Alarm Technology - Ring any bells?

Early alarm devices were largely electromechanical, being based on electrical solenoids or motors to create an audible signal, so the range of bells, vibrating horns and sirens available was wide and varied. Though undoubtedly effective, these products were not efficient and often required mechanical adjustment during installation to obtain optimum performance. The “alarm bell” is of course still widely used and alarm product suppliers are able to offer a range of electromechanical alarm bells to suit most needs and applications. Given their long history and unique sound it is evident that the general public still associates a bell with a fire warning despite the widespread use of electronic sounders. The popularity of the bell sound has driven manufacturers to make electronic sounders that replicate the ringing tone of a bell.

Sounders
In the 1960s, solid state electronics became viable for the economic design and production of alarm sounders that generated an alarm tone electronically, although it should be remembered that there must always be a mechanical component to turn the electronic signals into a vibration so that it can be heard.
The first electronic sounders were not the efficient compact units that are produced today, as they were based on public address (PA) loudspeakers housed in steel cabinets. However, the realisation that the rocking armature transducer from a telephone handset could be used as an efficient acoustic driver enabled development of the compact units that we know today. Products like Fulleon’s Roshni Sounder, launched nearly 30 years ago, relies on a transducer that is still recognisable as the unit from a telephone handset, albeit now specifically manufactured and tuned for use in alarm sounders.
Transducers are not the only technology; Piezo elements are also used, which employ materials that change dimensions when a voltage is applied, and so driving the metal plates to vibrate. This allows sounders to be manufactured with even lower power consumption, but at the expense of a more limited frequency range over which they can operate efficiently.
Efficiency is a key attribute for fire alarm sounders; low power consumption is needed to keep standby batteries to manageable sizes and with addressable systems, where power and data share the same cable, it is vital to stop the communications protocols from being corrupted by current noise. Today typical current consumption for transducer-based sounders is around 12mA to 15mA for sound outputs of just over 100dB(A) (measured at one-metre from the sounder). The Piezo based sounders, such as Fulleon’s Symphoni Sounder, commonly found in addressable systems, can achieve a similar output for as little as 3mA to 5mA.
Flexibility is another key virtue of the electronic sounder; it can produce many different sounds and operate over a wide range of supply voltages. Typical fire alarm sounders have up to 32 alarm tones and operate on voltages from 9Vdc to 28Vdc and even up to 60Vdc in some instances. Most will allow for two stages of alarm, so that the sounder can be remotely switched between different alarm tones to indicate different levels of alarm condition.
Although 32 Tones may seem excessive for a sounder, there are so many alarm signals within buildings that distinctive, easily identified alarm tones are needed to allow differentiation between them.

Speech
Sounders are limited in the amount of information they can convey, as an alarm signal is only meaningful if the person hearing it recognises it and understands how to respond. For situations where people may not recognise an alarm signal, such as areas open to the general public, a spoken message is beneficial as it provides a clear warning, while instructing and reassuring those affected by the emergency. It has been shown that the extra information in a spoken message allows people to respond much more quickly than they would to just an alarm tone.
Voice messaging has been used with PA systems for many years; the challenge has been to incorporate the technology into low-powered electronic sounders, as achieved in Fulleon’s Symphoni Voice+ product. These voice sounders are not replacements for emergency public address voice alarm (PAVA) systems, but are complements for situations where live voice is not required, or the area to be covered is small and the cost of a PAVA installation is not justified.
Voice sounders like the Symphoni Voice+ are pre-programmed with a set of alarm tones and voice messages allowing the user to choose the best combination of alarm tone and message for their situation. If circumstances require special messages or specific languages, the sounders can be reprogrammed as required. Voice, despite its benefits, can be difficult to apply in real situations as not only must the message be loud enough to be heard, as with any sounder, but also be intelligible. With voice sounders, presently, there is no objective way of measuring the intelligibility level of an installed sounder; the normal techniques used with PA installations cannot be applied as there is no live audio input.

Light
There is an increasing awareness that sounders need to be supplemented by other forms of alarm in areas where people may be hard of hearing or their hearing is impaired by loud ambient noise or ear defenders. Visual alarms based on incandescent lamps have been used within alarm systems for a long time, but again it was the advent of semiconductor electronics that allowed the familiar flashing beacons (strobes) using xenon flash tubes to prevail. A limitation of visual signals compared to audibles is that, unless bright, they are unlikely to be noticed if they are not in a direct line of sight, whereas sound can be heard whether or not the listener is facing the source.
The Disabilities Discrimination Act (DDA) introduced to the UK in 1995 (now largely replaced by the Equality Act 2010) encouraged the supplementing of audible alarm sounders with visual beacons in certain areas of buildings to warn the hard of hearing. The publishing of European standard EN54-23 in 2010 provided test specifications for beacons, but required much brighter beacons than those used presently, which are often selected for their low power consumption rather than for an effective light output.
Currently, there are no beacons on the market that are specifically designed to meet the requirements of EN54-23 and the challenge for manufacturers is to devise solutions for beacons that meet the requirements of the legislation without taking excessive amounts of power from the alarm system. The existing xenon flash tube technology is effective, but power hungry, however the rapid development of Light Emitting Diode (LED) technology will undoubtedly help to alleviate some of the problems with improved efficacy compared to xenon tubes.
Europe has been accustomed to using red beacons for fire warnings, however with xenon technology a red filter is used to give a red flash, reducing the light output by up to 75 percent. Therefore, to achieve the light output required by EN54-23, the power of the red beacons would have to be considerably increased. By switching to white light, it would enable the full light output of the beacon to then be available.
A concern often voiced about the increasing use of beacons is the potential effect on people suffering with photosensitive epilepsy. The standards for alarm beacons require flash rates of between 0.5Hz and 2Hz (one flash every two seconds to two flashes a second) the lower limit for triggering a photosensitive event is cited as 3Hz so modern beacons complying with EN54-23 should fall below this limit, but if several beacons are in view and not synchronised they could present a composite flash of a higher frequency. Recommendations are that beacons should either be synchronised with each other or should be positioned so that only a single unit can be viewed from any point in an area.

Integration
Integration is now high on the list of desirable features for most alarm products and it is routine to find alarm sounders in combination with a beacon. The installation savings are significant as the contractor is fixing and wiring only a single unit instead of two; the saving is probably greatest in markets such as the UK where the wiring codes of practice are comparatively onerous for fire systems.
Integration can be taken much further so that a single point can encompass a sounder, beacon, multi-function detector and as shown in the picture a wireless communications module and batteries too.
Apart from the installation savings there are also possibilities for enhanced operational features and local data processing within the unit. Higher levels of operational monitoring are also possible, for example there are sounders that are capable of checking their own audible output for correct operation so that the whole of the alarm path is effectively monitored from control panel to sounder.

Legislation
Sounders and beacons are life safety products and therefore have to be reliable under all conditions that they are likely to experience. European fire alarm products fall under the Construction Products Directive (CPD) and therefore have to be third-part tested against the EN54 range of harmonised standards. The following standards apply to sounders and beacons:
• BS EN 54-3:2001, Fire detection and fire alarm systems. Fire alarm devices. Sounders. (Voice sounders are covered in Annex C)
• BS EN 54-23:2010, Fire detection and fire alarm systems. Fire alarm devices. Visual alarm devices
Where products are integrated into a single unit they have to be tested to all applicable EN54 standards.

Others Devices
Audible and visual alarms form the basis of the vast majority of alarm systems; however, there are occasions where they may be supplemented by other devices particularly where the disabled are concerned.
Radio pagers with a vibrate facility, induction loops that communicate with hearing aids and pillow vibrators are all used as additional techniques for fire alarm systems, they are however considered as secondary systems to the main audible and visual alarms, as they do require the user to ensure that they are applied correctly and are serviceable.
There are too many alarm technologies being investigated and developed to be covered in an article like this, but they all have to rely on stimulating at least one of our human senses. In essence, no one type of alarm will provide the total solution to all the needs of any particular installation, but that an amalgam of several techniques will be required to cover all needs.

Bob Choppen is Product Manager at Cooper Fulleon

For further information, go to www.fulleon.co.uk