Authorities found at least 15 hazardous chemicals in a groundwater sample collected from the APCB Electronics Co factory, which was gutted by fire in Ayutthaya’s Bang Pa-in Industrial Estate on Monday.
A source in the Industrial Works Department said authorities had collected the water sample for inspection to determine the cause of the fire.
Among the hazardous chemicals found, cyanide was the most dangerous. But the authorities have been unable to link it to the cause of the fire.
They are looking for flammable chemicals or chemical residues that could have sparked the blaze.
It was not clear whether the tainted water is affecting the drinking water in the area.
The fire broke out at the five-storey factory about 11.30am on Monday and sent more than 900 workers fleeing for their lives.
The blaze, which started on the third floor where chemical solutions for cleaning electronic circuits and parts were stored, was put out nearly seven hours later. But it erupted again about 11pm.
The second to fifth floors were all engulfed in flames when firefighters and police arrived back at the scene.
The flames spread quickly, fanned by a strong wind, before the fire was brought under control about 1am yesterday, said Mr Udomsak Khaonoona, head of the Ayutthaya provincial disaster prevention and mitigation office.
Mr Udomsak said forensic officials and police are investigating the initial cause and why it rekindled after having been extinguished.
Officials from the Industrial Works and Disaster Prevention and Mitigation departments will inspect areas around the factory, Mr Udomsak said.
An initial inspection found the fire-gutted building had not collapsed, but there were some cracks in the walls.
The factory produces electronic circuits and parts and is owned by a large-scale Thai, Taiwanese and Chinese joint venture.
Authorities yesterday sealed off the site and declared the fire-gutted electronics factory a danger zone.