TIANJIN — (CNN) When the wind blows in this Chinese port city, shards of glass still rain down from damaged buildings.
But many here are now more worried about a potential threat they can’t see: pollution from the hazardous materials that ignited Wednesday night at a chemical storage warehouse, sending a towering cloud of fire and smoke shooting into the sky.
“We are concerned that certain chemicals will continue to pose a risk to the residents of Tianjin,” the environmental group Greenpeace said. City residents shared similar fears on social media.
Despite reassurances from authorities, what might linger in the air or water is one of several big questions that remain unanswered in the aftermath of the blasts — one of which was the equivalent of more than 20 tons of TNT exploding.
At least 56 people have died and more than 700 are injured, some critically. Many others remain unaccounted for.
Tianjin officials say they are unable to give a detailed list of exactly what chemicals were being stored at the warehouse.
Gao Huaiyou, the deputy director of the city’s Work Safety Administration, said Friday the warehouse was only a temporary storage facility. Materials were kept there briefly when they arrived at the port and before they were transported elsewhere.
The warehouse site was destroyed by the explosions, he told reporters at a news conference, and managers of the facility have provided “insufficient information” about what was stored there.
Sodium cyanide, a highly toxic chemical that can rapidly kill humans exposed to it, was one of the materials, Gao said.
Greenpeace, citing a local monitoring station, said it believed other dangerous chemicals stored at the site included toluene diisocyanate and calcium carbide.
Gao said further investigation, including checks of customs records, would be needed to try to establish the types and amounts of the chemicals at the warehouse.
Wen Wurui, Tianjin’s environment protection chief, said Thursday that some chemical levels in the area were higher than normal but that they wouldn’t be dangerous to humans unless someone is exposed to them for long periods.
The wind has so far been helping by blowing fumes out to sea rather than toward the center of the city, said Feng Yinchang, a professor at Nankai University who spoke at the official news conference Friday.
The state-run news agency Xinhua issued a warning telling people not to spread rumors about the situation, including the air quality in Tianjin and Beijing, which is about 110 kilometers (70 miles) away. Some social media posts about the disaster were deleted from platforms in China.
Officials say they have blocked off sewage pipelines that run from the port industrial area where the warehouse was located into the sea in an effort to prevent polluted water flowing out.
But Greenpeace warned that the possibility of rain Friday could pose more challenges by setting off reactions and washing chemicals into the ground. Toluene diisocyanate and calcium carbide both react violently with water, it said.
Liu Yue, a 25-year-old who lives about 4 kilometers from the blast site said she and others in her neighborhood were only drinking bottled water amid concerns about contamination.
“I’ve told my parents not to drink tap water,” she said.
Tianjin authorities say they have set up 17 monitoring stations for air and five for water. More than 200 chemical specialists from the military have been sent in with detection devices, Xinhua reported.
Footage on state television appeared to show some smoke continuing to rise from the area on Friday.
Firefighters have been using foam to try to extinguish the remaining fires at the blast site, officials said.
Zhou Tian, chief of Tianjin Public Security Fire Bureau, told reporters Friday evening that the flames have been largely extinguished on site, but some smoke remains.
Some debris has been cleared to make a path for firefighters to gain access to the main blast area, he said.
Firefighters have prepared 600 tons of sand to be used to put out the remaining fires, he added.
Fire officials say hazardous chemicals stored at the warehouse were ignited by fire. But the cause of the fire has yet to be determined.
Officials didn’t address the issue directly at the news conference Friday morning.
Executives from Rui Hai International Logistics Co., the company that owned the warehouse, have been taken into custody, state media reported Thursday.
Authorities in Tianjin appeared to have been concerned recently about the handling of hazardous materials at the port.
A notice posted by the Tianjin Administration of Work Safety on its website last week said city officials held a meeting with executives of more than 20 companies that handle dangerous chemicals at the port.
The agency’s director urged the executives to carry out safety management, the notice said.
It’s unclear how much higher the death toll might rise.
Authorities have said that 21 firefighters are among the 56 people confirmed dead.
One was rescued Friday from the rubble, Xinhua reported, leaving 18 still missing.
Dozens of employees of the Tianjin Port Group Co. are also unaccounted for, Xinhua reported late Thursday.
Of the 721 people hospitalized, 25 are in critical condition and 33 in serious condition, officials said Friday.
Although the toll is grim, it could have been a lot worse if the blasts had struck during the day, when more people would have been working in the port area.
The district where the warehouse was located is thinly populated and situated roughly 40 kilometers (25 miles) from the center of Tianjin.
Tianjin is a sprawling municipality of more than 13 million residents, but the China Earthquake Networks Center said that slightly under 90,000 people lived within a 5-kilometer radius of the blast site.
More than 6,000 people have taken shelter in a dozen nearby schools and three apartment compounds, said district official Zhang Ruigang, after their homes were damaged by the explosions’ shock waves.
Amid a camp of tents on the grounds of one school, Tao Shunfeng recounted driving a truck through the port when the explosions struck, shattering all the vehicle’s windows.
He said he was now worried about the air and planned to leave Tianjin with his wife and child to return to his home province of Henan.
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