The Methyl Isocyanate Release from the Union Carbide Plant at Bhopal on the Night of 2-3 December 1984

The Union Carbide India Limited pesticide plant in Bhopal, Madhya Pradesh, had manufactured the insecticide carbaryl using the intermediate methyl isocyanate (MIC) since 1980. MIC is an extremely volatile and highly toxic chemical with an IDLH (immediately dangerous to life or health) concentration of approximately 3 ppm.

By 1984 the plant was operating below design capacity following declining Indian pesticide demand. Multiple safety systems had been degraded or shut down to reduce operating costs: the refrigeration unit on the MIC storage tank had been shut off; the gas scrubber was on standby; the flare tower was disabled for maintenance. The plant’s MIC storage Tank 610 held approximately 42 tonnes.

Night of 2-3 December 1984

At approximately 22:30 on 2 December 1984 a plant worker discovered water entering Tank 610 — the precise route remains disputed. The water reacted exothermically with the MIC. Tank temperature rose past 200°C; pressure rose past 40 psi.

The relief valve opened at approximately 00:30 on 3 December 1984. Approximately 27 tonnes of MIC gas vented into the atmosphere over the following 90 minutes. The plant alarm was sounded but the public siren was kept off to “avoid panic.”

The prevailing northwesterly wind carried the cold-dense MIC cloud at ground level across the adjacent shantytowns of Jaiprakash Nagar and Kazi Camp. Sleeping residents woke struggling for breath, their lungs filling with fluid. Many ran towards the apparent open air — directly into the moving cloud.

Death toll

The Indian government’s official immediate death toll (declared 6 December 1984) was 2,259. Subsequent revisions raised the official immediate toll to 3,787. The Madhya Pradesh government’s 2010 affidavit to the Indian Supreme Court documented:

— Immediate deaths: 3,787 — Total deaths from exposure: 15,310 — Permanent total disability: approximately 3,900 — Permanent partial disability: approximately 41,000 — Temporarily injured: approximately 521,000

Independent Indian medical research estimates total deaths from acute and chronic exposure to be 20,000 or more.

What followed

Union Carbide chairman Warren Anderson flew to India on 7 December 1984 and was arrested in Bhopal then released on $2,000 bail. He returned to the United States and never returned to India to face the criminal charges. The Indian Supreme Court declared him an absconder. He died in Florida on 29 September 2014 aged 92 without ever standing trial.

The civil settlement of February 1989 between Union Carbide and the Government of India was $470 million — an average of approximately $500 per acutely affected person. Independent legal analysts have characterized the settlement as inadequate.

Eight Indian Union Carbide officials were convicted of criminal negligence in June 2010 — 26 years after the disaster. They were sentenced to two years each. The plant site has never been fully remediated; groundwater contamination of the surrounding neighbourhoods continues to produce documented birth defects.