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Malls require unique fire detection designs

New shopping malls have been springing up all over Africa, and their innovative architecture presents both a major challenge and a wonderful opportunity to fire safety professionals. Fire safety for these malls, and others yet to be built, is a complex challenge.

Invariably, given the inherent uniqueness of every mall, designing fire detection systems for each one will involve performance-based design that goes beyond codes and standards in order to provide suitable protection for a very complicated and unique building.

Fire detection for unique structures

Spectacular destinations such as the Kenya’s Two Rivers Mall and the Gateway Theatre of Shopping in South Africa invariably play with the power of space, and this is at the core of the fire detection problem that must be surmounted. Their soaring atria and cavernous halls provide a suitable sense of grandeur, while also being highly flexible in combining shopping with food and entertainment. Beyond the Instagram-friendly architecture, a network of car parks, cable ducts, utility tunnels, power and data hubs, hide further fire hazards in often hard to access areas.

These complexes regularly host thousands of visitors and staff at peak times, who would all need to be safely evacuated should a fire take hold. Alarming early is therefore essential in order to react with measured increments and prevent a panic, and while fire detection can be difficult in such complex environments, it is equally important to avoid false alarms. Only the combined use of advanced detection methods, with suitable networking and well-trained staff, will satisfy all of these requirements.

Challenges of open spaces

One of the primary fire safety concerns for large open spaces and open plan areas within buildings is the potential for rapid spread of fire and smoke. In cases of open spaces between floors or with large vertical openings, a fire on a single floor can cause fire and smoke to spread upwards throughout the building very quickly. This is particularly true of flexible spaces such as malls, where typically, a series of individual shops are located on different levels, connected by the open space of the main covered public area.

Another fire safety challenge is the need for safe evacuation of large numbers of people through designated egress routes. Early alarm is therefore paramount to both life and building safety when it comes to large open spaces. Early fire detection is also needed to trigger other consequential events or actions; these range from power-down processes to the control of emergency lighting and smoke management systems, and the actuation of sprinklers or other suppression.

Stratification and air conditioning

A key problem with fire detection in large spaces is their potential for smoke stratification and dilution. In spaces with high ceilings, the smoke plume from an incipient fire will mix with vast amounts of additional cooler air as it rises, and this will alter its buoyancy and temperature. This phenomenon means that the time required for smoke to reach sufficient density to trigger an alarm can be affected significantly. Indeed, stratification effects can mean that smoke will not reach detectors placed under the ceiling at all.

Additionally, shopping malls in Africa are invariably air-conditioned. In ambient-controlled environments, higher airflow will also dilute and dissipate smoke quickly. The time required for a smoke detector to activate will depend on how sensitive it is and where the sampling points are located, which requires careful planning and potentially testing in real-world scenarios, given that large malls are invariably unique in both layout and airflow.

Performance-based design is essential

Fire and building codes continue to evolve, but cannot hope to keep up with the pace of architectural ambition when it comes to an innovative industry like retail. This forces fire safety professionals into a fundamental shift from the traditional prescriptive Deem-to-Satisfy design based on regulations, to a risk-informed approach and performance-based design (PBD).

In these complex and unique environments, quantitative risk assessment requires the same smoke detection system to, not only provide early warning in various fire scenarios, but also to work reliably in different building geometries or changing ambient conditions inside the protected areas. This is particularly true given that many modern malls are designed as multi-use and require the ability to alter aspects of the internal layout on an occasional basis, in order to accommodate changing needs from leaseholders.

Designs that offer suitable protection for major shopping malls will likely rely on a variety of advanced fire detection methods. While networked point-type detectors may have their place in the individual shops and cafes, the aforementioned stratification and dilution issues mean the large open areas will require powerful detection at multiple points and at different heights. Aspirating smoke detection is ideal for this use, as the tubing can run vertically with a suitable number of sampling holes along its length.

Advantages of aspirating smoke detection

Aspirating smoke detection (ASD) also offers low visual intrusion, wide coverage, and an ability to reach into areas of difficult access without the need for regular maintenance access. An ASD tubing layout can be designed to cover an atrium or shopping hall across both a horizontal and vertical cross section, while also providing additional detection around smaller units, in a way that is straightforward to alter, should the space requirements and uses change. Crucially, pre-placed test holes located for easy access allow for testing the entire system effectively.

ASD also offers over beam detectors, which are often used to protect atria or domes, but cannot function if internal structures block the line of sight – or may block it on occasions or in the future. Allowing for flexibility of use is likely to be a key demand as mall and entertainment venue operators consider the need to continue offering new elements to keep their appeal fresh in the face of ever increasing competition.

Linear heat for cables and car parks

ASD tubing is also an option for protecting cable trenches and trays, and other utility tunnels which will invariably run for kilometres around a large site. However, the longer these become the more cost-effective a linear heat system is likely to be by comparison, especially one where a sensor cable can simply be laid alongside in the cable tray. Linear heat detectors are also popular options for the car parking areas attached to almost every major destination building.

Complex structures lend themselves to an imaginative mix of fire detection methods, suitably designed, tested and networked. For fire safety professionals across Africa, the business potential from new malls and modernisation work at existing shopping centres is considerable. To take advantage of this booming sector, all they need is familiarity with the best fire detection methods and a grasp of performance-based design.

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