MIC (Methyl Isocyanate) Gas was leaked on the night of 2-3 December 1984 at the Union Carbide India Limited pesticide plant in Bhopal, Madhya Pradesh, India. It is considered as world’s worst industrial disaster taking lives of at least 3787 (16000 lives are claimed) and non-fatal injuries to atleast 5,58,125.
The Indian government and local activists argue that slack management and deferred maintenance created a situation in which the routine maintenance of pipes caused the water to flow back into a MIC tank and caused the catastrophe. The Union Carbide Corporation (UCC) argues that the tank has been sabotaged by water.
In January 1982, 24 workers who were all admitted to hospital were exposed to a phosgene leak. None of the workers were ordered to wear masks. One month later, in February 1982, 18 workers were affected by a MIC leak. A chemical engineer came into contact with liquid MIC in August 1982, leading to burns in excess of 30% of his body. Later that same year, in October 1982, another MIC leak occurred. The MIC supervisor suffered severe chemical burns in an attempt to stop the leak and two other workers were severely exposed to the gasses. In 1983 and 1984 leaks of MIC, chlorine, monomethylamine, phosgene and sometimes combined carbon tertachloride occurred.
There were three 68,000 liters of liquid MIC storage tanks in the Bhopal UCIL facility: E610, E611 and E619. In the months leading to the leakage in December, liquid MIC production was under way and was used to fill these tanks. The UCC safety regulations specified that no single tank should be filled with liquid MIC in excess of 50% (30 tons here). Each tank has been pressurized with inert gas. This pressure allows liquid MIC to be pumped out of every tank as required and also keeps impurities out of the tanks.
Tank E610 lost its ability to effectively contain most of its nitrogen gas pressure at the end of October 1984. It meant that the MIC liquid in it can not be pumped out. The E610 tank contained 42 tons of liquid MIC at the time of this failure. Shortly after this failure, MIC production at the Bhopal facility was stopped and parts of the plant for maintenance were shut down. Maintenance included shutting down the flare tower of the plant in order to repair the corroded pipe. With the flare tower still out of service, carbaryl production was resumed in late November using MICs still in use in both tanks. An attempt to restore pressure in the E610 tank failed on 1 December, so that the 42 tons of liquid MIC contained in it could not be pumped out. .
In early December 1984, most of the safety systems associated with the MIC failed and many valves and lines were in poor condition. In addition, several vent gas scrubbers and the steam boiler were out of service to clean the pipes. Water was supposed to have entered a side pipe and a tank E610 in the late evening of 2 December 1984 while trying to unclose. The introduction of water into the tank led to a runaway exothermic reaction that was accelerated by contaminants, high ambient temperatures and several other factors, such as the presence of iron from non-stainless steel pipelines. Although initially normal at 10:30 p.m., the pressure in the E610 tank increased by a factor of 5 to 10 psi (34.5 to 69 kPa) by 11 pm. Two senior staff assumed that the reading was a malfunction in the instrumentation. By 11:30 p.m., workers in the MIC region felt the effects of minor MIC gas exposures and began to search for leaks. One was found at 11:45 p.m. and reported on duty at that time to the MIC supervisor. The decision was taken after 12:15 a.m. to tackle the problem Tea breaks and employees have been instructed to continue looking for leaks in the meantime. During the break, MIC area employees discussed the incident. [
In the five minutes following the tea break at 12:40, the reaction in the E610 tank reached a critical state at an alarming rate. Temperatures in the tank were off-scale, exceeding 25 ° C (77 ° F) and tank pressure was shown at 40 psi (275,8 kPa). One employee saw a concrete slab above the E610 crack when the emergency relief valve burst open and the pressure in the tank continued to increase to 55 psi (379.2 kPa) even after the atmospheric ventilation of toxic MIC gas had started. At least three safety devices that were malfunctioning, not in use, insufficiently sized or otherwise rendered inoperable should have prevented or at least partially mitigated direct atmospheric ventilation:
A cooling system was designed to cool liquid MIC tanks, shut down in January 1982 and removed from Freon in June 1984. Since refrigeration was assumed by the MIC storage system, its high temperature alarm has long been disconnected at 11 ° C (52 ° F) and storage temperatures ranged from 15 ° C (59 ° F) to 40 ° C (104 ° F).
A flare tower to burn the MIC gas that had been removed for maintenance by a connecting pipe and was improperly sized to neutralize the leakage of the size produced by the E610 tank.
A vent gas scrubber, deactivated at the time and in’ standby’ mode, had similarly insufficient caustic soda and power to safely stop the leak of the magnitude.
Some 30 metric tons of MIC escaped in 45 to 60 minutes from the tank into the atmosphere. This would increase to 40 metric tons in two hours.] The gasses were blown over Bhopal in a southeast direction.
At 12:50 a.m., an UCIL employee activated the alarm system of the plant. It became difficult to tolerate the concentration of gas in and around the plant. The system activation triggered two siren alarms: one that sounded in the UCIL plant and the other to the public and to the city of Bhopal. The two siren systems were decoupled from each other in 1982, so that the factory warning siren could be left on when the public was turned off, and that’s exactly what was done: the public siren sounded briefly at 12:50 a.m. And was swiftly turned off, as the company procedure meant to avoid alarming the public about tiny leaks around the factory. Meanwhile, workers evacuated the UCIL plant, traveling upwind. The health system became overloaded immediately. Almost 70 percent of underqualified doctors were in the severely affected areas. For thousands of casualties, medical staff were unprepared. Doctors and hospitals were not aware of the correct MIC gas inhalation treatment methods.
Control Measures that could be taken are as follows:
- Proper and extensive maintenance planning should be done keeping in mind the effect of a defective system in on the hazard that it can cause.
- Rules and protocols should be made which gives proper guidance case of leakage and the immediate action that should be taken (in this case the worker took the situation lightly and thought of looking into the leak case after as tea break).
- The production of the gas should not be started when any important part is still under maintenance (in this case the flare tower was out of order due to maintenance work and still the resumed the production).
- Working in such a hazardous atmosphere worker should be given proper safety equipment’s and safety training.
- in-depth Study of previous leaks should be done to know the main cause of the leak (the frequent leaks happened in 1982 and 1983 clearly showed that something was seriously wrong with the plant).
- Safety standards should be strictly followed (it was mentioned that only 50% (30 tons) of the storage tank should be filled but it was 42 tons).
- Safety devices should be always in a working condition (none of the 3 safety device were in working condition at the time of leaks).
- Reading of the instruments should never be neglected and safety checks should be done immediately in case of danger ( Two different senior refinery employees assumed the pressure reading was instrumentation malfunction ).
- Making changes to a system should be properly conveyed to other departments so that they can adjust to the new settings (the refrigeration system used to cool down MIC tank was shut down in 1982 and temperature gauge were disconnected since then).
- Proper alarming system should be there to inform people of leaks (in this case to avoid inconveniences to people from alarm from small leakage they made change to alarm system so it would switch off after a while, if they would had informed people on time many lives would have been saved).
- No production plants should be given permission to set-up a plant near a residential area.
- The hospitals near the plants should be made aware of the situations that can arise and steps to handle those situations.
- Proper medication should be made available in advance to the hospital near plant to save people in worst case scenarios.
people interested to know more about this disaster can watch a documentary made on this incidence, link is given below: