The guideline ‚Ventilation of road-tunnels’ by the Swiss Federal Roads Authority (22.12.2004 with clarifications dated on 31.07.2006) describes the requirements to the layout of the fire ventilation and in particular of jet fans for the handling of longitudinal airflow.
The controlling of jet fans requires high expenses for the measurement and closed-loop control. The handling of the longitudinal airflow is depending on the accuracy and reliability of the airflow measurement which is known to be very sensitive. The use of wrong measurements may have disastrous consequences.
In many existing tunnels which have to be adapted to the new safety standard, jet fans can not be installed because of lack of space, or they would require expensive changes of the construction.
Therefore, alternative ventilation concepts for the handling of the longitudinal airflow have to be analysed, e.g. the use of existing (semi-)transversal ventilation equipment, point injection in the tunnel or point extraction from the tunnel, saccardo-nozzles, air curtains and other concepts. The handling of the longitudinal airflow should be efficient, reliable and simple to control.
The project has the following objectives:
- Contribution to higher safety in road tunnels
- Evaluation of different ventilation concepts to handle longitudinal airflow in road tunnels in order to limit smoke spreading in case of fire by using ventilation systems with and without smoke extraction.
- Focus on overall systems (ventilation equipment, measurement devices, control system). Comparison of different concepts regarding efficiency, feasibility, costs (investments, operation and maintenance), reliability, experiences in practice etc.
- Determination of suitable measures to handle longitudinal airflow in existing and new road tunnels.
The following work is planned:
- Analyseis of literature and existing studies on air curtains, Saccardo nozzles etc., co-operation with international research centers and compilation of the possible methods;
- Summary of own experiences with selective insufflation, extraction and use of semi-transverse ventilation (supply) and cross ventilation in existing projects in Switzerland and abroad;
- Comparison of all methods with different dimensional simulation calculations;
- Examination of selected method with three-dimensional simulation calculations;
- Test of selected processes with ventilation systems in existing road tunnels (in cooperation with the tunnel operators);
- Comparison of measurements with calculations;
- Summary of findings and recommendations in a final report.
Under the project, several ventilation principles were examined for the purpose of controlling
the longitudinal air flow in a road tunnel. In addition to jet fans, which are commonly used in Switzerland, the application of the following was examined: semi-transverse/transverse ventilation, point injection (in particular as Saccardo nozzles), air extraction from the tunnel, air curtains and mechanical curtains.
The different methods were qualitatively described and compared with each other. This was conducted by representing the physical principals, mathematical descriptions and with examples from practise.
A qualitative comparison was made regarding:
- Impact and effectiveness
- Feasibility (for new and existing tunnels)
- Civil costs (ventilation stations, ducts, niches, etc.)
- Costs of electro-mechanical equipment (fans with ducts and dampers, power supplies, instrumentation, control system)
- Cost (investment, operation and maintenance)
- Genuine eperience from opexration of such systems
As the most suitable method, jet fans and Saccardo nozzles were identified. While for jet fans extensive theoretical studies and experience is available, in recent years there has been little application of Saccardo nozzles at least in Switzerland.
Therefore, a focus of this research project was on the study of Saccardo nozzles. 2D and 3D simulations investigated the influence of local flow effect. Consequently, correction factors for the (known) one-dimensional design calculation were established.
In an existing road tunnel, measurements with a Saccardo-nozzle model were performed. Thus, the simulations were by and large confirmed. Moreover, practical know-how for possible mplementations in refurbishment projects was acquired.
Enhancing of safety in tunnels