Unless you're from Bhopal, India or have other good reasons to remember it, you'll probably have to do an online search for the details. In short, years ago, some chemical plant in Bhopal, India sort of exploded and pumped several tons of poisonous gas into the town. Many thousands died. 600,000 people were affected.  From The Atlantic…

"Bhopal: The World's Worst Industrial Disaster, 30 Years Later"

Bhopal – Thirty years ago, on the night of December 2, 1984, an accident at the Union Carbide pesticide plant in Bhopal, India, released at least 30 tons of a highly toxic gas called methyl isocyanate, as well as a number of other poisonous gases. The pesticide plant was surrounded by shanty towns, leading to more than 600,000 people being exposed to the deadly gas cloud that night.