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Taking the heat

The complexities of modern transport hubs mean there is no such thing as a standard fire system. Aston Bowles of Advanced looks at the issues involved in protecting the travelling public

From local bus stations to major airports, the term ‘transport hub’ embraces all manner of buildings and facilities, both above and below ground. They all need to accommodate large groups of people, moving rapidly from one location to another, all of whom need to be safeguarded. As a critical part of our urban infrastructure they are invaluable and expensive assets, where disruption can often cause knock-on effects across cities and borders. They are environments where precision, reliability and speed are required from the fire system.

Advanced panels are installed in transport hubs all over the world, from the Tyne Tunnel, London’s Underground and Crossrail to Abu Dhabi Airport networks and the historic Peak Tram in Hong Kong. The combined expertise of the sector’s leading specifiers, installers and manufacturers means the latest fire systems offer customisable solutions for transport hubs, from multiple detection methods and voice evacuation to complicated cause and effect, false alarm management and remote monitoring.

With so many people flowing through transport hubs, often in restricted space, any evacuation is a serious issue. This means it’s vital that evacuations are only initiated in genuine emergency situations, and not from false alarms.

False alarm management techniques have evolved rapidly in recent years, with best practice focusing on the fire panel, intelligent detection systems and trained users. The nature of transport hubs means there can be very few or no delays between a detector signal or activation and an alarm condition. Staff must be trained to respond quickly to signals, and those responsible for the system must have as much information available as possible to make decisions and act.

Building management systems (BMS) and graphics systems bring detailed system data back to a central point, allowing fast, measured decision-making. Secure fire paging systems can ensure staff on site receive vital information such as pre-alarms directly from the fire panels. Networked panels and repeaters can offer network-wide information and control to ensure response times are short.

Transport fire networks are often very large, with many panels, detectors and input and output devices. To achieve the required levels of reliability and response, the networking and loop protocols must be efficient and fast with real data integrity.

Ensuring cable paths are insensitive to electromagnetic interference is important, especially in restricted spaces, such as tunnels, where all manner of data and power are in close proximity. Some fire systems are designed with in-built diagnostics and processing tools to ensure installation accuracy and data integrity.

In the case of genuine alarms, the dynamic fire situation must be presented clearly. Graphical repeaters use touchscreen technology to deliver ‘zoomable’ dynamic maps of sites and pinpoint the exact location of the fire.

As fire panels have become more sophisticated, so have the latest detectors. Some offer unprecedented levels of intelligence and signal processing, offering specific settings, sensitivities and operating modes for installation areas and conditions. They offer more integral sensors and on-board processing, can discriminate between valid and false signal sources, and can be combined with or have integrated signalling devices at the same point.

Transport hubs present a series of detection challenges, ranging from the complexity of the layout – anything from narrow tunnels to vast open spaces – to difficult environmental conditions and the potential for erroneous signals (such as diesel fumes in a bus depot or covered station). Addressable point detection ranges, that include smoke, heat and multisensor options, will be the mainstay on many sites or, where wiring is an issue, wireless devices can be used.

Due to the way smoke disperses in loftier spaces, such as airport departure halls or Victorian stations, point detectors can be unsuitable. Beam detectors are an ideal alternative, being simple to install and offering active protection by measuring the obscuration of a beam of light by smoke particles.

In hard-to-reach spaces, such as an underground substation, plant room or airport fuel store, aspirating detectors offer an effective solution. Linear-heat or heat-sensing cable detectors can be run through any area to provide early and accurate warning of fire. In some areas, multi-channel flame detectors, which can offer remote visual confirmation, are the only option.

In transport hubs, evacuation can involve thousands of people, so pre-planning and coordination are vital. A disorderly evacuation can result in severe delays, with queues, clogged evacuation points and even crush situations all having the potential to cause death or injury.

The fire system will be called upon to process millions of inputs and outputs as a fire spreads, including false alarm management, smoke control, graphical indication, door closures, direct connections to monitoring stations, gas suppression, and voice evacuation. The processing power of the panel is vital and in larger hubs, such as an airport or city centre station, a fast fire system can maximise the window for verification, evacuation and firefighting.

A fire panel should also be able to manage phased evacuation, using cause and effect and recorded messages or live voice (standards dependent) to facilitate the escape of those most in danger, while maintaining a manageable flow of people from the rest of the complex.

Emergency lighting systems are crucial, and have developed rapidly in recent years to offer internet monitoring and automated testing. Advanced’s Lux Intelligent, for example, will work with almost any light, ensuring compliance across a whole site or multiple sites anywhere in the world.

In a large transport hub, with combinations of open and enclosed spaces, voice alerts, tones, bells and strobes can all occur at the same time. The clarity of these warnings is very important as any misunderstandings could be deadly. Ensuring that voice messages, live announcements, sounders and strobes remain understandable and synchronised can be a major challenge. Software such as Advanced’s PerfectSync manages audio and strobe synchronisation across a site, ensuring occupants always receive clear alerts or messages, even in the most dynamic circumstances and when the fire service is making live voice announcements, which is common in some jurisdictions.

When required, transport hubs will use an addressable fire system for general detection and alarm, with a dedicated or integrated extinguishant release system alongside.

Suppression systems come in a wide range of configuration options, from networked and interlinked systems to completely standalone. The choice of solution will depend on the budget and performance required. Extinguishing systems are often designed around flooding and detection zones. Detection zones are used to ensure signals are valid and double-knock signal confirmation is very common, using two detection circuits or zones to confirm a signal before activating a release.

A flooding zone is the area in which suppressant will be released and, given that chemical suppressants can be harmful, it is often preferable to use water sprinklers in public areas, with gas-based suppressants in more sensitive spaces.

Most extinguishant release panels will be in manual operating mode when people are on site, but can be switched to auto to cover all eventualities. Most systems will also have hold and abort buttons that allow the extinguishant release to be paused or cancelled on visual confirmation of the alert.

Another challenge facing transport hubs, particularly those across multiple levels and underground, is smoke control and air flow, both in aiding firefighters and ensuring that evacuation routes are kept clear. This can be managed via fans and dampers, using either the building’s HVAC (heating, ventilation and air conditioning) or a dedicated system to manage airflow through the building.

The HVAC system is crucial in a fire situation. It covers every area of the transport hub and can have a major influence on the extent and spread of the fire as well as the smoke, which often poses more of a threat to life.

Modern smoke control is an active and dynamic tool in firefighting and the evacuation of transport hubs. The best fire systems can manage smoke and airflow through a building automatically and manually, to keep positive pressure in evacuation routes, clear smoke from a particular area, or to pressurise a space.

In some situations, for example in a major airport or terminal station, even the reliability of today’s best systems is not enough and system redundancy should be considered. Specifically, this means that parts or all of a system will be seamlessly replaced if they fail. For example, if a panel or processor stops working there is a twin, identically programmed, device ready to take over.

In summary, there is no ‘standard’ fire system solution for any transport hub. As our transport systems become integrated and more complex in terms of size, structure and user need, fire systems themselves become more complex. Specifiers and users need to understand the features and benefits of the solutions available, as well as how the fire systems themselves can help deal with complexity.

About Sarah OBeirne


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