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From page 23... ... 23 Tunnel Emergency Ventilation and Smoke Control Design Guidelines The purpose of controlling the spread of smoke and maintaining a tenable environment is to keep people in a smoke free or survivable environment as long as possible or for at least the duration of evacuation and rescue. This can mean one or both of the following: • Keep the smoke stratification intact, leaving more or less clean and breathable air suitable for evacuation underneath the smoke layer to both sides of the fire (applicable to bi-directional or congested uni-directional tunnels and is typically achieved by zoned transverse ventilation or single point extraction as discussed in the following sections) Read the entire page →
From page 24... ... 24 the length of the tunnel roadway. There are also many combinations of different types of basic ventilation such as single point extraction, ventilation with intermediate shafts, etc. Read the entire page →
From page 25... ... 25 the chimney (tunnel) Read the entire page →
From page 26... ... 26 The traffic condition may need to be evaluated. For example, in uni-directional tunnels, the assumption is made that in a fire emergency, the tunnel will be closed for on-coming traffic; some traffic will be trapped behind the fire while traffic downstream of the fire will leave the tunnel. Read the entire page →
From page 27... ... 27 The vehicle drag coefficients are measured using wind tunnel tests. Heavy duty vehicles such as trucks and buses have larger drag coefficients than passenger vehicles typically in the range of 0.6 to around 1.0. Read the entire page →
From page 28... ... 28 assumption that drivers downstream of the fire are free to escape by continuing to drive towards the exit portal while drivers upstream remain behind the fire. Other types of traffic flow, including bi-directional traffic and uni-directional congested traffic, are better supported by other ventilation schemes. Read the entire page →
From page 29... ... 29 the decrease of air density during a fire event results in the lowering of the driving force of the jet fans that work in the hot air. Jet fan sizing is usually limited by the space available for installation in the tunnel (see Section 3.3) Read the entire page →
From page 30... ... 30 air flow development in the tunnel. Silencers and vanes cause additional resistance to the airflow which results in a reduction of fan thrust. Read the entire page →
From page 31... ... 31 fore, are suitable for relatively short tunnels unless supported by other ventilation schemes. The Saccardo nozzle ventilation scheme may not be as effective for fires near the injection point, possibly up to a few hundred feet downstream, as air recirculation may occur near the fire. Read the entire page →
From page 32... ... 32 3.1.4 Transverse Ventilation Transverse Ventilation is a system that is applied for smoke control when the smoke stratification must be kept intact, leaving more or less clean and breathable air underneath the smoke layer to both sides of the fire while extracting smoke from the fire site (applicable to bi-directional or congested uni- directional tunnels) Read the entire page →
From page 33... ... 33 the fire site is very large and impractical to achieve for long tunnels. There are many combinations of different types of basic transverse and semi-transverse ventilation such as single point extraction, ventilation with intermediate shafts, etc., which implement elements of longitudinal and transverse ventilation schemes. Read the entire page →
From page 34... ... 34 Also, it is important that no jet fan is turned on in or near a place where there is smoke, as this would immediately destroy the smoke stratification. 3.1.7 Semi-transverse Supply System A semi-transverse supply system is not effective for smoke management as it is unable to maintain smoke stratification or provide smoke extraction at the fire site. Read the entire page →
From page 35... ... 35 Tunnel height and width and grades are factors to be considered. Tunnel geometry affects the following two areas: • "critical velocity," which has a direct impact on ventilation requirements, and • ventilation system design. Read the entire page →
From page 36... ... 36 The maximum air velocity limitation for fire emergencies is set based on the ability of people to walk in a high air speed environment [1] Read the entire page →
From page 37... ... 37 These relative merits are crucial at the initial concept phase, when deciding on the type of ventilation system for any particular tunnel. 3.2.2 Traffic Conditions Short rural tunnels with uni-directional light traffic with no flammable cargo and no HAZMAT could be justified for natural ventilation. Read the entire page →
From page 38... ... 38 following minimum measures shall be taken with regards to ventilation: • Air and smoke extraction dampers shall be installed which can be operated separately or in groups. • The longitudinal air velocity shall be monitored constantly, and the steering process of the ventilation system (dampers, fans, etc.) Read the entire page →
From page 39... ... 39 flow measurements have to be carried out in order to ensure that the flow measurements are reliable and representative for the actual flow situation in the tunnel. Interference of the airflow control devices with the smoke extraction should be avoided, e.g., by not using jet fans that are situated close to the smoke extraction zone. Read the entire page →
From page 40... ... 40 Figure 3.13. Typical jet fan installations in road tunnels. Read the entire page →
From page 41... ... 41 It is advisable to select the largest fan that can be fitted within the allocated space. Larger fans give a higher ratio of thrust to both capital and installation costs than smaller fans. Read the entire page →
From page 42... ... 42 French guidance provides smoke temperatures at various distances (CETU, 2003) Read the entire page →
From page 43... ... 43 Several fans installed in parallel typically serve a single ventilation duct due to high airflow requirements and relatively low pressure needed. Fans operating in parallel should be of equal size and have identical performance curves. Read the entire page →
From page 44... ... 44 motor durability, generator sizing, flexibility of the system, efficiency, etc. 3.4 Effects of Ventilation on Tunnel Fires and Fire Sizes Ventilation has an influence on fire development, but it does not always conform to expectations; this influence depends on the location of the fire origin and the sufficiency of air [44] Read the entire page →
From page 45... ... 45 and more difficult to maintain as the distance from the fire increases. Thermal pressure tends to maintain smoke stratification but the inertia force tends to destroy it. Read the entire page →
From page 46... ... 46 The exhaust ventilation system should be sized to extract the smoke flow rate, which depends on the FHRR, gas temperature, tunnel geometry, and ventilation. When the smoke layer is relatively shallow, a high extract rate at any point may lead to "plug-holing", where some air is extracted from below the smoke layer as opposed to the smoke itself. Read the entire page →
From page 47... ... 47 defined to apply outside a boundary away from the perimeter of the fire, it is practical to consider a smoke extraction zone of not less than 90 m (300 ft) long with at least 3 exhaust openings spaced at least 30 m (100 ft) Read the entire page →

From page 23...

... 23 Tunnel Emergency Ventilation and Smoke Control Design Guidelines The purpose of controlling the spread of smoke and maintaining a tenable environment is to keep people in a smoke free or survivable environment as long as possible or for at least the duration of evacuation and rescue. This can mean one or both of the following: • Keep the smoke stratification intact, leaving more or less clean and breathable air suitable for evacuation underneath the smoke layer to both sides of the fire (applicable to bi-directional or congested uni-directional tunnels and is typically achieved by zoned transverse ventilation or single point extraction as discussed in the following sections)