1. Accident Overview
December 3, 1984, the capital of Madhya Pradesh, India Union Carbide's pesticide plant in Bhopal methyl isocyanate leak accident, the 4000 residents of poisoning, 200,000 people suffer, is unique in the history of the world's major industrial tragedy.
2. Accident Analysis
(1) U.S. company Union Carbide pesticide plant in Bhopal, India on gas leak (mic) cause of the accident investigation report
Survey showed that the accident was due to 120 to 240 gallons (454.25 - 908.50 liters) of water into the methyl isocyanate (mic) tank caused an exothermic reaction, resulting in increased pressure, explosion-proof membrane rupture caused. Also identified as the tank contains a large number of chloroform (chloroform is the mic for making the initial reaction inhibitor added), chloroform decomposition of chloride ions, so that the tank (made of 304 stainless steel) corrosion, and the formation of free iron ions, iron ions in the catalyst and speed up the reaction. As the exothermic reaction continuing, rapid temperature rise inside the tank, resulting in pressure up to 40 lbs soon / inch 2 (275.79 kPa) or more, explosion-proof membrane rupture, the safety valve open, leak a lot of mic. Leakage of the mic, wherein sodium hydroxide scrubber. Because of the scrubber capacity is too small, not all in and the mic. The last line of defense is the burning towers, but the results also did not play a role in burning tower. Another point is also very important that the existing _set_ of mic tank cooling system, so that mic tank temperature is always maintained at about 0.5 ℃. But the survey shows that the cooling system since June 1984 had stopped functioning. Thus, there is no effective cooling system, can not control the rapidly produce a large number of mic gas. On water access issues has not been thoroughly investigated, may be due to the operator to make the tanks with nitrogen to maintain normal pressure, and nitrogen in the open when the error caused by open water.
(2) India's Bhopal gas accident investigation
Its findings that the Union Carbide gas leak in the prevention of harmful measures there are serious problems.
① 1984 年 12 2 April, for the maintenance and shut down the exhaust pipe outlet is located in the torch device;
② exhaust scrubber and not in time to run through the pipes;
③ lack of accident prevention plan, no training in dealing with emergencies;
④ not alert to the residents;
⑤ Alarm and operation manually, rather than be controlled by computer;
⑥ capacity and emergency safety devices are incompatible with the expected gas flow, there are shortcomings in the design and contradictory;
⑦ refrigeration system was closed only the state can not meet the low-temperature storage conditions, the mic can not be vaporized liquid;
⑧ stored in the tank of potentially dangerous substances related features do not fully understand, and the resulting information is not *;
⑨ not equipped to work correctly on any occasion can be a gas leak early prevention systems.
(3) New York newspaper's findings on the cause of the accident
After seven weeks of the newspaper investigation that the disaster was due to operational errors, design lack of maintenance training, failure and neglect caused. Surveys indicate that at least 10 in violation of the Corporation and India's production rules.
② fuse buried violation of operating rules. According to the survey, there is the following illegal operations:
a.12 May at 23:30 on the 2nd, a worker found started to leak of methyl isocyanate, a foreman that is water leakage, a few minutes before deciding to deal with it, occurred within a few hours after the strong reaction tank.
b. A few months before the accident, the factory power supply tension, in order to solve this problem, Explorer, and Union Carbide Corporation U.S. deliberations (but based company spokesman said, and they did not discuss) is designed to cool off the isocyanate methyl ester to prevent the chemical reaction of the cooling device, which is out of the coolant Freon, used in factories elsewhere. Regulations states: "In order to maintain normal circulation tanks, cooling continuously in 'running' state."
c. 2 hours before the accident, a trained, but do not understand the operating procedures of the factory workers, on instructions from the foreman of a new command, and a flush tank connected, but not completely isolate the tank and pipes, which is prohibited by regulations of.
d.3 main station safety devices (sprinkler ignition, scrubbers), where 1 unit failure in a few days ago, another 2 weeks has been no maintenance.
e. methyl isocyanate Section foreman qureshi on duty, said the plant's equipment is * not live, and for this reason, he began to neglect the warning. In three tanks, including a pressure in the l-hour period increased by 5 times.
l. Bhopal plant is not an advanced computer system to monitor storage tanks, and quickly warned leakage. Factory depends on whether the tears to the eyes of the workers aware of leaks. In addition, this little factory automation equipment in 1983 only to reduce the methyl isocyanate plant of 12 operatives, only 6 people.
8. Did not fire warning devices. Night of the accident, warning, similar to the peacetime training of the sirens, the noise of these 20 times a week.
③ lightly lead to disaster. December 2 evening, workers do not have to understand the system pressure changes. 23, the one on duty in the operating room the old operator sumandey see the tank pressure is 10 lbs / inch 2 (68947.6 Pa), 5 times normal, but did not catch his attention. 23:30, methyl isocyanate Section of workers away from the control room 100 feet (30.5 meters), feel the leak, the eyes began to cry. Operator v. Ⅵ. singh found that 50 feet (15.24 meters) at a droplet, and a yellow gas; 23:45, he went to the control room to tell the foreman qureshi methyl isocyanate leak things, after a while children, qureshi only to find leaks. But to at 0:40 on the 3rd and no one cause and then take steps to investigate leaks. Serious dereliction of duty led to a disaster. Plant usually uses methyl isocyanate analysis behind, there is no measurement of methyl isocyanate in the presence of c1-impact, because a small amount of water containing c1-exist, will result in a high drug activity. Mic should be limited to the tank, leaking storage tanks in the mic's volume of 13,000 gallons (49,210.33 liters), accounting for 87% of tank capacity, more than the maximum allowable working capacity [11,000 gallons (41,639.51 liters), accounting for tanks 73% of the total], even the 11,000 gallons the plant also exceeded the limit prescribed amount (60%). This limitation is mainly because there is a strong reaction in the tank when the pressure rises slowly.
④ reason for the disaster caused by speculation. There are 13,000 gallons in the tank of chemicals, such as response to and need 420 gallons of water (1589.87 liters), the tank can not enter so much water. Therefore, investigators believe there may be other reactions: reaction of water and light gas, water and corrosive phosgene reaction of chloride ions, the reaction of ci-and stainless steel tanks and the release of a large number of hot iron, lead and methyl isocyanate ci-role and emit more heat, coupled with the release of chloride ion metal reaction, resulting in severe reactions can start.
Violent reaction to methyl isocyanate polymerization, the formation of a plastic material, and release a lot of heat, so the tank liquid temperature, methyl isocyanate vapor, and finally the tank wall rupture. At that time, cooling off, not so cool tanks. Investigation team believes that a small amount of water can cause a chain reaction occurred (500g may enter the water). Recipe for disaster, there are other possibilities: not only water and cans of liquid mic response, and the alkali washing tower and the closed system can be poison in the reaction. In addition to the water and alkali, the mic can be volatile and impurities such as acids, iron reaction.
⑤ pollution sources. Union Carbide Corporation and India with nuclear magnetic resonance spectroscopy showed that leakage of the tank at least five kinds of impurities, including water, iron and alkali metal ions. 2 hours before the accident, a worker had a wash tank and connected, but not completely isolated from the tank and pipes, water may flow into the tank at this time; to prevent water loss, with nitrogen instead of air in the tank, there may contain nitrogen in the water. At the same time, workers add lye to the scrubber, the scrubber and the tank is a complex of pipes and valves connected to the normal state of the valve is closed, but sometimes open or cause leakage. Metal ions is mic tank corrosion products.
⑥ ignore worker training. As the plants lack of funds, money managers think important than security, training of workers decreased. Sales occurred in 1982, the deficit has lost many skilled workers. Accident, only 20 operatives familiar with the mic plant. In addition, the quality of workers is too low, mic operator should have a university degree, and here were all high school graduates. |
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