Petr Pospisil - Academia.edu (original) (raw)

Papers by Petr Pospisil

Underground. The Way to the Future, 2013

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Fractures in the blading of jet fans pose a serious risk to the traffic inside the tunnel. This c... more Fractures in the blading of jet fans pose a serious risk to the traffic inside the tunnel. This concerns on the one hand the non-availibility of the fans as an important part of safety systems, and on the other hand the endangerment of vehicle occupants by fractions flying around. The precautionary measures used so far for supervision consist only of a regular measurement of the RMS values of vibrations at the fan housing, which provide insufficient information about previous damage to the blades. In this paper, an experimental method is presented with which cracks and already existing partial fractures in the fan blades as well as other anomalies in fan operation can be reliably detected. Although the procedure is more complex than the usual simple vibration measurements, it can be carried out within the scope of the regular maintenance and inspection of the tunnel ventilation equipment.

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Geomechanics and Tunnelling, 2022

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The philosophy of fire ventilation in road tunnels has been improved in the past years. The goal ... more The philosophy of fire ventilation in road tunnels has been improved in the past years. The goal of fire ventilation for smoke control is the handling of the longitudinal airflow. This is important for tunnels with smoke extraction as well as for short tunnels with only longitudinal ventilation. In order to control the longitudinal airflow, jet fans are required. In special cases, for example in case of a powerful transversal ventilation with several ventilation sections, the airflow can be controlled without jet fans. The best method to control the longitudinal airflow is by means of a closed-loop control. The control routines must be based on a physical model of the tunnel. Furthermore, the measurement of airflow in the traffic space becomes essential. Nevertheless, the application of the new fire-ventilation philosophy in practice is not simple.

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For road tunnels with and without smoke extraction, the control of longitudinal airflow is essent... more For road tunnels with and without smoke extraction, the control of longitudinal airflow is essential in order to limit smoke propagation in case of fire. Various concepts for the handling of longitudinal airflow have been investigated. These include jet fans, the use of (semi-)transverse ventilation, directed point air injection (Saccardo-nozzles), local air extraction, air curtains and mechanical curtains. At present, the application of jet fans is the standard solution, but not necessarily the optimum for all applications. Jet fan installation in the traffic envelope often leads to problems with corrosion and accessibility for maintenance and repair. Jet fans require extra space under the ceiling or in niches. This may lead to high additional costs if jet fans have to be retrofitted during ventilation system upgrades in existing tunnels. Particular attention is paid to the rededication of existing supply air ducts in tunnels with transverse ventilation systems. Many tunnels of medium lengths were equipped with this kind of system when vehicle emissions were very high and the need to control the longitudinal airflow was secondary. In many of these tunnels, the distributed air extraction is going to be abolished during a safety upgrade and replaced by concentrated smoke extraction through remote controlled dampers. Distributed supply air is no longer needed because for mechanical ventilation in normal operation, concentrated extraction or longitudinal ventilation can be applied. As these supply air ducts are connected to functioning ventilation stations a new use for them suggests itself which could be an economic application of control of the longitudinal air flow in case of tunnel fires. This leads to the concept of directed point air injection, which is one of the main focuses in this investigation. Many descriptions of simulations, small-scale tests and real tunnel applications are found in the available literature. The one-dimensional calculation method by application of the energy equation and the balance of momentum is well established and very similar to that used for the design of jet fan applications. Nevertheless, some decisive parameters are uncertain and depend on the actual layout. To reduce the uncertainties, a series of tests has been performed with a full scale model of a Saccardo nozzle in an existing road tunnel. The results of the measurements and simulations are in close agreement to the assumptions applied. They enhance the knowledge about the decisive parameters. Limits for the application of point air injection have been identified.

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Ventilation is one of the most important systems that enhances the safety of a tunnel. Most venti... more Ventilation is one of the most important systems that enhances the safety of a tunnel. Most ventilation systems are designed in first order for the emergency case, i.e. the fire ventilation, and many are hardly ever used in normal operation. Only by rigorous testing, the practical functionality of equipment and the whole system can be proven. Besides the usual factory and site acceptance tests of equipment, the focus is on the proper control algorithms and integral functionality of the whole system. The control of the longitudinal airflow is essential to confine the spread of smoke. Realistic smoke tests prove the proper function of the automatic smoke detection and show the performance of the fire ventilation. Practical experience from those tests leads to findings that should be considered in the concept and design process. This is particularly important where requirements in actual design guidelines were based mostly on mere theoretical considerations. In this article, the safety goals, testing procedures and findings are presented on examples for different tunnel types: long alpine tunnels with bidirectional traffic and a short two-tube city tunnel with unidirectional traffic. 1 Introduction Tunnel ventilation systems serve to improve the safety of the tunnel users. In first order, they can ensure a sufficient visibility in the tunnel for safe traffic, and prevent concentrations of noxious gases from reaching critical values. However, the natural ventilation, mainly caused by the piston effect of the vehicles and by meteorological forces, is sufficient to ventilate most road tunnels. Therefore, the majority of ventilation systems is designed and used mainly to control the smoke movement in case of a tunnel fire. Since tunnel fires fortunately are not frequent, the ventilation system will be used only occasionally or even not at all. If systems are not tested regularly and thoroughly there is a good chance that they will not work properly when they are needed. Without a clear definition of safety goals and rigorous testing procedures to prove that those goals are achieved, the usefulness of the whole fire ventilation system must be questioned. The effect of improper fire ventilation systems was tragically visible on the tunnel fires in 1999 and 2001. Equipment performance tests in factories and on site are important means of quality assurance. However, they do not prove that the ventilation system works, just that the equipment meets the design criteria. The ventilation systems for the tunnel and for the escape routes are embedded in a complex system of incident detection, other safety equipment and control systems.

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Underground. The Way to the Future, 2013

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Geomechanics and Tunnelling, 2022

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