Deaths that occur when workers enter unused wells or tanks to clean them are not due to poisonous gases, as is widely believed, but because of carbon dioxide which is present at the bottom, says forensic expert P. Chandrasekaran.

Such deaths can be avoided by adopting simple measures like agitating the wells before entering them.

On Monday, two workers died of asphyxiation when the entered a tank in the city to clean it.

“Deaths in unused wells are common during summer. The failure to take simple precautionary measures is the cause for these deaths,” said Mr Chandrasekaran, a former director of the Forensic Sciences Department. He has several breakthroughs to his credit in his career, including the reconstruction of the belt bomb used by the suicide bomber in the Rajiv Gandhi assassination case.

Mr Chandrasekaran told The Hindu that he had investigated many deaths in wells and the culprit was not poisonous gases, but carbon dioxide, whose presence depleted oxygen and eventually caused asphyxiation.

“Organic materials deposit at the bottom of unused wells. Whey they start decaying, they release carbon monoxide. It is converted into carbon dioxide after it reacts with oxygen. Since carbon dioxide has high density, it stays at the bottom and inner layers of the wells and tanks and replaces the oxygen present there. When a worker enters the well to clean it, he dies only because there is no oxygen at the bottom,” he explained.

“We should lower a bucket full of water or soil inside the well and should stir the bottom vigorously. It will result in eviction of carbon dioxide and ensure presence of oxygen,” he said. This procedure should be followed by lowering a lit candle or a live fowl like a Japanese quail or a chicken into the well or tank.

“If the candle is put out or the fowl dies after some time, we can assume that carbon dioxide is present at the bottom. This is a time-tested practice still being adhered to in rural areas. Let us create awareness and avoid deaths,” he said. It is also a practice among coal miners to keep a canary bird with them. Signs of distress shown by the bird were a kind of early warning to them about the presence of toxic gases or depletion of oxygen.

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