By Lars van den Heuvel

Verbal instructions, it is now generally agreed, are the most effective way of notifying occupants in a facility of an emergency and instructing them where to go.  To be truly effective, however, the instructions must be transmitted over a voice alarm system capable of maintaining good speech intelligibility over large distances.  And the system must remain operational in harsh conditions as in the event of fire.

A SOLUTION FOR EVERY NEED

Applications for voice alarm systems range from relatively simple configurations in shops and offices to extensive multi-zone installations in, for example, sports stadiums, high-rise buildings, airports and even cruise liners.  All must satisfy two important criteria: guaranteed speech intelligibility and message delivery.  To meet these criteria, safety manufacturers around the world are producing EVAC-compliant voice alarm systems that are also fully functional public address systems.

To meet the diverse range of applications, Bosch, for example, currently offers two solutions.  One is the Plena Voice Alarm System -- a modular PA and voice alarm system primarily for small to medium-sized buildings.  The other is the fully-digital Praesideo Emergency Sound System -- offering virtually limitless multi-zone and networking possibilities and the superior sound quality that only digital audio processing can guarantee.     

VOICE ALARM SYSTEM

The Plena Voice Alarm System provides EVAC-compliant emergency evacuation facilities in all applications where public safety is a major concern, for example schools, hotels, shopping centers and factories.  Designed to meet the stringent IEC 60849 standard for sound systems for emergency purposes, the system offers all essential EVAC functionality -- including system supervision, spare amplifier switching, loudspeaker-line surveillance and digital message management.  A remote-control panel is also available for integrating a fireman’s panel near the main entrance that allows the emergency services to identify the place of the alarm in the facility, take over the automatic evacuation or silence and reset the alarm.  For applications such as hotels and shopping malls, the system also offers facilities for BGM (Background Music), paging and playing pre-recorded commercials.

Easy Expansion

The system is based on a controller with a supervised emergency microphone, a built-in 240 W booster amplifier, digital message manager and message routing for up to six zones (allowing phased evacuation in the event of an emergency).  The controller can be used as a simple stand-alone solution for smaller applications or it can be easily extended to cover up to 60 zones using multiple six-zone routers.  In addition, up to eight call stations and 32 call-station keypads with programmable keys can be connected for message routing.  And, to allow the system to be located in a fire-resistant cabinet or in another secure location, one or two remote-control panels, including remote-control panel extensions, can be incorporated.  Each panel duplicates the controls and indicators on the controller and router front panels, including the emergency microphone.  Offering the latest in plug-and-play functionality, the Plena voice alarm system can easily be installed by anyone familiar with basic public address systems. Elements are interconnected using standard RJ45 connectors and CAT5 cables. The system is configured for specific applications using DIP-switches to set basic functions and a PC for more advanced features.

EMERGENCY SOUND SYSTEM

When it was introduced, the Praesideo PA and Emergency Sound System was an important development, bringing for the first time highly innovative and advanced digital technology to the public address market.  Its digital sound quality guarantees freedom from interference, freedom from signal corruption and very high signal-to-noise ratio.  So messages are just as clear coming out of the system as when they enter -- guaranteeing perfect speech intelligibility and message delivery.  As well as being the first public address and emergency sound system to go fully digital, it was also the first to receive IEC 60849 certification and still is the only system in the world to have independent certification to this standard.  This was awarded by TU‥V, the renowned German quality and safety organization, in April 2003 after three months of intensive testing and included full certification of the Praesideo production process.  The system has also been certified by TU‥V to the BS 5839 standard for fire detection and fire alarm systems.  Besides certification to the voice alarm standard, the system is SOLAS certified for off-shore applications, guaranteeing the system’s reliability even in harsh conditions such as those at sea.  The emergency sound system not only meets but also exceeds the requirements for voice alarm standards.  The recently introduced Multiple Line and Loudspeaker Supervision enhances safety and security by monitoring the correct functioning of individual loudspeakers and loudspeaker line branches.  This unique technology provides for loudspeaker supervision via standard EVAC-compliant 70/100 V loudspeaker lines.  Since no additional cables have to be installed, this results in lower installation costs and easy re-use of existing loudspeaker cabling.  The system’s digital architecture also brings programming power and scalability.  The system is fully programmable and configurable from a PC, providing a high degree of flexibility in terms of zone assignments and numbers, call stations, audio inputs and outputs, control inputs and outputs.

A Networked Approach

Unlike traditional PA systems, the system uses a network configuration rather than having all system elements connected to a central control unit.  The heart of the system is the network controller which stores all control information.  It also provides the Ethernet interface for connection to the PC to enable system configuration as well as diagnostic and logging functions.  Moreover, the network controller also stores the digital audio messages for automatic announcements, monitors all system components and reports any changes in status.  The unit features four audio inputs and four audio outputs, as well as eight control inputs and five control outputs.

The network uses fiber optic cabling to assure high reliability, redundancy and freedom from interference.  The fiber optic cabling carries 28 uncompressed audio channels and control data, so no extra wiring is necessary.  Plastic fiber is used to interconnect nodes that are less than 50 meters apart and glass fiber for distances greater than 50 meters.  A fiber interface is used to convert from plastic to glass fiber or vice versa. 

The system architecture is based on daisy-chaining of the units which allows equipment to be added or removed anywhere in the network without affecting the performance of other units.  This architecture gives real freedom of design and makes the system easily expandable without the need for any additional electronics at the network controller unit.  Smaller systems can be expanded to match changing requirements, for instance creating new zones, and the flexible system architecture allows any type of equipment to be located wherever is most suitable in the building (for example, power amplifiers closer to loudspeakers).

Moreover, by connecting the network ends together, a ‘redundant’ loop is created so any break in the cable has no effect on operation, and if equipment operation is disrupted, automatic switching to spare elements in the system is possible.  Another important feature of this network architecture is that the audio input and output signals are processed in the individual system elements themselves.  This brings a large measure of flexibility as each unit can be individually optimized for its particular surroundings and required functionality, allowing the network controller to concentrate on other activities like routing announcements and playing pre-recorded messages.  This gives a much higher level of system optimization than is possible with centralized signal processing.

INTEGRATED APPROACH TO SAFETY AND SECURITY

Voice alarm systems play a crucial role in guaranteeing fast, safe evacuation in the event of emergencies.  For example, by ensuring phased evacuation in tall buildings to manage the flow of people in emergency stairwells, and instructing people to take luggage with them in bomb alerts but to leave everything behind in the event of fire.  Research also shows that a voice alarm reduces pre-movement time as people sometimes initially interpret a bell or a tone as a false alarm or fire drill, slowing down the evacuation process.

Lars van den Heuvel is Product Market Specialist of Bosch Security Systems.