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1-14 The Worst Chemical Plant Tragedy: Bhopal, India, 198413

The Bhopal, India, tragedy occurred on December 3, 1984, in a pesticide plant jointly owned by Union Carbide (USA) and its affiliate Union Carbide India Limited (UCIL). More than 2500 lives were lost due to inhalation and exposure to methyl isocyanate (MIC) vapor released from the plant. Another 200,000 people suffered various levels of exposure, with the adverse effects ranging from blindness to nausea. Many people who survived the incident suffered from severe health effects for the rest of their lives.

MIC was used as an intermediate chemical in pesticide production and was stored on-site. This compound is reactive, toxic, volatile, and flammable. The maximum exposure concentration of MIC for workers over an 8-hour period is 0.02 ppm (parts per million). Individuals exposed to concentrations greater than 21 ppm experience severe irritation of the nose and throat. Death at larger concentrations of MIC vapor is due to respiratory distress.

MIC demonstrates a number of other hazardous physical properties. Its boiling point at atmospheric conditions is 39.1°C, and its vapor pressure is 348 mm Hg at 20°C. The vapor is about twice as heavy as air, meaning that the vapors stay close to the ground once released. In addition, MIC reacts exothermically with water. Although the reaction rate is slow, with inadequate cooling the temperature will increase and the MIC will begin to boil. MIC storage tanks are typically refrigerated to prevent this.

At the time of the MIC release, the Bhopal plant was under extreme financial pressure. It was able to sell only about one-third of its design capacity on the Indian market. In June 1984, the plant’s managers decided to turn off the refrigeration system on the 15,000-gallon liquid MIC storage tank in an effort to reduce costs. A flare system was also present to burn any MIC vapors from the storage tank, but the flare was taken out of service several weeks prior to the incident due to a corroded pipeline. A sodium hydroxide (NaOH) scrubber system was also present to handle small releases, but it had been taken out of service for cost savings. With the shutdown of the refrigeration system, flare, and scrubber, no mitigative safeguards remained between the MIC storage tank and the external environment.

The area around the plant was zoned for industrial use. However, the siting of a major chemical manufacturing plant at the city’s edge created a large opportunity for employment. Several shanty towns were built immediately adjacent to the plant and were inhabited by more than 30,000 people. Zoning laws were in place to prevent the establishment of such shanty towns, but local politicians looked the other way regarding the enforcement of the zoning laws.

The incident was initiated by water contamination of the 15,000-gallon liquid MIC storage tank. Many theories have been proposed to explain how this happened, but there is no publicly available evidence confirming any of these theories. The water caused the MIC to heat up and boil. The pressure in the storage tank increased until the relief system opened, discharging the MIC vapors directly into the air. The temperature of the MIC in the vessel was reported to reach 100°C—well above its boiling point. An estimated 25 tons of toxic MIC vapor was released. The incident occurred during the night when most residents in the adjacent shanty towns were asleep. The toxic cloud dispersed into the shanty town areas, with tragic consequences: The residents of the shanty towns suffered many of the deaths and the severest of injuries during the MIC release.

Prior to the incident, Union Carbide was viewed as a large, well-respected, high-tech American company. In 1980, its annual sales totaled $9 billion. The company had 116,000 employees at 500 sites. It had successfully operated the Oak Ridge National Lab for 40 years—a very important facility for the U.S. nuclear program. Union Carbide produced many well-recognized consumer products, including Eveready batteries, Prestone antifreeze, and Linde gases. Graduating chemical engineers considered Union Carbide a “must interview” company and a very desirable employer.

Before the incident, Union Carbide stock traded for a price between $50 and $58. In early 1985, after the Bhopal incident, the stock price dropped to $32 to $40. Union Carbide also became the target of a hostile takeover by GAF Corporation. To repel this takeover, Union Carbide was forced to sell its consumer products division—its most profitable division. In 1986, the company sold assets worth $3.3 billion to repurchase 38.3 million shares of stock in an effort to protect the company from further takeovers. It was able to retain its commodity chemicals division.

In February 1989, the Supreme Court of India mediated payment of $470 million from Union Carbide and Union Carbide India. Union Carbide paid the settlement within 10 days of the order.

The downward spiral of Union Carbide continued until the remaining assets were purchased by Dow Chemical in 1999. The Bhopal incident was the beginning of the end for Union Carbide.

In March 1985, the AICHE, responding to industry concerns about the Bhopal incident and chemical plant safety, established the Center for Chemical Process Safety. According to the Center, CCPS is “dedicated to improving the ability of engineers to deal with process hazards.” Today, CCPS is a world leader in chemical process safety.

The Bhopal incident also resulted in a considerable number of industry initiatives and government regulations related to process safety. Clearly, incidents have a lasting impact on the reputation of the chemical industry and can change the practice of chemical engineering forever.

Root causes are defined as “failures … that lead to an unsafe act or condition resulting in [an] accident.”14 For any accident, there are typically multiple root causes. If any of those root causes did not occur, then the accident would not have occurred. For the Bhopal incident, the immediate root cause of the incident was the presence of water in the MIC storage tank.Several other root causes occurred, including turning off the refrigeration system, the flare, and the NaOH scrubber system. If a detailed incident report were publicly available, other root causes would likely be identified. Although no official, publicly available, and detailed report of the Bhopal incident was ever published, publicly available information suggests almost all of the 20 elements of RBPS, as shown in Table 1-18, were involved.

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