According to CEA norms, power plants with less than a week's stock are deemed 'critical' and stocks less than four days considered 'supercritical' for non-pithead units.Ironically, the genesis of the problem lies in the improved supply situation. As TOI first reported reported on February 22, power stations had drawn down their coal stockpiles by 50% to reduce inventory costs as timely supply became the new normal. Total stockpile at plants reached 39 million tonnes at the beginning of 2016-17, with several plants showing coal stock for 50-60 days, while the average stock exceeded 25 days. "This led to pithead stock at Coal India piling up, prompting the company to prune production. Then the Dhanbad-Chandrapura railway line was closed due to concerns over caving in and supply quotas were shifted to CCL.

Source: Times of India August 25, 2017 23:15 UTC