The National Freeway Bureau yesterday said tunnel ventilation fans in the Hsuehshan Tunnel were working normally at the time of a bus collision and ensuing fire last week, in which two people were killed and more than 20 injured.
The Chinese-language Apple Daily reported yesterday that 13 axial tunnel ventilation fans, out of a total of 40 in the tunnel, were not operational at the time of the accident, adding that the smoke was only vented 37 minutes after the fire was put out, which some have said was too slow.
Bureau Director-General Tseng Dar-jen (曾大仁) yesterday confirmed that 13 axial tunnel ventilation fans were not operational, as five malfunctioned fans were being repaired and eight had been temporarily stopped for maintenance work.
The bureau said eight fans at the No. 3 ventilation shaft were shut down for maintenance work and a water diversion project caused by water seepage problems.
However, the bureau said the ventilation system had been -adjusted to ensure normal operations in the tunnel during maintenance work.
Based on the original design, the ventilation fans have a backup system of about 50 percent, meaning full operations can be sustained as long as more than half of the fans are working, Tseng said
“The fans create the necessary wind field and in the recent accident that made it possible for people to escape,” he added.
The accident occurred at the 26km marker on the southbound side of the tunnel, 2.1km from the south exit, with the No. 3 ventilation shaft about 1.4km north of that position.
“If the smoke was to be vented from the No. 3 ventilation shaft, the wind would have had to be sucked back in the opposite direction, which the ventilation system basically prohibits,” Tseng said, adding that was why smoke was mainly vented from the tunnel’s south exit after the accident.
The bureau’s Northern Region Engineering Office director Hsu Cheng-chang (許鉦漳) said the tunnel’s ventilation system was designed to create a wind field that flows in the same direction as the cars, ensuring there is always clean air behind an accident and thereby making it easier for passengers to escape the scene.
“We urge those who find themselves behind an accident in the tunnel to make their way in the opposite direction of the traffic flow and cars in front of the accident to keep moving forward and exit the tunnel as quickly as possible,” he said.
Maintenance work on eight fans at No. 3 three shaft should be completed in September and three of the five fans being repaired will be operational by tomorrow, Hsu said, adding that repair work on the remaining two fans will take two months.