Published: 01 January, 2006
The recent DDA and EN54 directive has once again placed emphasis on the importance of ensuring safety and warning systems are up to standard. Not only that, but there is also now a need for companies to install more versatile systems that can cater for both the visually and audibly impaired.
However, the sheer choice of alarm warning systems available today makes this no easy task. From 32 tone interior sounders to wide area disaster signals, revolutionary directional sounders to state of the art desktop evacuation software; how can companies choose what is best for them?
What is available today?
Most alarms in the UK rely on rudimentary warning systems, many of which involve little more than a simple bell or electronic sounder. The vast majority, however, have now been developed into more sophisticated units which offer superior audibility and a wider range of tones.
Due to customer demand, modern sounders have been designed to overcome the problems associated with early electronic sounders, such as high current consumption. Typically, they now draw less than a tenth of the power of their predecessors and many sounders are available with very low consumption, in the 3mA to 5mA range for outputs of around 100dB (A).
Many products are now available with a relatively high sound output and wide choice of voltages, often incorporating up to 32 tones. Where a unit is required to perform in both indoor and outdoor applications, appropriate weatherproofing is fitted. It is also possible for this type of multi-purpose product to be fitted with a beacon should the need arise.
The introduction of multi-tone sounders and voice sounders has come some way towards addressing the need for alarms that are situation specific, whereby a tailored message can be emitted in place of a standard alarm tone.
Additionally, many countries now have their own specific, well recognised alarm sounds and emergency evacuation signals as well, and though this is not the case in the UK it does mean that products aimed at international markets need to cater for these localised needs.
Providing clear warnings
Where voice-enhanced sounders are specified, they can provide the user with a clear and precise safety warning. User recordable sounders allow customisation of messages as well as allowing users to record multiple messages. These sounders are designed for use within the fire and industrial sector to enhance safety and security.
Other sounders currently available include those designed principally as ceiling mounted units for use in fire alarm systems in areas with low ambient background noise. Intended to be fitted under proprietary smoke and heat detectors, a sounder and detector can be located at the same point, saving both time and materials. Low current fire alarm sounders are ideally suited for long cable runs where a low current draw is required.
For outdoor applications, particularly where there is high ambient background noise, powerful disaster warning sounders are available. They generally have an output of around 140dB @ 1m, making them ideal for the large industrial sites where they are often situated. Rugged by design, these outdoor wide-area use sounders offer higher audibility to enable the sound to carry over large distances. Some can also offer the facility of voice/PA capability.
Lighting the way
As the fire safety market has evolved, so has legislation. The Disability Discrimination Act in particular has forced companies to consider the need not only for audible alarms, but also visual. This has led to the introduction of combined multi-tone audible/visual units.
Sounder-beacon combination units are a necessity in many applications, not just when it comes to catering for the audibly or visually impaired. In a smoke-filled area a guiding emergency light on its own is insufficient, and in high noise environments a sounder may not be heard. This means that the ideal solution is a system that incorporates both.
High current consumption has long been an issue associated with beacon use, with xenon beacons often drawing excessive currents and most taking large current surges after each flash. This effect is often compounded when many units are used together, and the cumulative effect can cause overloads in power supplies that may in turn disrupt other parts of the system.
In addition to ensuring low current consumption, reliability and synchronised beacon flashes are of paramount importance in security and fire installations. With all this in mind, there are now beacons available which use light emitting diodes as an alternative.
LED beacons can produce light outputs similar to that of their xenon counterparts for currents of around 3mA. This allows the user to integrate these units with sounders, lowering installation costs and finally making loop-powered sounder beacons a real option.
Regardless of the type of sounder used, it is essential that the unit be installed correctly to ensure maximum sound and light exposure. As sounders are designed to project a multi-directional sound, the centre of a room or wall is the most appropriate position for installation, though this may vary in areas with high noise hotspots.
To check that the sounder can overcome any existing noise, background audibility should always be assessed prior to commencing installation. Sounders that incorporate beacons must be visible to the eye; in contrast there are no real height issues with audible sounders. Naturally, if the unit is to be installed outside if must be weatherproof.
A growing demand for products that make use of sound for evacuation as well as alarm purposes has given rise to the development of directional sounder technology. New types of fire alarm sounder use this to guide occupants of a building to the emergency exits, making escape easier and quicker for all occupants, particularly those with impaired vision. As fatalities in fires are often caused by inhalation of poisonous gases in smoke, these sounders help to save lives by minimising evacuation time.
Conventional fire alarm sounders use narrow sound frequencies which the brain cannot localise. This means that they merely alert listeners to the presence of danger rather than providing them with information on the nearest emergency exit - something they must ascertain from the fire exit signs alone.
In order for exit sounders to be located by the brain, the frequency content of the sound has to be as wide as possible (20 - 20,000 Hz). Sounders using directional sounder technology emit a broadband, multi-frequency sound, commonly referred to as white noise. The direction of this can be easily detected by the brain, and a rising or falling tone is intuitively understood to mean that the listener must either ascend or descend the stairs.
Used in conjunction with modern analogue addressable fire detection systems which can determine the source of a fire, a preferred evacuation route can be set by triggering the appropriate directional sounders.
A further step beyond the realms of traditional security systems comes in the form of emergency warning computer software. Such software can enable orderly evacuations by transmitting tailored instructions and exit maps in front of each PC user exactly when they are needed, overriding whatever is displayed on screen. The systems are designed to complement audible warning systems and can be configured to warn of fire, security and other hazards. They can also be used to call individuals to help, such as fire or evacuation wardens.
If fire breaks out and a building needs to be evacuated, such systems can also display maps, assembly points, sounds and animations to aid a swift and orderly exit. Programs can also be customised to display other messages, for example to alert First Aid personnel to an incident within the building, or to discreetly summon security staff.
Legislation plays a key part in keeping sounders and safety systems up to date. For example, the Construction Products Directive (CPD) requires that all fire system sounders, point head detectors and point smoke detectors sold in Europe after June 2005 must comply with the relevant part of EN54 (ie parts 3,5 or 7).
Other fire detection system products sold in Europe also need to comply with the relevant part on EN54 (rather than the national standards) at a future date. The impact on businesses in terms of time and costs required for product testing, approvals and amendments is as yet unknown, but the impact is expected to be significant.
Organisations should now have taken steps to ensure they are acknowledging, and indeed embracing, the advice in the CPD. Where fire and security systems are concerned, the directive implies that fire equipment should be approved and tested by a certified body to show compliance to the CPD. Furthermore, it urges businesses to ensure that all product developments fall in line with the stated guidelines.
As mentioned earlier in this article, the Disability Discrimination Act (DDA), which came into force in the UK in October 2004, will have a massive impact on all businesses regardless of trade or industry.