18 May 2017
Aston Bowles explains why historic structures pose a particularly complex challenge for the people and systems charged with protecting them.
NOT ONLY do historic buildings tend to be complex and varied in their design and construction but their contents will often include furnishings and artefacts of high monetary and cultural value, the loss of which would be permanent and costly to our heritage.
Safeguarding the occupants, fabric and contents of these buildings is of paramount importance, especially where large numbers of staff and visitors are involved, such as in stately homes, museums, or other historic attractions.
An in-depth fire risk assessment needs to be carried out and, in the case of historic structures, normally needs to be supplemented with a more in-depth fire safety management plan, in line with the Regulatory Reform (Fire Safety) Order 2005. The assessment should cover such important factors as active and passive protection measures (both in place and required), mitigation of identified risks, staff training, maintenance and review periods.
At the centre of any active system is the fire panel – single or multi-loop, standalone or networked. The choice available is wide but not simple, and the installation costs are likely to dwarf equipment prices. For this reason, finding a system that is easily installed, with flexible cabling and a range of communication options, should be the priority. Given the complexity of historic sites, an analogue addressable system, which provides more control and scalability, is generally preferable.
A vital consideration with historic sites is the extent to which they allow you to subdivide and control the fire system and its outputs before, during and after a fire condition. The fire system should offer multiple cause-and-effect options to accommodate the wide range of uses, room sizes, layouts, spaces and technical challenges found in such buildings.
Heritage buildings are often in remote locations and difficult to access, and are more likely to be connected to Alarm Receiving Centres. If an unreliable or inappropriate system is installed, the downstream costs of fault-finding, repair and maintenance will be significant.
A recurring challenge is to make the system as unobtrusive as possible without impacting performance. Thanks to repeater panels, the larger fire panel can be hidden from view. Some new repeater panels, such as Advanced’s TouchControl touchscreen, are designed to suit many locations and to flush fit. They include new performance features, such as TouchControl’s digital zone plans and active maps showing fire status throughout a site. An alternative is bespoke cabinets and housings, which can be tailored to fit seamlessly into almost any decorative scheme or hard-to-access space.
The many factors that can create challenges for active fire systems are often aggravated in historic structures: irregular room geometry, large windows, archways, open fireplaces and high, suspended, or decorative ceilings.
The standards for detector placement are dictated by BS 5839, which also gives detailed guidance on the options for different detection types in unusual spaces. Extreme care must be taken to site the detectors such that, in the event of smoke, it can reach the detectors. It is also important to place detectors in such a way that smoke does not stratify beneath the detecting element, or otherwise delay the efficient detection of smoke. Again, BS 5839 provides guidance in this respect.
Different materials will dictate the likely speed and spread of fire in an old building, so detection choice and associated system programming covering the spectrum of operations, from alarm confirmation and alert methods to evacuation strategies and integration with third-party systems, is crucial.
Many detection methods are suitable for historic structures and it’s common to find several of them on a single system. Modern analogue, addressable point detectors are hugely reliable and increasingly sophisticated. The most common type is the optical smoke detector, with many options available in terms of detection and analysis methods. Heat detectors are common in spaces such as kitchens, where steam and cooking smoke are present. Multi-sensor detectors are often used, as they combine heat and smoke detection in a single unit, which can be used as general detection, thus offering real advantages for signal confirmation. Many points can have sounder and strobe options added, or have them ‘on board’ the device. More exotic detection modes, such as CO, are coming to market and are already specified for certain uses in some standards regimes.
Floors and ceilings in older structures are often wooden, so fitting cable systems to approved standards without suspended steel trays can be a challenge. A much less invasive solution uses wireless point detectors, which also come with most of the detection and technology options of their wired counterparts.
Wireless solutions not only mean lower visual and physical impact, they are also faster and cheaper to install. Thanks to two-way communication with the panel, battery replacement and fault reporting can be worked into the ongoing maintenance schedule via the panel service tools, and they are increasingly popular.
Where rapid warning is vital, such as in a gallery space or archive store, aspirating detectors offer a highly effective solution. These continually sample the air, several times a second, and can be set at various sensitivity levels. Although the associated pipework can be bulky and hard to conceal, they are a widely-used option in less prominent, hard-to-access spaces, such as cellars, service areas and attics.
As point detectors are unsuitable for ceiling heights over 10.5 metres, owing to the way smoke dissipates in taller spaces, beam detectors can be used in larger rooms, such as great halls or chapels. They function on the basis of smoke obscuration of a beam of light. The need for a reflector or detector on the other side of the room can make them sensitive to movement, particularly in timber-framed structures, but some of the better beams self-align, minimising the effects of building movement and making installation simpler.
A further option is video and CCD-driven flame detectors, a technology that has developed rapidly in recent years. Although flames will often, although not always, be detected after smoke, these are useful devices where quickly visible flame fires are more likely.
A final detector option, especially suited to sensitive installations, is linear-heat or heat-sensing cable, which can be run through any area. Even tiny changes in temperature cause the conducting cables to short, pinpointing the location and alerting the fire system. In London, the recreated Globe Theatre was able to overcome a 400-year-old ban on thatched roofing using this system. The cables run through the thatch and connect directly to the fire panels, giving real-time indication of any incident.
Another key to effective fire safety is to ensure that a higher level of detection is specified for critical or high-risk areas, such as kitchens, boiler rooms or gallery spaces. Single or multiple detector types can be used, so that incidents are confirmed as quickly as possible and action can be taken without any delay.
Fires can spread very quickly in historic structures, so measures to allow quick extinguishing via sprinklers, water mist or, for high-priority areas, suppressant gas or foam should be considered. The contents of an area may make this difficult, so the speed of detection and alert on the fire system may need to be a primary consideration.
The intelligent zoning of fire systems can be combined with automatic fire doors to isolate the fire and extinguish it, or at least keep it under control until the fire service arrives. This solution was used in the treasury at Lincoln Castle, home of a priceless copy of the Magna Carta, where an Advanced fire panel has been combined with an extinguishing control panel and fire suppression gas to protect the vault. Automatic door controls isolate the space, preventing the fire from spreading and ensuring that the gas is concentrated in the necessary area.
Escape routes that are longer than normally permitted are often a problem in historic properties, especially where they have a residential use, e.g. as hotels or apartments. In such cases, avoiding unnecessary evacuations and helping ensure efficient egress are important functions of the fire system.
In many situations, human intervention is crucial to avoid false-alarm incidents. Remote paging systems, such as the one used in London’s Royal Albert Hall, can alert staff as soon as an incident occurs, and often before, giving them the chance to verify a signal and possibly cancel a false evacuation. The same paging systems can be used to communicate with remote staff and alert those with hearing difficulties to the fire alarm, even when sleeping.
Some fire systems have sophisticated false-alarm management programming built in. This can radically reduce false alerts and evacuations by configuring automatic pre-programmed verification methods and investigation delays, or by allowing trained residents or occupants to verify that signals in their local area (e.g. apartment) are false. Fail-safes are vital and must be part of the default system.
In conclusion, historic structures have always presented a unique challenge for the fire-system industry but innovation is delivering more choice and performance for end-users, specifiers and responsible people in the sector. The choices made need to be based on a thorough understanding of the technology and standards available within the context of a particular site.
Aston Bowles is marketing and communications manager at Advanced. For more information, visit www.advancedco.com