During the early hours of 3 December 1984 the world's worst industrial accident unfolded in the Indian city of Bhopal.
Poisonous gas escaped from a chemical plant and killed 3,000 people, according to official estimates. Other estimates put the number at between 8,000 and 10,000.
Around 50,000 suffered permanent disabilities, and more died later.
Many people lived in shanty towns built alongside the factory and thousands more lived nearby in the old city.
There was no contingency plan for evacuation in the event of an emergency.
Poor sales had led the company to cut costs, scale back production and lay off around a third of the workforce.
Safety systems had also been cut.
The main ingredient of the pesticide made at the plant was a chemical called methyl isocyanate or MIC.
MIC is one of the most toxic and lethal substances known to humans.
Safe storage requires it to be kept cool and isolated from water, which can trigger a violent runaway reaction creating heat and a deadly gas.
A worker cleaning out pipes with water sparked the disaster.
He did not use a basic but vital piece of equipment to isolate sections of pipe.
Water got into the tank where the MIC was stored, raising the temperature to over 200 degrees Celsius (392F), creating the lethal gas.
Several safety systems failed or were not working.
Bhopal was asleep when the gas struck.
Simple advice to move upwind or stay indoors and seal doors and windows with damp cloths could have saved thousands but Union Carbide had not told people what to do if there was a leak.
Crowds of terrified people fled.
Bhopal's hospital was overwhelmed, lacking information about the gas or antidote.
Union Carbide accepted "moral responsibility" for the disaster. It later blamed sabotage by a disgruntled worker.
After a legal agreement the firm provided victims with compensation averaging $500 (£300).