Developments in Voice-based Alarm Technology

In the early years of fire alarm systems, the sound produced by an electrical motorised bell was the most recognised fire alarm alert signal. Electronic sounders then became more popular due to improved operational characteristics, in particular lower current consumption and greater user control. Electronically generated tones were used to warn that the fire alarm system had been activated and the building should be evacuated. There are now numerous different tones available and therefore we are faced with most countries choosing their own individual tone, thus resulting in no single standard fire alarm tone across the industry.

It has been demonstrated that voice and spoken instructions greatly reduce the time taken to evacuate a building after the fire alarm has been activated. Any alarm can cause members of the public to panic, however a voice instruction relayed in a calm and succinct manner can reassure the public and give clear and precise instructions. This would include large office buildings, superstores and other public attractions with a regular occurrence of visitors who would be unaware of the fire and emergency procedures. Specific voice messages can also be relayed to members of staff or other personnel, resulting in voice being intrinsically more effective than an alarm tone.

We should also take into consideration the increase in the variety of sounds within industrial buildings, such as water/gas leakage alerts, machinery shutdown and other general warning sounds. This makes it difficult for personnel to differentiate the fire alarm alert tone from these other sounds and therefore the reaction time to respond appropriately would be significantly delayed. A voice system could be set up to automatically output the correct message to appropriate staff and instruct them on how to proceed.

The evacuation procedure in large public buildings can often be very complicated. This is made worse with multiple fire exits and indiscriminate signage, creating panic and disarray as hundreds of people attempt to evacuate the building. An advantage with a voice-based alarm system, in this situation, is the ability to set up different messages that are appropriate for different areas within a building. For instance, in the event of an alarm they are automatically able to instruct people to the nearest exit quickly and without confusion to enable a safe and timely exit. Additional instructions could be added to the message such as “Do not use the lifts”.

Voice Alarm (VA) Systems versus Voice Enhanced Sounders.

At this point, it is important to distinguish between two different approaches to applying voice to fire detection and alarm systems.

A voice alarm (VA) System is a specifically designed sound distribution system that broadcasts voice messages. It is normally connected to alarm outputs from the fire detection system with dedicated control units/equipment, amplifiers, microphone options and loudspeakers. A voice enhanced sounder is an individual electronic sounder that is specifically designed for voice messages and is connected directly to the alarm output or to the detection loop of the fire control and indicating panel.

It is important to recognise the difference between voice enhanced sounders and VA systems in terms of their applications and practicalities. In large places of assembly such as train stations, airports and shopping centres it is often the case that a VA system is installed to give additional public announcements such as flight arrivals or specific information. It is then more appropriate to utilise the same system in the event of an emergency to continuously update the occupants of the building as to the situation and instructions on how to proceed. Alternatively, this type of system could be used to broadcast subtle or ‘coded’ messages from the announcer to members of staff, alerting them to a situation and also by the emergency services to aid the evacuation. Many airports and other large public buildings implement public address (PA) and voice alarm (VA) hybrid systems providing the ability to communicate to any member of staff or the public depending on the circumstance.

Voice enhanced sounders are used as an alarm device that is directly connected to the alarm circuit of a fire detection system. They are normally standalone units which automatically play a voice message when the system operates and hence are generally easier to install. Voice enhanced sounders can be used in a wide variety of different applications from the small shops and offices right up to large buildings and complexes.

VA systems and voice enhanced sounder systems can vary significantly in price. VA systems tend to be more complicated by having networks of loudspeakers, microphones and all manner of sophisticated communications equipment, whereas voice enhanced sounders are connected directly to the fire control and indicating panel. The difference here is that the cost of a voice enhanced sounder system can be more cost competitive than a VA system. For fire safety integrity reasons, both a VA system and a voice enhanced sounder system should be fitted using fire resistant cabling.

Standards.

In recent years standards have been developed and improved for both voice sounders and voice alarm systems.

The European standard EN54-3 “Fire Alarm devices – Sounders” was extended in 2006 to include voice enhanced sounders, to encourage the development of higher quality voice sounders. This has subsequently increased their prevalence within the industry. In 2008 two standards were published, EN54-16 “Voice alarm control and indicating equipment (VACIE)” and EN54-24 “Components of voice alarm systems – Loudspeakers”. At ISO level, the equivalent ISO 7240-16 for “Sound Systems Control and Indicating Equipment” and ISO 7240-24 for “Sound Systems Loudspeakers” have also been developed.

In addition, national codes of practice have been revised to follow technology and application of VA systems. One such example is BS5839-8:2008 “Code of Practice for the design, installation, commissioning and maintenance of Voice Alarm systems”. In this 2008 revision, it also recognises the role of voice enhanced sounders in a VA system. By setting new standards for the product and its installation, designers have been able to implement them into their systems with more confidence due to their qualified safety, efficiency and intelligibility measures. Many voice sounders can be seen in the marketplace today and have proved particularly successful in many applications in the UK and around the world.

As well as this, the system designer must consider disability discrimination legislation, making sure that there are sufficient visual and sound alarm devices that warn the hard of hearing and visually impaired that an alarm is in operation. For this purpose, voice enhanced sounders can incorporate a visual alarm indication in one combined device.

In the support of changes to standards and applications, new courses led by the Fire Industry Association (FIA) in the UK are already addressing this with a new training module on voice alarm systems. This course will offer training on the important aspects of voice-based alarm systems such as interface training between FACIE/VACIE, creating a voice system design plan to assist synchronisation and much more.

Technology.

Technology has made a significant impact, by enabling the combination of voice-based alarm systems with other systems, resulting in a seamless level of building integration and networking.

System speech intelligibility has also made large strides forward with improvements to the components within a VA system. Continuous developments in electronic technology reduces the cost of increasingly more powerful microcontroller IC’s with digital signal processing capabilities, ideal for generating good quality voice messages. Memory storage components continue to get physically smaller and cheaper while increasing in storage capacity, allowing multiple higher quality audio files to be stored within a single voice sounder. Customers may choose from a wide range of standard sounds, tones and voice messages in different languages.

Most manufacturers also offer the option for bespoke messages, allowing a customer to create their own audio files to be uploaded into their voice sounders. This may be programmed during production, or depending on the product, the customer may be able to manually uploaded their own messages from a PC (similar to storing audio files in consumer devices such as MP3 players), or transfer them via a small memory card.

In certain situations, greater control is required over the voice sounder system than simply switching power on and off to the alarm circuit. For instance a tourist attraction, such as a museum, may have occupants of multiple nationalities with differing native languages. It has been speculated as to whether it is appropriate to install a voice system whereby some of the public may not be able to understand the language the message is broadcast in. This would hinder their ability to understand the nature of the alarm, causing unnecessary panic or confusion.

By contrast, a tone alarm sounds the same in every ‘language’. However, some manufacturers now offer control units which can transmit sequential messages through a networked system, for example, broadcasting an English message followed by a French message, with a tone separating them. Such systems may also transmit specific messages to targeted voice sounders that are appropriate for the type of alert.

Where synchronicity between voice sounders is concerned, these control units are able to keep them sounding at exactly the same time – important for intelligibility reasons. For example, large open buildings are likely to reverberate and echo and therefore the intelligibility of a voice sounder will deteriorate over distance, making it especially important for multiple voice sounders in the same space to be kept in synchronisation.

The standard EN54-3 for “Alarm devices – sounders” in Annex C, requires any system that offers a method of synchronisation, to ensure that sounders within 20 metres of each other must remain in synchronisation after 30 minutes of the alarm being activated, with a delay between sounders of no more than 0.02 seconds.

As mentioned briefly, a key concern regarding any voice sounder system is reviewing how intelligible the voice messages are once the sounders have been installed into a location. Factors such as the audio quality of the sound file, the quality of the transducer in the sounder unit, the acoustics of the sounder body, the shape of the room in which the sounder is installed, any background noise present during the time of an emergency, and a system’s synchronicity all affect the intelligibility of the voice message.

These are all considerations that must be made by the designer, when planning out the system, but actually measuring the effectiveness of the system can be difficult. However, over the past few years intelligibility measurement techniques have been developed which can make this reviewing process much simpler.

Using STI (Speech Transmission Index) and CIS (Common Intelligibility Scale) measurements, the designer and the installer can confirm that the system they have created has met standards. A CIS level of 0.7 or an STI level of 0.5 (corresponds to comprehension of approximately 80 percent of words and 95 percent of sentences) must be attained. Methods of measuring this will not be discussed here.

Combined, these developments have improved the flexibility of design and the intelligibility of a voice enhanced sounder system immensely.

Conclusion.

As in all cases of technology there are challenges to ensure that the voice message has the correct information for the application, that it is intelligible and most importantly that it is effective enough to ensure that it can instruct and evacuate people safely in the case of an emergency situation. In addition, there are increasing demands placed upon on building safety and efficient evacuation procedures in life critical applications.

With the introduction of robust new and revised standards and applications for voice-based alarm systems, this provides solid guidelines for both designers and installers to work to. Combined with technological advancements, the intelligence and flexibility of voice enhanced alarm sounder systems has remarkably increased while also reducing the overall system cost. As a result, voice enhanced sounders and VA systems are fast becoming the more popular choice.

Contact: For further information, go to www.cranfordcontrols.com

(Author)

Neil Young is Senior Technical and Engineering Manager at Cranford Controls