Saroj Bhattacharjee, 81, calls it the “biggest trauma” of his life. The Edmonton man was a maintenance engineer at Union Carbide in Bhopal, India, in 1984, when the toxic gas methyl isocyanate leaked from a storage tank.

Just after midnight as poisonous plumes of smoke wafted through the Indian city of Bhopal four decades ago, Gas Devi was born, gasping for every breath.

Considered the world’s worst industrial incident in modern times, the Bhopal gas tragedy was a chemical accident at a pesticide plant in Bhopal, Madhya Pradesh, India.