Transit tunnel emergency ventilation systems must effectively control smoke and toxic fumes from an in-tunnel fire while simultaneously be quiet enough to allow passengers within the tunnel to understand and respond to emergency communications. As transit systems are often located in urban areas and the emergency ventilation systems undergo regular testing, noise from the tunnel exhaust shafts can also adversely impact nearby sensitive land uses in the community. This paper will describe the assessment of in-tunnel and community noise levels generated by tunnel emergency ventilation systems throughout the transit system of a major United States city. Topics that will be discussed include the noise criteria established for the system, the assessment methodology to predict in-tunnel and outdoor noise levels, the selection of fan silencers and acoustical panels to control noise, and noise compliance measurements completed after the ventilation system upgrades were installed. The assessment generally followed ASHRAE guidance for ventilation noise predictions; however, given the large size and complex geometry of the ventilation shafts and plenums, alternative calculation methods and the ODEON room acoustics model were used as well.
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