16.07.08
Approval of high-temperature emergency tunnel-ventilation fans: the impact of ISO 21927-3
Although serious fires in tunnels are rare, fires in the Mont Blanc and Tauern tunnels, the Channel Tunnel and the Baku underground system have demonstrated the devastating effects that such underground fires can produce, says Geoff Sheard
In the event of a fire, most tunnel safety management systems rely on an emergency ventilation system to control or extract the smoke and thus maintain a smoke-free route of escape for persons in the tunnel. The tunnel ventilation equipment must therefore be capable of operating at elevated temperatures to remove hot gas and smoke from the tunnel in the event of a fire. Although no global legislative framework exists for emergency tunnel-ventilation systems, the European Community (EC) and the International Organisation for Standardisation (ISO) has addressed various aspects of fire safety in such systems.
The EC introduced EN12101-3 on April 1st 2005, defining the mandatory requirements for CE marking high temperature fans within Europe. The ISO, which is a worldwide federation of national standards bodies, prepares international standards through various ISO technical committees. Each member body which is interested in a subject for which a technical committee has been established has the right to be represented on that committee. Technical Committee ISO/TC 21/SC 11 was formed for the purpose of preparing the International Standard ISO 21927 for smoke-control and heat-control systems. The standard consists of three parts:
* Part 1: Specifications for smoke barriers
* Part 2: Specifications for natural smoke and heat exhaust ventilators
* Part 3: Specification for powered smoke and heat exhaust ventilators
Fans to be installed as part of a powered smoke and heat exhaust ventilation system, including tunnel fans, fall within the scope of Part 3 of ISO 21927-3. The ISO 21927-3 international standard for smoke and heat control systems was developed to provide a globally applicable means of specifying and approving equipment that is used to: (i) facilitate the safe escape and/or rescue of people and animals in the event of a tunnel fire; (ii) protect property; and (iii) enable the fire to be fought while still in its early stages.
The ISO 21927-3 standard requires ongoing conformity to be assessed by the application and maintenance of an audited factory production control (FPC) system. An FPC system that complies with ISO 9001:2000 is advised, but this must be made specific to the requirements of ISO 21927-3.
The classifications derived for powered smoke-exhaust and heat-exhaust ventilators (fans), which have been incorporated in ISO 21927-3, are as follows:
* F200: a constant temperature of 200°C for 120 minutes;
* F300: a constant temperature of 300°C for 60 minutes;
* F400: a constant temperature of 400°C for 90 or 120 minutes;
* F600: a constant temperature of 600°C for 60 minutes; and
* F842: a constant temperature of 842°C for 30 minutes
The test method for fans is given in ISO 21927-3. The fan is tested as a complete assembly - that is, with dampers or deflectors, if fitted. The fan is tested in - or connected to - a furnace at the specified temperature. The performance is determined by testing the fan such that, at normal ambient temperature and pressure, the power output is 80% to 100% of the maximum absorbed power of the fan and it is operating anywhere on its volume pressure curve, provided that the volume or pressure reading are stable. The fan is shown to be functioning satisfactorily if it can continue to provide the initial volume or pressure, within the defined limits of the test method.
The design of tunnel ventilation systems is typically application-specific and it is therefore often necessary for large tunnel fans within such systems to be tailored to the specific requirements of each project. The design and complexity of such fans can differ significantly from one tunnel to the next, especially in the case of longer tunnels. Despite the difficulties that arise as a consequence of tunnel to tunnel variation in ventilation equipment, compliance with ISO 21927-3 is likely to become mandatory as tunnel designers continue in their drive to improve tunnel safety.
Fläkt Woods has undertaken a major testing programme to certify its range of axial flow fans from 315 mm up to 2.8 meters, for use at 200C, 300C and 400C. Together with a comprehensive range of auxiliaries, Fläkt Woods is therefore able to provide an extensive range of fans for tunnel and metro application that comply with both the European requirements of EN12101-3 and ISO 21927-3 globally.
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