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ÐÇ¿Õ´«Ã½ services consultant WSP Group has carried out extensive research into wire-free systems in recent years. The company has experienced reliable and trouble-free operation of radio fire alarm systems in many different applications over a number of years.

A wire-free fire detection system uses secure, licence-free, radio communications to interconnect the sensors (smoke detectors, manual break-glass callpoints etc) with the fire alarm control panel. The sensors are typically self-powered with built-in energy packs. A simple concept, but one that brings many advantages through the elimination of expensive fire-rated cable.

The use of wireless signalling has been around for over 30 years, with the majority of the early products coming from the USA or Far East. The integrity of radio fire systems has improved considerably over the years, in part due to the involvement of UK manufacturers. UK suppliers include EMS and Electrodetectors.

In 1988, the revised BS 5839: Fire detection and alarm systems for buildings was published, and included the acceptance of radio as a means of signalling fire alarm systems.

The Radio Communications Agency tightly controls the radio frequencies available for use in the UK and only agrees their operation after they have been tested and proved to meet the relevant standards. This means that any radio equipment used must carry approval, and there should be no interference between any systems.

Part of the remit of the Radio Licensing Authorities is to ensure that each of the major services has its own separate allocation from within the frequency spectrum. For instance, each of the following applications are segregated to prevent interference: TV broadcasting; emergency services; mobile telephones; private mobile radio; airport ground support; radio microphones and car alarms (key fobs).

This segregation, together with the secure dual-frequency signalling that modern radio alarm systems utilise, ensures that false alarms due to radio interference cannot occur.

Modern radio fire systems are analogue addressable and provide all the features you would expect from any fire detection system, including networking (radio based), repeater panels, paging and cause and effect programming. The devices used are often based on industry standard sensors, sounders and callpoints and are aesthetically pleasing, with built-in aerials that are hidden from view. Many radio systems also incorporate products such as multi-sensor fire detectors and combined sounders and fire detectors in one unit.

There are few instances where radio fire alarm systems cannot be used and they can be installed in almost any commercial and industrial application. There are however, a number of applications where radio systems can provide significant advantages:

• hotels and homes – a hotel or residential home can be refurbished with a new radio fire detection system without affecting room occupancy and services. A bedroom can be fitted with a fire detector and sounder in less than ten minutes;
  
• temporary protection – building sites and entertainment events that require temporary protection are ideal for the flexibility of radio systems. The detection devices can be easily changed with the environment and the systems can be rented for short-term applications or purchased and moved to the next site upon completion. Radio can also be an ideal solution for many commercial installations where full protection is required in the interim, but the final installation would form part of the tenant's fit-out package;
  
• heritage – historic buildings or those with expensive finishes requiring refurbishment can have a radio system installed without disturbing the decor;
  
• asbestos – buildings with asbestos materials that would be uneconomical to remove can be easily protected without disturbance. Devices can be fitted to ceilings without the need for drilling;
  
• open plan – buildings without suspended ceilings can benefit from the reduction of visible services and wireways. The protection of open plan offices can be easily moved as the environment changes without the need to move or rerun cabling;
  
• site wide – developments with multiple buildings requiring central control can be fitted with a radio system, thereby removing the need to interlink buildings with cabling. This eliminates expensive external infrastructure works;
  
• large developments – medium and large developments can benefit from the reduced labour time associated with radio alarm systems. A typical radio smoke detector takes just ten minutes to install;
  
• expansion – radio systems can be easily interfaced to existing or obsolete wired systems that need expansion or upgrading.

Advantages
Independent research conducted by cost consultant Davis Langdon & Everest concluded that on many typically-sized commercial installations, radio alarm systems were cost-competitive with hard-wired systems. On large installations they were cheaper due to the significantly reduced labour costs. On refurbishment projects, particularly in historic and listed buildings, the advantages are significant.

The flexibility in positioning of devices allows the design and installation to be detailed late in the programme, thus eliminating the cost and time involved with late client changes. Additional devices such as smoke sensors and callpoints can be incorporated, removed or repositioned with minimal disruption. The system can also be easily modified and expanded in the future, even when the building is occupied.

As a typical radio device such as a smoke detector can be installed in less than ten minutes, this reduces the disruption of services and normal activities during refurbishment to occupied buildings. This also has a cost advantage in applications such as hotels, dealing rooms and residential homes, where building occupancy would be largely unaffected.

As no cables or wireways are needed, damage to the fabric of the building is significantly reduced, which is an important consideration in historic buildings.

Multiple buildings can be linked without the use of interconnecting cable, thus avoiding expensive external infrastructure works. The cost to dig up ground, install underground ducts and refill could have a major impact on a project. Even overhead cables could have a similar impact.

Wired fire alarm systems rely on expensive fire-rated cable to ensure continued safe operation during a fire. Radio systems eliminate this need as the signalling is unaffected by fire.

Assuming a thorough radio survey has been undertaken and the system has been installed correctly the risk of damage or corruption to the signalling path is eliminated. There are no cables to break or short out. Radio systems are tolerant to hostile environments, as is borne out by the type of installations that currently exist, including MOD bases, airports and air traffic control centres.

Disadvantages
The costs of devices and control panels are higher compared to typical wired-systems due to the additional radio electronics and local power requirements. However, the equipment cost cannot be taken in isolation and total project costs need to consider the reduced expense of installation. The lower labour costs typically offset the higher equipment costs. Typical cost breakdowns are:

• wired systems – 50% labour costs, 50% material costs;
  
• radio systems – 15% labour costs, 85% material costs.

Each radio device has to be locally powered from a power supply or by batteries. Modern radio devices have built-in battery power packs, which typically give a five-year life under normal operating conditions; normal operating conditions include regular system tests, with sounders, as specified in the standards. Typical battery packs have utilised lithium batteries but the latest devices now use alkaline batteries, which reduces the cost of replacement and reduces the impact on the environment.

The health of each battery pack is monitored by the system and a low battery warning is raised well in advance, often allowing replacement to be undertaken during normal maintenance.

Clearly there is an additional ongoing maintenance cost with radio systems but with the lower costs of alkaline batteries, and as the removal of the need to perform cable integrity checks, there is little difference between radio and wired systems. The batteries can be replaced with those sold on the high street.

Before any design or installation is undertaken it is essential that a trained qualified engineer should carry out a radio survey. The survey will determine the most appropriate radio receiver, transmitters, type and location of aerials and positioning of devices. This is an essential exercise, and it is important that this process is performed with the utmost care to provide trouble-free operation.

The way forward
Radio systems are now also becoming significant in high security applications and voice evacuation. The integrity, reliability and flexibility of radio fire systems have been incorporated in products that can solve a diverse range of security applications. All the advantages of a wire-free environment are just as relevant for security as they are for fire.

  Radio systems can also provide building-wide voice evacuation including public address facilities, without the need for cable. These systems can easily be interfaced with radio fire and security systems to provide site-wide fully integrated wire-free protection systems.