"This is a clear case of spontaneous combustion," said environmentalist Sumaira Abdulali, who visited the spot with TOI. Burning ash collected from the site was sent for chemical analysis in a local lab. It found the presence of sulphur, which is highly toxic. "Sulphur oxides (SO2, SO3), formed when sulphur combines with oxygen, are also very toxic," said Abdulali. She pointed out that smoke was coming out of the area around what appeared to be a water pipe. "It is possible that the water is combining with sulphur to create toxic fumes and sulphuric acid," she added.

At present, over 1.5 lakh metric tonnes of coal are lying in the open at seven storage sites. The site where smoke was seen rising out of the coal, is directly in front of Hindustan Petroleum's Mazgaon Lube Plant No 2.

TOI in a series of reports earlier this year has highlighted the extent to which the coal has affected the environment and the health of those living around it.

Residents in the area said smoke rising out of the coal is a common occurrence. Inhaling smoke causes respiratory problems. Contamination of chemicals with water is very bad for the health and is hazardous," said Dr K D Kapadia, former president of Indian Medical Association (Mumbai), currently a part-time doctor at the Indian Maritime Association campus, a stone's throw from the coal heaps.

"Any open combustion is banned in all cities as it causes air pollution. Burning coal is thus an offence. Allowing spontaneous combustion unchecked will lead to the arrest of the persons responsible in any self-respecting administration," said retired vice-admiral I C Rao, who, along with banker Meera Sanyal, had petitioned the Bombay high court seeking to prevent the Maharashtra Pollution Control Board from renewing the 'consent to operate' to Mumbai Port Trust (MbPT) for handling coal, which expired in September 2014. The matter is at present pending with MPCB and MbPT continue to handle coal.

This health hazard is not limited to Sewri, since air pollution is a hazard for the entire city. "Indian cities already have amongst the worst air quality in the world. We are only making matters worse by having such large quantities of coal lying in the open in the midst of the city. We have some of the highest levels of respiratory diseases in the world," said Abdulali.

Incidentally, Rao and Sanyal raised the matter of spontaneous combustion in their court petition. In response to a Right to Information query filed by Rao, the port trust had denied that any instance of spontaneous combustion had occurred in 2012-13 and 2013-14. In a submission to the pollution control board in November 2014, the port trust said, "It is reiterated that not only is the coal stacked safely, there are sprinklers installed which periodically sprinkle water to avoid situations such as spontaneous combustion."

When contacted, port trust authorities said combustion was a normal phenomenon and they had it under control, adding that smoke from the coal heaps was not expected during the monsoon.