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Background & Objectives: Different methods can be used for ventilation of tunnel during construction. Each method has advantages, limitations, and disadvantages that should be considered in selection of methods. Inefficient ventilation can lowered production rate and provide undesired work conditions for employees. This issue is critical in gaseous tunnels and may imperil the workers lives and the whole project. This paper presents a series of guidelines for selection of ventilation system, optimal implementation, and aspects of ventilation system design in gaseous tunnels based on common ventilation standards. Methods: Common ventilation systems in tunnels during construction were compared for selection of Alborz tunnel ventilation system. Air-supply ventilation system was selected as the best design. Whereas air-supply ventilation system may be applied in different forms, six distinct designs were compared for Alborz tunnel. In order to determine tunnel ventilation capacity, air volume required was calculated based on different criteria.Air volume required for diesel equipment was considered as the air requirements of tunnel ventilation. Considering advantages, disadvantages, and limitations of the small and large diameter channel applications, ventilation system calculations were conducted for the diameters 100, 140, and 180 cm to select optimum size. Results: The results from comparison of different ventilation variants showed that using two parallel jet fans on tunnel surface in a joint canal (140 cm) is the most appropriate design for tunnels with these characteristics. Conclusion: Poor ventilation is a critical factor in deep underground and gaseous tunnel drilling and improper ventilation may substantially affect the work environment, life, and production rate.

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Background & objectives: Legionella is a hard to grow gram negative bacterum responsible for Legionnaires' disease which is a severe form of pneumonia and can be fatal. These bacteria can grow on air conditions and cooling systems and may causes epidemics. Due to resistance  to chlorine and other disinfectants this study aimed to identify and control these bacteria in air conditions and cooling systems.
Methods: For this cross-sectional study, samples were collected from air conditions and cooling systems of Kerman University of Medical Sciences. A total number of 310 samples were taken from water tanks of coolers, cooling and air condition systems of hospitals, clinics,education and student ceters,  offices, and dormitores. Samples were transferred to the laboratory  and concentrated prior to washing with acidic buffer. They were inoculated on to BCYE, BMPA and MWY media. Samples were incubated in 2.5% of CO₂ and water and plates were examined within two weeks. Results were reported as percent and average. Comparisons were done with chi-square test, ANOVA and t-test. Data were analyzed using SPSS version 20.
Results:Of the 310 samples, %22.26 was infected with Legionella bacteria, of which %12.9 was related to  water cooling systems. Infection with Legionella bacteria was significantly high in health centers and water coolers. The most prevalent bacteria was Legionella pneumophila.
Conclusion:There are infection with this bacterium in some of the cooling systems in Kerman University of Medical Sciences and it is nessessary to consider control strategies.