It is midnight on December 3, 1984. As people slept in the capital city of Bhopal in Madhya Pradesh, India, pressure from a reaction in a chemical tank at a nearby Union Carbide (India) Ltd. pesticide plant pumped large amounts of the highly toxic gas methyl isocyanate and other hazardous chemicals into the atmosphere.

That cloud of chemicals rapidly descended upon the city, exposing hundreds of thousands of people in the vicinity to its lethal effects. By morning, thousands of men, women, children, livestock and vegetation had succumbed.

The death toll has been hard to determine in part because of poor record keeping and a lack of proper birth documentation. Organizations have put the number of immediate deaths at around 3,500, while others calculated a death toll of 8,000 to 10,000 within the first few days, many from cardiac and respiratory arrest.

Since then, some 20,000 people have died as a result, according to Greenpeace. Health effects have continued to plague survivors, with about 20 to 30 people reportedly dying of gas-related injuries each month, based on 2006 figures from the International Campaign for Justice in Bhopal.

U.S. chemical company Union Carbide Corporation, which owned half of the pesticide plant (Indian financial institutions and private investors held the remaining stake), was taken to task following the disaster, and in 1989 entered into a $470 million legal settlement with the Indian government. The question of compensation remains contentious to this day.

In 2001, U.S. chemical major Dow Chemical Co. acquired UCC and the spotlight shifted. Today, on the anniversary of the Bhopal disaster, Dow Chemical is facing public outrage over its high-profile sponsorship of the London 2012 Olympics, prompting protests this week in India that called for the Midland, Michigan-based company to be excluded from the event's list of sponsors.

From India to the U.S., and now to the U.K., the impact from the Bhopal disaster is far-reaching as survivors continue to battle health issues, families of victims fight to keep the memories of their loved ones alive, and companies and cities face the fallout from what has been called the worst industrial disaster on record.

Here's a look back at one of the most devastating -- and most defining -- moments in our history of industry.