A chemical workshop and warehouse in Thuong Thanh District, spanning over 270 m2, caught fire on June 30, followed by multiple explosions. Several chemical containers, each with a capacity of around 200 liters, exploded in the blaze. With no casualties, the cause of the fire has yet to be determined.

The Hanoi Department of Natural Resources and the Environment had said the exact types and amount of chemicals that either burned or leaked out into the environment has yet to be tested, as it could not get in contact with representatives of Cuong Viet Trading and Production Company, which manages the warehouse.

Air analysis by the Military Institute of Environment and Chemistry and the Center of Natural Resources and Environment Monitoring on July 1 showed the presence of numerous flammable hydrocarbons, including toluene, n-Butanol, acetone, methanol and benzene, near the fire site. Notably, toluene levels in the air were up to 17.53 times higher than normal standards, analysis showed.

Even two days after the fire, toluene and methanol could still be detected in the air surrounding the site, still at levels much higher than normal, according to the institute.

As of Wednesday, over 20 personnel from Urban Environment Company Urenco 10 were still cleaning up debris, collecting chemicals and cleaning up water left from firefighting efforts. The entire site has been covered with sheets to prevent chemicals from spreading further. Hanoi High Command has also decontaminated the area.

Toluene, an aromatic hydrocarbon, is a liquid that easily gasifies and could poison humans if exposed to high doses, said Nguyen Duy Thinh, a professor at the School of Biotechnology and Food Technology under the Hanoi University of Science and Technology. Poisoning symptoms include lung and liver damage, headaches, nausea and loss of consciousness.

"When burned, combined with the dry and hot weather, this substance quickly gasifies and spreads over a large area, which quickly lowers its concentration in the air. As such, there would be no lasting impacts around the fire site," said Thinh, adding locals in the area should still be cautious and wear masks and protective glasses when going outside.

Cuong Viet Trading and Production Company was licensed by the Hanoi Department of Industry and Trade to buy and sell eight types of chemicals: Isopropanol, toluene, acetone, ethyl acetate, n-butyl acetate, methyl ethyl ketone, xylene and ethylbenzene. The total mass of chemicals approved for sale was 250 tons a year.