It all points to accumulated gas
Accumulated gas is the likely cause of Tuesday's explosion that left at least 20 people dead and over 100 injured on North South Road in the capital.
There were two possible sources of the gas that got trapped, experts in police said yesterday, requesting anonymity.
Seven days before the blast, a pipeline for cooking gas was repaired next to the seven-storey building in Siddikbazar, they said after visiting the site, adding that gas might have escaped through a leak and accumulated in a confined space.
Another possible source of gas could be a poorly plugged gas pipeline to a restaurant on the ground floor of the building, said the experts. The gas supply to the restaurant was recently disconnected.
A leak from the plug could have created a gas chamber underneath the building, they said.
Rescuers also reported that after the explosion, members of the government's gas transmission authorities went there and replaced the blown-off plug.
Maj Moshiur Rahman, chief of the Bomb Disposal Unit of Rab, also said this gas line could be a possible cause for the explosion.
However, Titas Gas Transmission and Distribution Company Limited said there was no evidence that gas was the cause of the explosion.
"The gas riser device in the building is intact. The evidence we collected using a gas detector also does not indicate it was an explosion due to gas," said Salim Miah, director (operations) of the company.
The explosion rocked Siddikbazar, a major commercial area in the capital, around 4:45pm. It happened in the basement of the seven-storey building. The top four floors are residential while the rest are commercial.
Rabiul Islam, president of Bangladesh Pipe and Tube Well Merchants Association, said that there were three sanitaryware shops on the first floor and one in the basement.
The blast destroyed almost everything on the first three floors and debris covered part of the street in front.
Glass windows and fittings of a five-storey building next to it were also damaged.
Safayet Hossain, a storekeeper in the area, said the explosion felt like an earthquake.
"I saw 20-25 people lying on the road. Most of them were bleeding. They were crying for help. Some people were running around in panic," he told The Daily Star.
This is the second such incident in the capital within a week. On Sunday, three people were killed in a blast at a building near the Science Lab intersection.
Law enforcers and army personnel ruled out the possibility of any subversive act as they did not find any evidence of explosives at the scenes.
The bodies of 16 were handed over to the families early yesterday.
On Tuesday, the authorities said 17 people had died in the explosion. Yesterday, firefighters recovered two more bodies from the basement and another person died of injuries at a hospital.
Ten of the injured were admitted to Sheikh Hasina National Institute of Burn and Plastic Surgery in critical condition. Twenty others are being treated at the Dhaka Medical College Hospital.
Two people are reported missing.
The rods inside a column of the damaged building were seen sticking out.
Firefighter suspended rescue operations at 8:00pm on Tuesday after noticing cracks in the loadbearing columns. They resumed it on a small scale yesterday morning by removing debris and pumping out water from the basement as the blast caused a leak in a reservoir. They suspended operations around 7:15pm declaring the building highly risky.
Officials of the Rajdhani Unnayan Kartripakkha also labelled it highly risky.
Dhaka Metropolitan Police Commissioner Khandker Golam Faruq said experts from the Counter Terrorism and Transnational Crime unit (CTTC), Criminal Investigation Department, and the army visited the spot and found no evidence of explosives.
CTTC experts said gas might have accumulated in the underground water tank resulting in the explosion. Besides, too much biogas in the septic tank could also cause a blast, they added.
A leaky gas pipe could have created a channel underground and gas might have accumulated gradually. It was somehow ignited, causing the blast, they added.
There is also the likelihood that a leaky sewer pipe turned part of the building into a gas chamber, they said.
Rahmat Ullah Chowdhury, the in-charge of CTTC bomb disposal team, said, "The gas chamber exploded following a spark [that ignited it]."
He added, "No traces of explosives or fragments of IED circuits were found."
Besides, the smoke was not black or of any colour that would suggest an explosive attack, and the bodies recovered bore no splinter wounds, he added.
Rab Bomb Disposal Unit chief Maj Moshiur Rahman also said gas was the most likely cause.
"But we don't rule out other possibilities. It could be triggered by something else," he said.
Mohammad Harun Or Rashid, additional commissioner of the Detective Branch, said the building was constructed in 1992. But the top floors were built years later.
"The garage is no longer a garage. Even the owner cannot say where the septic tank is," he told a press briefing.
He did not give a direct answer when asked whether the caretaker of the building was picked up.
The detectives are interrogating the owner, shop keepers, and others as they are conducting a shadow investigation, he said.
Family members of Abdul Motaleb Mintu, owner of a sanitaryware shop at the building, said DB officers picked him up from the Dhaka Medical College Hospital around 3:00am yesterday. He was at the hospital looking for a missing employee.
Mintu's cousin Anwar Hossain told The Daily Star that he was with Mintu when detectives took him.
But Mashiur Rahman, deputy commissioner (Lalbagh) of DB, said no one was picked up.
The deceased include: Mominul Islam, 38; Nodi Begum, 36; Mainuddin 50; Ismail, 42; Abdul Hasim, 34; Ishaq Mridha, 35; Rahat, 18; Al Amin, 23; Nazmul Hossain, 25; Obaidul Hossian Babul, 55; Abu Zafar Siddique, 34; Monsur Hossain, 40; Akriti Begum, 70; Idris Mir, 60; Hridoy, 20; Nurul Islam, 45; Momin Uddin Sumon, 48; Robin Hossain, 20; and Hafez Musa Haider, 46.
Police filed an unnatural death case with Bangshal Police Station, said Inspector Kamrul Hasan Kamal.