pressure is high at 54 kPa at 20°C, its boiling point is 39°C, and the vapor density is greater than that of air, meaning that the liquid volatilizes readily and the vapor will stay near ground level. When stored, the liquid is kept between –10°C and 0°C in order to maintain a low vapor pressure and to prevent exothermic self-polymerization.
THE BHOPAL DISASTER
On the night of the incident, December 2, 1984, at 11:00 p.m. local time, while many of the Bhopal residents were asleep, it was reported that a plant operator noticed a small MIC gas leak and increased gas pressure inside a storage tank. This leak and pressure were due to water that had entered the storage vessel. At the time, critical refrigeration for the storage system had been moved to another area in the plant, and without refrigeration to slow the reaction of MIC with water, the temperature and pressure rapidly rose within the storage vessel. As the temperature rose, the MIC began to self-polymerize, adding to the heat and pressure. The vapor was first routed to a scrubber for the vent gas that should have neutralized at least some portion of the vapor, but this unit was not active.1 The vapor should then have passed to a flare tower to be destroyed, but the tower was out of service for maintenance because of pipe corrosion. Shortly after midnight, a safety valve opened, sending a MIC gas plume into the air (Broughton, 2005). An emergency water curtain intended to react with the MIC in case of such a release was not designed to manage a release of that scale and was also suffering from corrosion, which likely reduced its efficacy.
More than 40 tons of MIC was released into the impoverished community that surrounded the facility. As the plume traveled through the area, the severe acute irritant effects caused residents living nearby to become disoriented and anxious. In their attempt to escape from the chemical, residents ran out of their homes directly into the gas cloud, which resulted in increased exposure to the chemical. Reportedly, close to 3,800 residents were killed immediately. Thousands more, with estimates of up to 100,000-200,000 people in and surrounding that community, have experienced significant morbidity and mortality, including being partially or totally disabled, and experiencing premature death (Andersson et al., 1990; Beckett, 1998; Hood, 2004; Broughton, 2005; Mishra et al., 2009).
From reports on the event, it is clear that the Bhopal facility was operating with reduced safety standards and equipment. Specifically, the unavailability of the refrigeration, scrubber, flare tower, and water curtain, led Broughton (2005) to conclude that the Bhopal facility operated with “safety equipment and proce-
1 The caustic in the scrubber was warm the next morning, indicating that some of the MIC could have actually reacted with the system despite being offline, but it was not sufficient to control the release.