In this study, the effects of the jet fan speed, heat release rate and aspect ratio on smoke movement in tunnel fires have been investigated. The jet fan speed was changed from 6.25 (25%) to 12.5 m/s (50%), 18.75 m/s (75%), and 25 m/s (100%). The heat release rate was set up from 3.9 to 6 MW and 16 MW, the aspect ratio was changed from 0.6 to 1 and 1.5, respectively. The lower the jet fan speed is, the longer the smoke back-layering length is. With a higher velocity, the smoke tends to move out of the tunnel quickly; however, smoke stratification also occurs, and this reduces visibility. This could make it difficult for people to evacuate. With a higher heat release rate, the smoke tends to move far away from the fires quickly when compared with other cases. Additionally, the higher the heat release is, the longer the smoke back-layering is. Finally, with a higher aspect ratio, the smoke back layering length in the tunnel is also longer. The smoke layer thickness is also larger than in other cases. The correlation of velocity, heat release rate and aspect ratio has been investigated to avoid the smoke back layer length in tunnel fires.

The aspirating smoke detector (ASD) is one of the most critical pieces of equipment for detecting smoke in a protected area when a fire occurs. It has more advantages than a conventional smoke detector because it can be used in extreme conditions, such as cold storage facilities or hot aisle containment areas. ASD uses a fan to draw air from the protected area into the pipe network system via pipe holes. The sucked air is transported into the sensing chamber to detect smoke. If the obscuration in the sensing chamber is greater than the setpoint, the ASD will sound an alarm so that people realize there is a fire. For this reason, investigating the effect of the pipe hole network on obscuration in the ASD is critical. In this study, a Pipe Hole Network Program was developed to consider the pipe flow parameter. A numerical study based on the program and an experimental study was performed. The results showed that the numerical results had the same trend as the experimental study. The further the location of the fire source was, the lower the obscuration was. In addition, the correlation between the obscuration parameter and the fire source distance was also derived. It could be used to predict the fire source location in the aspirating smoke detection system.