipped with VEKTRA software, which, apart from monitoring and control of a siren network, also sufficiently supports processes taking place in the warning centre once an emergency situation is announced.
These are mainly automatic calls of employees in charge to their workplace and informing relevant institutions as specified in emergency plans. The system consists of:
1. A main municipal warning and notification centre.
2. Warning and notification centres of city district (in cities).
3. Radio communication infrastructure (in the case of towns, radio units built in sirens are sufficient).
4. PAVIAN-type electronic sirens.
5. Interfaces for autonomous warning and broadcasting systems.
MAIN MUNICIPAL WARNING AND NOTIFIICATION CENTRE
This consists of a computer equipped with VEKTRA software, a central communication unit for siren radio control and other hardware for a backup communication channel, and for notification and recording. The entire technology is fully backed up and it is capable of controlling all the sirens in a town or a city, and connected autonomous and broadcasting systems. The VEKTRA software continuously checks both the conditions of individual sirens and of a communication channel. Once an emergency situation is announced, the software provides effective support of processes taking place in the centre, especially notification of people and institutions in charge and recording phone and radio communication for later analyses.
CITY DISTRICT WARNING AND NOTIFICATION CENTRES
These also can be equipped with a computer with VEKTRA software installed thus being able to provide the same functionality as the main centre, or with as much as local control units designed to activate sirens in a particular city district, depending on such district competences and size.
A designated radio channel is used as a main communication channel. It is,however, also possible to use satellite control or standard WiFi. It is often sufficient to use radio units built in sirens for a designated radio channel. These units represent standard extension modules of sirens and can turn each siren into a signal booster, which substantially reduces costs of new infrastructure establishment. In the case of cities or extensively divided terrain autonomous radio repeaters or SMART communication units can be used. If WiFi technology is to be used autonomous communication infrastructure must be established, taking into account limited coverage of broadcasters. It is very easy to use satellite-based communication since it only requires the use of a satellite data modem from a relevant service provider installed in each siren. Yet operating costs of such system are quite high. A backup control channel will be used based on local conditions and a
type of a main channel, with which it should not share any common feature.
PAVIAN ELECTRONIC SIRENS
PAVIAN-type electronic sirens can be used as a terminal acoustic feature. These are designed in such a manner that a municipal area would be covered with acoustic signal of a desired acoustic pressure. A populated area and a desired acoustic pressure related to the background noise are, in most states, defined directly by law. When preparing acoustic projects, it is necessary to take into consideration specifics of individual city districts. Acoustic measurements can be, for instance, taken in the time, when acoustic sound is maximized so that the siren signal spill-over would be sufficient. Considering extremely high requirements related to such system reliability, the entire functionality of this type series is used, mainly the auto-testing one.
INTERFACES FOR AUTONOMOUS AND PUBLIC ADDRESS SYSTEMS
In most states the obligation to establish internal fire evacuation PA systems is embodied directly in their legislation. In some legal systems it is also enacted to connect these public address systems with a national or municipal warning system, the purpose of which is to provide external sound distribution. Considering the character of the life in towns and cities and considering sound insulating properties of new buildings it is possible to increase efficiency of warning processes by interconnecting evacuation PA systems and municipal warning systems. Moreover, warning can be more effective by connecting autonomous warning systems of industrial public endangering companies. To connect such systems a TSTG interconnecting unit is used.