The fatal CentralWorld blaze on Wednesday started on the B2 basement floor of its old and possibly defective back-office building where dry sediment in a wastewater treatment facility might have caught fire, according to officials.
Experts made the assumption after inspecting the 16-storey back office of the CentralWorld shopping complex in Pathumwan district.
Teerayut Pumisak, deputy director for disaster prevention and mitigation of the Bangkok Metropolitan Administration, said the fire started on the B2 floor, an enclosed space for storage of fire-fighting pumps, a wastewater treatment facility and electric equipment.
"A material that caught fire was dry waste sediment. Fire from it could be as hot as 800 degrees Celsius," he said.
The fire sent heat and gas into three big ventilation pipes that ran upward to the eighth floor where they bent to move air out of the building. The curved pipes on the eighth floor blocked the passage of heat and smoke and were not heat-resistant. They finally collapsed and the fire and smoke spread on the eighth floor where there were lots of flammable materials such as chairs, desks and furniture, Mr Teerayut said.
Amorn Pimanmas, secretary-general of the Council of Engineers, said oil stains from cooking might also clog the vent pipes and block smoke from being emitted out of the building easily.
Pichaya Chantranuwat, secretary-general of the Engineering Institute of Thailand, said officials had yet to locate where exactly the fire started on the B2 floor. The plan of the building showed it was an old building constructed when the shopping complex was called World Trade Centre.
The ventilation pipes were not built to reach the rooftop of the building because the old building was designed that way and had some weak points, he said.
Mr Pichaya said the two men who died were heroes because they could have easily fled the eighth floor. Instead, they went inside to try to put out the fire which later blocked their exit, forcing them to jump off the floor.
The structure of the eighth floor was complicated and obstructed fire-fighting efforts, he said.
Pathumwan district chief Pinit Arayasilpatorn said the 80-sq m B2 floor and the 400-sq m eighth floor were closed while other parts of the building could be opened soon. The eighth floor was a recreation area for staff, he said.
Noppadol Chaipanya, public works director of the City Hall, said the two floors would be closed until their plans were improved.
Siriwat Chaichana, adviser to the Engineering Institute of Thailand, said the fire was extinguished quickly and the structure of the building was not affected.
The management of Central Pattana, the operator of the shopping complex, said the company would do its best to take care of the injured people and the families of the dead victims. The fire killed two people and injured 20 others.
Shop operators wait in front of the closed CentralWorld shopping complex to enter the mall and check the damage at their shops on Thursday. (Photo by Apichart Jinakul)