1969 - Union Carbide India Limited (UCIL) commissions a chemical plant at Bhopal, the capital of the state of Madhya Pradesh, in the centre of India. The plant initially formulates pesticides from concentrates imported from the US.
UCIL is 60% owned by the United States-based Union Carbide Corporation (UCC), one of the largest chemical companies in the world.
1980 - The Bhopal chemical plant is upgraded to allow the production of chemical precursors on-site. The plant will produce methyl isocyanate (MIC) then react it with another chemical to form Sevin, an agricultural pesticide.
The MIC produced at the Bhopal plant will be stored in bulk in two underground, 57,000 litre tanks, named tank 610 and tank 611. A third tank, 619, is to act as a backup. On the night of the disaster, tank 610 contains 41 tonnes of MIC.
According to UCC's 'Reactive and Hazardous Chemicals Manual', "methyl isocyanate is a recognised poison by inhalation and is intensely irritating to breathe. It causes severe bronchospasm and asthma-like breathing. Major residual injury is likely in spite of prompt treatment."
The chemical reacts violently with water.
1981 - At the end of December a phosgene leak at the plant injures three workers, one of who dies the next day.
1982 - Twenty four workers at the plant are overcome by a second phosgene leak in January. A MIC leak affects 18 people in February. In May a three-man safety audit team from UCC headquarters in the US finds "a total of 61 hazards, 30 of them major and 11 of them in the dangerous phosgene/methyl isocyanate units," at the Bhopal plant.
In August a chemical engineer at Bhopal receives burns to over 30% of his body after coming into contact with liquid MIC. In October a combined MIC, hydrochloric acid and chloroform leak injures three workers in the plant and affects a number of residents in the surrounding neighbourhoods.
1983 - The pressure indicator control, temperature indicator and the level indicator for the MIC storage tanks begin to malfunction. They are still malfunctioning on 2 December 1984.
1984 - In June the refrigeration unit used to cool the MIC tanks is shut down as a cost-cutting measure.
Staff cutbacks further affect the MIC facility. The production crew is cut by half from 12 to six workers. The maintenance crew is reduced from six to two workers. In the control room, one operator monitors about 70 panels, indicators and controllers. The period of safety training for workers in the MIC unit is brought down from six months to 15 days.
The vent gas scrubber connected to tank 610 at the Bhopal plant begins to malfunction in October. The caustic flow indicator on the scrubber is also malfunctioning, making it difficult to verify whether the unit is operating or not.
The flare tower goes out of service when a section of corroded pipe leading to it is removed. On the night of the disaster the pipe has still not been replaced.
The MIC production unit is temporarily shut down in the middle of October because a large amount of the chemical is already in storage in tanks 610 and 611.
The position of second shift maintenance supervisor for the MIC unit is abolished on 26 November.
Six days later the series of failures turns catastrophic.
In the hours before midnight on 2 December, water enters MIC storage tank 610. A runaway reaction occurs that releases tonnes of toxic, white, MIC gas.
Attempts to control the leak fail due to either the breakdown of safety systems or because the systems are overwhelmed by the amount of the gas released. Tank 610 cannot be cooled and the reaction cannot be slowed because the tank's refrigeration system has been taken out of commission as a cost-cutting measure.
The gas is not diverted to a neighbouring tank because a faulty pressure gauge indicates the tank is full when it is really empty.
The gas scrubber connected to the tank is ineffective because it is either faulty or overwhelmed by the volume of gas.
The gas cannot be burnt off through a flare tower because the supply pipe to the tower has been removed and not replaced.
It is now too late and the reaction is too intense to dampen the gas with water.
The gas vents directly to the atmosphere and begins to settle over the surrounding shanty towns and neighbourhoods. The gas eventually covers an area of about 20 square kilometres.
UCIL informs the authorities of the leak at 2:00am. The siren at the plant used to warn the public of an accident is sounded at about the same time. Police are not informed about the type of gas involved until 3:00am.
Residents have no idea of the best response to the disaster. Instead of remaining indoors they attempt to flee through the toxic fog.
At least 500,000 people are directly exposed to the gas. About 2,500 are killed immediately. The gas causes their lungs to ulcerate and swell with fluid. Thousands more die within the coming days and more than 200,000 are injured.
In the immediate aftermath of the leak, Bhopal hospitals treat at least 130,000 patients exposed to the gas. Over 44,000 victims are treated elsewhere in the state.
According to a report on the disaster published by the Government of Madhya Pradesh in December 1986, "Within hours all the hospitals of Bhopal were full of poison gas-stricken victims. Doctors, medical students and volunteers worked round the clock but in the absence of any open toxicological information about MIC, only symptomatic treatment could be provided. ... A trail of both short-term and long-term problems ensued. ... No one knew for certain what gases had been released from the Union Carbide facility. ... The Union Carbide management was completely silent on this and did not even say what toxic gases had been released from their facility or what antidotes could help."
Figures for the numbers killed or injured by the toxic gas rise over the years.
In February 1989 the Indian Government estimates that 3,000 died. A further 30,000 sustained permanent or total disabilities. About 20,000 received temporary or partial disabilities. Around 2,000 were affected by serious injuries. Another 50,000 sustained minor injuries.
In 1990 the Madhya Pradesh State Government finds that 3,828 died as a direct result of the disaster and that several thousand others experienced permanent or partial disabilities.
By 1 December 1999 the Office of the Indian Medical Commissioner had registered 22,149 fatalities directly attributable to the disaster.
In 2003 the annual report of the Madhya Pradesh Gas Relief and Rehabilitation Department lists 15,248 people as having died as a result of the gas leak. A further 554,895 had sustained varying degrees of injuries or disability.
Twenty years after the incident Amnesty International reports that "more than 7,000 people died within days. A further 15,000 died in the following years. Around 100,000 people are suffering chronic and debilitating illnesses for which treatment is largely ineffective."
The illnesses caused by the gas leak include eye disease, respiratory disorders, immune system impairment, neuromuscular disorders, neurological disorders, gynaecological disorders, miscarriages, mental health problems, and cancer.
Immediately following the disaster the plant site is declared a crime scene, sealed and placed under the control of the Indian Central Bureau of Investigation.
UCC Chairman and Chief Executive Officer Warren M. Anderson travels from the US to India on 4 December. He is placed under house arrest in Bhopal on 7 December. Anderson is released on bail of US$2,000 the same day and advised by the Indian Government to leave the country within 24 hours. He flees. Anderson never returns to India. In 1986 he retires from UCC.
Anderson and eight senior officials from UCC's Indian subsidiary are later charged in India with "culpable homicide amounting to murder". In 1996 the charge is downgraded to "culpable homicide not amounting to murder" and "death by negligence".
Work is allowed to continue in the plant in order to process the remaining MIC on site into pesticides. The processing is completed by the end of December. The plant is closed in April 1985.
1985 - The Indian Government passes the Bhopal Gas Leak Disaster Act in March. The Act gives the government the exclusive right to represent and act on behalf of victims in any civil litigation in India or elsewhere. It also prevents victims from pursuing individual court claims against UCC for damages or personal injury due to the gas leak.
1986 - On 5 September the Indian Government files a US$3.3 billion compensation claim against UCC on behalf of all the Bhopal victims.
1987 - On 1 December India's Central Bureau of Investigation files homicide charges against Warren Anderson.
1988 - India formally charges UCC with criminal wrongdoing in May. An arrest warrant for Anderson is issued by the Bhopal District Court in November.
1989 - In February the Indian Government accepts a Supreme Court-ordered settlement of US$470 million on the compensation claim. UCC contributes $420 million to the payment. The balance is paid by UCIL.
Under the terms of the settlement, the payment ends all of UCC's civil liabilities for the disaster. However, the settlement does not apply to liabilities arising from ongoing land and water pollution at the plant site.
The Supreme Court also orders that all criminal proceedings related to the gas release be dropped and that the accused be deemed acquitted.
Although a settlement has been reached, the Indian Government is slow to pass on the compensation funds to the victims of the disaster. When the compensation is finally distributed in 2005 most of the 572,173 victims receive about US$1,280 each.
1990 - Activist groups petition the Indian Supreme Court to overturn the settlement agreement. On 12 January the India Government announces it will support the petitions. The government repudiates the original settlement as inadequate and announces that it has returned to the original US$3 billion compensation claim and will attempt to pursue criminal charges against UCC executives.
1991 - In October the Supreme Court rejects the petitions to overturn the settlement agreement and closes legal proceedings in relation to civil liabilities. However, the court lifts the immunity on criminal prosecutions related to the disaster, opening the way for criminal charges to be laid.
1992 - The criminal case against Warren Anderson and eight senior officials from UCC's Indian subsidiary is reopened by a court in Bhopal. All the accused refuse to appear before the Indian courts.
Proclamations directing Anderson to face trial in the Bhopal court are published in 'The Washington Post' in January.
On 1 February Anderson and his co-accused are declared "fugitives from justice" by the chief judicial magistrate of Bhopal. The chief judicial magistrate issues a non-bailable arrest warrant against Anderson in March. The court also orders the Indian Government to seek the extradition of Anderson from the US.
1996 - Tests by the Madhya Pradesh Public Health Engineering Department's State Research Laboratory of ground water from 10 tubewells near the Bhopal site find that the water "is contaminated with bacteria and there is a heavy presence of chemicals".
"The tubewells in these areas were tested five years back and at that time too the results showed chemical contamination," a confidential report by the laboratory states. "Hence, it is established that this pollution is due to chemicals used in the Union Carbide factory that have proven to be extremely harmful for health. Therefore the use of this water for drinking must be stopped immediately."
Union Carbide denies there is any contamination of groundwater around the plant, citing studies by the National Engineering Environmental Research Institute (NEERI).
1997 - The Bhopal Municipal Corporation declares that 250 wells in the vicinity of the plant are "unfit for drinking".
1999 - In November the environmental group Greenpeace International releases a technical analysis of the toxic contaminants at the Bhopal site. The analysis finds "substantial and, in some locations, severe contamination of land and drinking water supplies with heavy metals and persistent organic contaminants both within and surrounding the former UCIL pesticide formulation plant".
"Though less acute than the exposure which took place as a result of the 1984 MIC release, long-term chronic exposure to mixtures of toxic synthetic chemicals and heavy metals is also likely to have serious consequences for the health and survival of the local population. This open, but largely undocumented, contamination must be urgently and effectively addressed such that the communities of Bhopal are no longer exposed to this legacy of pollution."
On 15 November a class action against UCC and Warren Anderson is filed in the Federal Southern District Court of New York. The suit charges UCC and Anderson with grave violations of international law and human rights arising from their "unlawful, reckless and depraved indifference to human life" in perpetrating the disaster. The action is dismissed by the court on 28 August 2000.
2001 - A court of appeal rules that claims relating to contamination of ground water and soil in and around the Bhopal plant and consequent health damages can be returned to the Federal Southern District Court for reconsideration.
2002 - On 28 August an application to reduce the criminal charges against Anderson is rejected by the Indian courts.
In November the Federal Southern District Court of New York forces UCC to release internal documents relating to the Bhopal disaster.
Documents from 1989, 1990 and 1995 show that UCC knew by 1989 that Indian analyses claiming there was no chemical contamination at the abandoned plant, including those by NEERI, were suspect and that there might be contamination.
In August Anderson is discovered living in New York State.
2003 - In March the Southern District Court of New York again dismisses a civil damages lawsuit brought by Bhopal survivors, this time on the grounds of limitation. The survivors appeal.
The Indian Government serves the US Government with extradition papers for Anderson on 1 July.
2004 - On 17 March a US Appeals Court rules that a request for "remediation" to restore the environmental quality of the Bhopal site brought by plaintiffs from Bhopal against UCC could not be barred by the statute of limitations.
The Appeals Court declares that the Southern District Court should be free to revisit its dismissal of the claim for plant site "remediation" if the governments of India or Madhya Pradesh sought such action.
Subsequently, the governments of India and Madhya Pradesh urge the Southern District Court to order UCC to pay for the clean-up of the plant site and pollution damage.
2006 - In April, following a hunger strike by Bhopal survivors, Indian Prime Minister Manmohan Singh agrees to clean up the Bhopal site, provide fresh drinking water for local people and construct a US$23 million memorial to the victims of the disaster.
2010 - The trial of seven living senior officials from UCC's Indian subsidiary finally comes to an end on on 7 June. All seven are found guilty of "death by negligence" and "culpable homicide not amounting to murder" for their role in the Bhopal incident. They face sentences of up to two years in prison and fines of more than US$2,200 each. UCC's Indian subsidiary is also found guilty of the same charge and fined US$11,000. The seven former officials, all of who are Indian, are granted bail pending an appeal.
2014 - Warren Anderson dies in a Florida nursing home on 29 September. At the time of his death, the criminal prosecutions against him and Union Carbide are still open and pending in the Indian courts. All the accused remained identified as "absconders" by the Bhopal District Court and the Supreme Court of India.
Present day - More than 20,000 people continue to live in close proximity to the abandoned plant at Bhopal. Hundreds of tonnes of chemical residues and waste materials remain on the site, including Sevin, Sevin tar residue, naphthol tar residue, and hexachlorocyclohexane solids.
What caused the gas leak at the Bhopal chemical plant?
Union Carbide claims the disaster was the result of a deliberate act of industrial sabotage by a disgruntled employee. According to Union Carbide, during a shift change beginning at 10:45pm on 2 December an unnamed employee connected a water hose directly to tank 610 through a fitting for the tank's local pressure gauge. Union Carbide also alleges that following the disaster, staff at the plant deliberately covered up the sabotage and falsified records.
Union Carbide has never released the name of the alleged saboteur but says it knows who the person is and has passed the information to the Indian Government.
Other observers attribute the disaster to poor management, cost cutting and lax safety and plant maintenance routines.
A report by the International Confederation of Free Trade Unions and the International Federation of Chemical, Energy, and General Workers Unions concludes that "the disaster was caused by insufficient attention to safety in the process design, dangerous operating procedures, lack of proper maintenance, faulty equipment, and deep cuts in manning levels, crew sizes, worker training and skilled supervision".
"The operating and maintenance errors which led to the MIC release were made by management of the Bhopal plant and Union Carbide India Limited (UCIL)," the report says.
"However, responsibility for the disaster also rests with UCIL's parent multinational, the US-based Union Carbide Corporation (UCC). UCC insisted on a process design requiring large MIC storage tanks. ... In addition a 1982 corporate inspection report demonstrates that UCC knew the Bhopal plant had major safety problems. But the company did not take sufficient action to correct them. ...
"The Bhopal disaster was caused by a combination of factors, including the long term storage of MIC in the plant, the potentially undersized vent gas scrubber, the shut-down of the MIC refrigeration units, the use of the backup tank to store contaminated MIC, the company's failure to repair the flare tower, leaking valves, broken gauges, and cuts in manning levels, crew sizes, workers training, and skilled supervision. The accident might have been prevented if UCC had done more to follow up its 1982 safety inspection, or if UCIL or the government had heeded the complaints of unions representing Bhopal workers. The effects of the accident were exacerbated by the company's failure to provide adequate information to its subsidiary, authorities and community residents, the siting of the plant close to residential areas, and UCIL's lack of disaster planning."
- International Campaign for Justice in Bhopal
- Bhopal Gas Tragedy Information - Union Carbide Corporation
- Bhopal Gas Tragedy Relief and Rehabilitation - Government of Madhya Pradesh
- A Cloud Over Bhopal: Causes, Consequences and Constructive Solutions - Alfred de Grazia
- BBC NEWS | Programs | Bhopal
- Chronology of the Union Carbide Corporation
- Clouds of Injustice: Bhopal Disaster 20 Years On - Amnesty International
- The Inside Story: 18th Anniversary of Bhopal Disaster - Chemical Industry Archives
- Bhopal: 25 Years of Poison - The Guardian
- Bhopal 30 years on: The women of India are battling the poisonous legacy of the world's worst industrial accident - The Independent