The fumes spread from a container containing 2-Chloro-5 chloromethylpyridine, which is used in insecticides and pesticides. The chemical was imported from China and was to be taken to Sonepat in Haryana.
The students of Rani Jhansi School and Government Girls Senior Secondary School, run by the city administration, were rushed to nearby hospitals as they complained of irritation in eyes and breathlessness.
The Delhi government has ordered a magisterial probe into the incident. Police has registered an FIR in the matter under various sections of IPC and the Environment (Protection) Act.
The southeast district administration issued the show cause notice to the Customs Department and the Container Corporation Of India Ltd (CONCOR), the custodian of the depot, asking it why the depot should not be shut down.
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"We will take strict action in the matter as hazardous chemicals were stored in the depot ... We have issued a show cause notice to CONCOR and the Customs Department seeking their reply as to why the depot should not be shut as it is unsafe because it is situated near schools," B S Jaglan, district magistrate (southeast), said.
A CONCOR spokesperson said it is a cause of concern and they are looking into the leakage. "We will cooperate with the probe," he said.
He said the depot is like a port where the imported material arrive and their employees do not have access to the "bonded" area, where the containers are kept.
"The chemical was imported from China by a company which deals in agricultural products. The container belongs to the shipping line," he said.
"The spill was noticed by some people in the inland container depot. We threw a lot of mud and caustic soda around it to nullify its effect. Whatever was left was carried away by the wind which is unfortunate," he said.
"Tughlakabad area is safe now. A National Disaster Response Force team also visited the consignee factory at Sonepat... All containers have been emptied and washed," the force's Director General R K Pachnanda said.
He said the driver noticed the leakage first when he stopped for tea outside the inland container depot at around 3.30 AM today. However, the police and the fire department said they were informed about the incident at around 7.30 AM.
He did not pay much heed to the foul smell since he has not slept properly and was feeling dizzy.
An NDRF official said there were 80 drums in the container and the chemical leaked from three-four of them.
The driver unloaded the drums in Sonepat. It is expected that the chemical spilled at the ICD when the loading/ unloading of the containers was taking place.
"It was in liquid form and vaporised when it came in contact with the air," another officer said.