Scanners will be installed at both ends of the Karnaphuli tunnel in Chattogram to make sure that vehicles carrying flammable goods cannot use the underwater structure.

"Vehicles carry flammable goods and combustible materials will not be allowed to access the tunnel ... ," Harunur Rashid Chowdhury, project director of the Bangabandhu Sheikh Mujibur Rahman Tunnel project, told The Daily Star.

Carrying of inflammable goods and combustible materials like LPG cylinders, gas, kerosene oil, hydrogen gas and all kinds of fuel through the tunnel would not be allowed on safety grounds.

"We have decided that each vehicle will be scanned before they enter the tunnel to ensure safety and security," the PD said.

The construction of the 3.32km tunnel under the Karnaphuli river is scheduled to be completed by December at a cost of Tk 10,374.42 crore.

Installation of scanners was not part of the project.

Asked if the project cost would increase for the inclusion of the scanners, Harunur said they would try to keep the expenses within the total project cost.

Project officials said 91 percent work of the first ever underwater tunnel in South Asia has been completed until Friday.

They said despite some concern over possible congestions due to scanning of vehicles, the decision to install scanners was made with security in mind.

Bangladesh Bridge Authority (BBA) officials had expressed concern that the scanning of vehicles might create tailbacks at both ends of the tunnel, which may ultimately discourage transport operators from using the structure, said an official with knowledge of the project.

However, after being apprised of the problem, all authorities concerned opined in favour of the scanners, said the official.

Civil engineering work of the project is almost at the final stage. Electrical and mechanical works, including installation of lamps, fireproof plates, decorative plates, pumps, power supply and ventilation system, are now going on in full swing, according to the monthly progress report of the project.

The work on two out of the three cross passages (connecting two tubes) has already been completed and the work on another has seen 50 percent progress.

The tunnel is being constructed at a depth of 18 to 31 meters under the Karnaphuli and the length of the main tunnel is 3.32km. The length of each of the two tubes, having four lanes, is 2.45km.

There will be a 5.35km connecting road at the western and eastern ends of the main tunnel and a 727 metre flyover at the Anwara end.

Speaking to reporters in Chattogram on July 29, Cabinet Secretary Khandkar Anwarul Islam said, "A tube of the tunnel will be opened to traffic at the end of October or early November and another one will be inaugurated in December."

However, the project director said it was not possible for them to say when the tunnel will be inaugurated. "We are working to the complete the project within the deadline of December."

He said a pre-commissioning of the tunnel will be done on completion of the construction.

In November 2015, the Executive Committee of the National Economic Council (Ecnec) approved the multi-lane road tunnel project at a cost of Tk 8,446.64 crore. The cost was later increased to Tk 10,374.42 crore.

The Exim Bank of China is providing Tk 5,913.19 crore at an interest rate of two percent, while the Bangladesh government is providing the rest of the fund.

The much-talked-about tunnel will connect the southern and northern parts of the Chattogram district, opening up economic opportunities. It will also be used as an alternative road to Cox's Bazar, Teknaf and Matarbari.