Bhopal Report
Methyl Isocyanate: The Chemistry of a Hazard Combination of reactivity, toxicity, and volatility makes MIC a tough chemical to handle and places great demands on operational, maintenance, and safety practices Ward Worthy, C&EN Chicago
"Methyl isocyanate (MIC) is reac tive, toxic, volatile, and flammable." So begins the first page of a Union Carbide pamphlet on MIC. It's a good nutshell description of MIC's character. And, although there was no fire at Bhopal, that terse summa ry of properties helps explain how such a disaster could have occurred. Isocyanates (R—N = C = 0 ) are, in general, reactive. They resemble aldehydes and ketones in their pro pensity to undergo addition reac tions with a variety of compounds containing active hydrogen atoms. However, they, like the related isothiocyanates (R—N = C = S) and the analogous ketenes ( R 2 C = C = 0 ) , are also examples of "cumulated un saturated systems," with a = C = Ο (or = C = S) group at the end of the molecule. The cumulative effect of the adjacent double bonds adds to the instability of the molecule, so that isocyanate addition reactions tend to be considerably more vigor ous than similar reactions involv ing aldehydes or ketones. Although that reactivity makes the isocyanates tricky to deal with, it also makes several of them useful as chemical intermediates. Three iso cyanates are of major commercial importance. One is methyl isocya nate (MIC), almost all of which is used to make carbamate pesticides. The other two are toluene diisocyanate (TDI) and 4,4 / -diphenylmeth-
Ihopal
ane diisocyanate (MDI), both of which are used almost exclusively to make urethane and isocyanurate polymers. Small amounts of MIC and other alkyl monoisocyanates are used for other purposes; for exam ple, in the manufacture of certain pharmaceuticals. TDI and MDI, like MIC, are flam mable as well as reactive. And all three are toxic, as indicated by the very low maximum allowable con centrations prescribed for employ ee exposure by the Occupational Safety & Health Administration. These exposure limits, averaged over an eight-hour period, are 0.02 ppm for MDI and MIC, and only 0.005 ppm for TDI. All three chemicals must be treated with great respect. But MDI and TDI are essentially nonvolatile. MIC,
in contrast, is highly volatile. It boils at 39.1 °C (at 760 mm Hg) and it has a vapor pressure of 348 mm Hg at 20 °C. Furthermore, although the liquid is a little lighter than water, the vapor is about twice as heavy as air. If released, it tends to stay close to the ground as it diffuses from the source. Thus, MIC has a much greater potential for damage than do TDI and MDI. That potential became the reality at Bhopal. Union Carbide declines to speculate publicly on what hap pened there, pending completion of its own investigations. However, a brief look at the chemistry of MIC will suggest some of the things that could have happened. As noted, MIC will react with many compounds. The reactions tend to be exothermic and vigor ous. But from a practical standpoint, only a limited number of those re actions conceivably could have tak. en place at Bhopal, given which reactants likely were present. Water is one of the possible reac tants. MIC and water will react to yield methylamine and carbon di oxide. The methylamine reacts fur ther with MIC or other reaction products to give either 1,3-dimethylurea (with excess water) or 1,3,5trimethylbiuret (with excess MIC). A trace of acid or base will promote the reaction. At room temperature, the MICwater reaction starts off slowly. But the reaction produces heat. SpecifiFebruary 11, 1985 C&EN
27
Bhopal Report Methyl isocyanatewill react with many "active hydrogen" compounds...
CH3N=C=0
+
ROH
Ο I! ROCNHCH3
•
An N-methyI carbamate
...with water... CH3N=C = 0
+
ο
H 2 0 (excess)
CH 3 N=C = Ο (excess)
+
H20
•
ii CH3NHCNHCH3 1,3-Dimethylurea
+
C02
CH^ Ο II *- CH 3 NHC-N — CNHCH3 + C 0 2
ί î
1,3,5-Trimethylbiuret
...and with itself
Ο Catalysi
3CH3N = C = 0
11
CH 3
"N
O'
3
'*0
II CH CH,3 Trimethyl isocyanurate
cally, it produces about 585 Btu per lb of MIC, or about 3700 Btu per lb of water. If sufficient quantities of both reactants are present, and if the heat is not somehow removed, the temperature will go up and the reaction rate will rapidly increase to the point that the MIC will start to boil violently. In a closed tank, the pressure could build up to the point that relief valves would open, venting both MIC vapor and car bon dioxide. If safety devices failed to operate, or if they were over whelmed by the amount of vapors being generated, the heavy, nox ious MIC vapors would escape to the atmosphere. It hasn't been established that that's what happened to the MIC storage tank at Bhopal. It doesn't even seem very likely that a large amount of water could suddenly get into the underground tank. Accord ing to a Nezv York Times account (not confirmed by Carbide), tests of the contents of the Bhopal tank haven't shown the presence of the urea and/or biuret that would have been formed by hydrolysis. So the hydrolysis hypothesis, although it can't be discounted altogether, isn't the likeliest one. Another hypothesis, perhaps more plausible, is that MIC, in addition to reacting with a great many other 28
February 11, 1985 C&EN
chemicals, can also react with itself. In the presence of a catalyst, puri fied MIC will form either a cyclic trimer (trimethyl isocyanurate) or a gummy, resinous polymer. (Extreme ly pure MIC will spontaneously form a linear polymer, Carbide notes; however, that doesn't hap pen with the commercial material.) As might be expected, these reac tions are exothermic. Trimerization, for example, liberates about 540 Btu per lb of MIC, equivalent to 54 kcal per mole of trimer. Any of a num ber of substances can catalyze the reactions: strong bases such as sodi um hydroxide or sodium methoxide, triphenylarsine, triethylphosphine, metallic chlorides, and oth ers. However, the reaction rates and the induction periods vary widely with different catalysts. According to the literature, the time required for complete trimerization, using various catalysts, can range from 10 minutes (sodium methoxide) through one hour (ferric chloride) to four weeks (4-dimethylaminopyridine). The point is that runaway reac tions, leading to end results similar to those described above, can take place with MIC even in the absence of massive contamination by water or other reactive substance. Just a trace of catalyst is enough to ini tiate oligomerization or polymeriza
tion. It's not hard to imagine situa tions in which such trace contami nation could occur, despite best efforts at prevention. For that matter, the two hypothe ses can be combined: A small amount of water seeping into an MIC stor age tank might not in itself be suf ficient to support a catastrophic hy drolysis reaction. However, that small amount of water might be con taminated by substances—rust and salt, for example—that sooner or lat er could catalyze an autoreaction. Carbide was well aware of the chemical's hazardous nature. The company prescribes detailed proce dures for its handling, shipping, storage, and use. The rules, not sur prisingly, are aimed at preventing MIC from escaping, from being overheated, or from being contami nated. Containers and other equip ment must be made of stainless steel or glass-lined materials (no pinholes allowed in the lining); other metals are proscribed. Containers must be oversized to allow for expansion. Transfer hoses must be made of flex ible stainless steel or of other suit ably strong material lined with fluorocarbon resins. In transfer operations, and other wise as appropriate, personnel are to be equipped with full protective gear and fresh-air breathing equip ment. Decontamination procedures are specified, and decontaminating materials, including water, activat ed carbon, and sodium hydroxide, are required to be on hand for spill cleanup. MIC must be protected by a "blan ket" of dry nitrogen (dew point —40 °C or below) while in storage, dur ing transfer operations, or whenev er there's a possibility of exposure to air. Although drums may be stored at ambient temperatures (but not in direct sun), MIC in bulk stor age is to be cooled, preferably to about 0 °C. And insulated stainless steel tank cars are specified for rail shipment. The MIC is loaded at 0 °C and shipped under nitrogen at 10 psig. Carbide notes that contamination of MIC is more likely to occur in bulk storage than in tightly sealed drums, and that the potential for loss is greater. Although storage at low temperatures doesn't eliminate
Underground storage installations in Institute storage system include safety monitoring equipment
>>Scrubber/flare
Nitrogen
• Coolant out Circulation
Normal vent
Cooler
-Coolant in From unit storage
Performance (monitor)— • T o auxiliary tank
Temperatur ImonttorJ Ground level
feature nonrtor'
ι Pressure relief device
^TanlcN nventor monitor
^ To process/ w distribution
Sycle pump
Performance "TmonltorJ Feed pump
Normal vent
Nitrogen Prêteur» iwie device
Nitrogen -
Emergency vent
Pressure relief device
Unit product WC unrt tan*»
Storage tanks (3)
Sevin Methyl carbamates
Scrubber
Normal vent
Nitrogen-
Nitrogen
Normal vent pfeeoure nwet device
vent
Flare
Pretstif» | Emergency
Emergency
I
Methomyl unit tank
the possibility of violent reactions, it does slow things down, and thus provides more time for detection and corrective actions. Regarding storage stability, Car bide in its MIC pamphlet specifi cally cautions that "iron, copper, tin, and zinc must be excluded from contact with methyl isocyanate. They catalyze a dangerously rapid trimerization. The induction period varies from several hours to several days. The heat evolved can gener ate a reaction of explosive violence." There are several other references to the dangers of trace contamina tion. For example: "When blanket ing or transferring methyl isocya nate [with nitrogen], use a filter to
1 device
Scrubbers
Flare
Distribution tanks (2)
prevent possible entry of iron rust from the nitrogen supply line"; and "Install check valves or other de vices to prevent backflow of other materials into the methyl isocya nate system. Guard against unex pected pressure surges or failures of the methyl isocyanate feed unit that might push catalytic material back into the methyl isocyanate stor age system." Carbide is obviously serious about this particular subject. According to Carbide, the three u n d e r g r o u n d MIC storage tanks at its Institute, W.Va., plant are equipped with a full array of moni tors, alarms, pressure relief valves, and such, as well as cooling sys tems, a caustic soda scrubber to neu
|
vent
Scrubber
tralize escaped liquid MIC, and a flare to burn escaped MIC vapor. Despite all precautions, things still go wrong. A recent Environmental Protection Agency report—based on inspections of Carbide's own rec ords—documents 28 MIC leaks at the Institute plant from 1980 through 1984. Apparently, control measures were prompt and sufficient. There was no evidence of serious injury from the leaks. Whether MIC es caped the confines of the plant hasn't been determined. A Carbide safety team conducted a routine safety and health survey of the Institute "MIC II Unit" in July 1984. The survey uncovered "no concerns of an imminent naFebruary 11, 1985 C&EN 29
Bhopal Report
Carbaryl can be made with or without methyl isocyanate Methyl isocyanate route CH3NH2 + COCI2 Methylamine
- • CH3N=C=0 + 2HCI
Phosgene
Methyl isocyanate
OH
Ο O-CNHCH,
CH 3 N=C=0 + α -Naphthol
Nonmethyl isocyanate route
1 -Naphthyl-W-methylcarbamate (carbaryi)
Ο II
OH
O-C-CI COCL
HCI α-Naphthol chloroformate
Ο II
O-C-CI + CH3NH2
ture." However, the team did iden tify two "major" concerns: "the pos sibility of a runaway reaction in the MIC unit storage tanks" and a "po tential for serious chloroform over exposure." Team members were more con cerned about runaway reactions in the unit storage tanks than in the underground field storage tanks. In termittent operation of the MIC II unit could result in the unit storage tanks' being used for long-term stor age. "One consequence of this is that the tanks tend to get less atten tion and be sampled less frequently than they do while being used ex clusively as make tanks, with the resulting higher probability of a con tamination going undetected for a relatively long period of time," the report notes. Commenting on the use of brine to cool MIC in the unit tanks, rath er than the chloroform used in the field storage area, the team pointed out that "this provides a source of water contamination and perhaps a potential reaction catalyst (potassi um dichromate or brine system con taminants)." Also, pressures in the unit tanks were such that catalytic materials conceivably could be drawn into the tanks from the flare system. 30
February 11, 1985 C&LM
Ο O-CNHCH, +
HCI
There had been several past in stances of water contamination of the unit tanks. Those instances apparently caused no serious prob lems. This, the team warned, "may have created a degree of overconfidence or lack of concern that could allow a situation to proceed to the point where it is not controllable." Carbide says that the survey team's findings represented a worst-case scenario based on the occurrence of a particular chain of events, and that steps were taken to break the chain. The company adds that the findings weren't applicable to Bho pal, because the Bhopal plant used a fluorocarbon refrigerant rather than brine to cool the MIC. Chloroform monitoring was spot ty at the MIC unit, the report notes, and actual workplace concentrations w e r e n ' t k n o w n . Accordingly, it called for a monitoring strategy to determine worst-case concentrations and to provide a basis for a pro gram to keep chloroform levels be low prescribed safe levels. According to Carbide, the MIC plant at Bhopal, although only about a tenth the size of the one at Insti tute, was built to meet the same safety standards. That assertion has been challenged by, among others,
some Indian government officials, who suggest that the Bhopal plant was built and operated to maximize profits rather than safety, that it was just another shoddy exploita tion of developing countries' hun ger for jobs. Certainly, there were differences in the details of construction. For example, whereas many compo nents, including safety devices, are activated automatically at the Insti tute MIC plant, their counterparts at Bhopal are, in some instances, manually controlled. Carbide points out that although it specified the design standards for the Bhopal plant, the actual design and con struction were carried out by the Indian subsidiary, using locally pro cured e q u i p m e n t a n d materials wherever possible. There were po litical considerations, the company notes. The Indian government did favor a labor-intensive approach— thus the preference for manual rath er than automatic controls. But Car bide emphatically denies that there was any "double standard" where safety was concerned. A detailed safety audit of the plant, made by Carbide in 1982, un covered a number of deficiencies, major and minor, that required cor rective action. But, as in the later Institute survey, n o n e of t h e m threatened imminent danger, and none involved the MIC storage unit. There was a general observation about "problems created by high personnel turnover at the plant, par ticularly in operations." Subsequently, the Indian subsid iary sent its U.S. parent a series of reports outlining progress toward correcting the deficiencies noted in the audit. A final report in June 1984 indicated that all but one of the recommended corrective actions had been taken, and that that one was scheduled for completion in
July. Exercises like the Bhopal audit and the Institute survey either dem onstrate Carbide's concern for safe ty or they demonstrate Carbide's lack of concern for safety, depending on one's prejudices. Prescribing safe ty procedures is one thing, and seeing that they're followed is an other. Recent accounts from India indicate that o p e r a t i o n s at t h e
Operating problems cited at Bhopal MIC plant The actual scenario of what went wrong at the Bhopal plant just after midnight on the morning of Dec. 3 will have to await official reports of investigations. But meanwhile, members of the Delhi Science Forum, a public interest sci ence group in New Delhi, have pieced together information from workers man ning the plant or engaged in repair work. Their report raises many ques tions, but it also points up some of the possibilities for what might have oc curred. Among the items: Many features of the accident point to the possibility of the onset of uncontrolled reactions in MIC tank 610 through mixing with water or caustic. Water was discovered by workers af ter the accident when they drained the vent lines connecting the tank and the relief valve vent header. Also, caustic was found in the relief valve vent header. That many things were wrong with tank 610 is the easiest to confirm. At least from Nov. 30, the meters moni toring the tank were giving abnormally low pressure readings. A pressure of 20 psi is normal, but the meter on tank 610 was showing only 2 psi. It isn't known whether the cause was a faulty meter or inability of the tank to maintain pressure. It also isn't known whether efforts were made to check the condition of the rupture disk for tank 610. The pressure gage connected between the rupture disk and relief valve should indicate buildup of pres sure, but it needed to be monitored manually, since it wasn't linked to the control room or to a warning system. On Dec. 2, however, efforts were made to pressurize tank 610 by pump ing in nitrogen, but the control panel
Bhopal plant were sloppy and that enforcement of safety measures was lax. For example, the refrigeration system that should have cooled the MIC storage tank reportedly had been turned off to save electricity. The facts are still being assem bled. It will take a long time, at least in the courts, to unwind who was at fault for what at Bhopal. But Carbide, in hindsight, must certain
•
A
ω ο
οI "w I
Relief ω valve vent A. 2 header I %
3 |
en | Ο
Flare tower
Vent gas scrubber
!°
Relief , valve Gage (?)
ι Rupture disk assembly .
A
Pit
From MIC unit
To pesticide unit
*-
Refrig eration
Refrig- L j eration
MIC tank 611
Refrig eration
MIC tank 619
4J
Nitrogen pump reading didn't show a change. A sub sequent attempt was made to feed the Sevin plant from tank 610, but the attempt failed and the Sevin plant was fed instead from tank 6 1 1 . It's possible that the attempt to pres surize tank 610 created further dam age and may have caused the rupture disk to rupture. If the relief valve also was letting gas pass through, nitrogen could have escaped into the relief valve vent header and the pressure gage wouldn't have registered. If the rup ture disk and safety valves were faulty, they could have provided an entry path for small amounts of water, caustic solution, or gases into the storage tanks. If there was a buildup of reac
ly wish it had done some things differently, technologically speak ing. Because there were options. The main reason for making MIC is to use it as an intermediate in the manufacture of a variety of carba mate pesticides. The leading carba mate pesticide is Carbide's own in secticide Sevin (1-naphthyl-N-methylcarbamate), with the generic name carbaryl.
tions as a result, they would have been aided by a lack of chilling of the tank, since the refrigeration unit re portedly had been switched off as an economy measure. Once toxic gases were released uncontrollably, the underdesigned safe ty system could have at best neutral ized only a small part of the stored MIC. But the caustic pump was down, making it impossible to charge the vent gas scrubber once the small amount of caustic in it was exhausted. And the line connecting the vent gas scrubber and the flare tower meant for burning off unneutralized toxic gas was blanked off for repairs, since it had become heavily corroded.
The company says the details of the process it used to make MIC at Institute and at Bhopal are propri etary. However, it's known to be fairly simple and straightforward, as chemical processes go. The raw materials, methylamine and phos gene, are pumped into a reactor. There, with the application of heat, they form MIC and hydrogen chlo ride. The products are chilled; the February 11, 1985 C&EN
31
Rubber-Modified Thermoset Resins
C. Keith Riew, Editor The BF Goodrich Company John K. Gillham, Editor Princeton University Provides comprehensive coverage of rubber-modified thermoset resins. Presents various methods of modifica tion of thermoset resins, the consequent effects on the properties of the modified thermoset, and the development of the oretical and pragmatic approaches to characterize the various systems. Cov ers chemistry and physics of thermoset polymerization. CONTENTS Cross-Linking of Epoxy Resins · Transesterification and Gelation of Polyhydroxy Esters · Toughening of Epoxy Resins with Reactive Polybutadienes · Simultaneous Interpenetrating Networks · Rubber Toughening of Oxazolidinone-Modified Epoxy Novolacs · Character ization of a Carboxyl-Terminated Polybutadiene · Failure Behavior of Rubber-Tough ened Epoxies in Bulk, Adhesive, and Compos ite Geometries · Rubber-Toughened Polyimides · Effects of Monotonie and Cyclic Loading on Some Rubber-Modified Epoxies · Siloxane Modifiers for Epoxy Resins · An Al ternative Liquid Rubber for Epoxy Resin Toughening · Morphology and Dynamic Me chanical Behavior of Rubber-Toughened Ep oxy Resins · Model for Phase Separation Dur ing Thermoset Polymerization · Effect of Rubber Cross-Link Density and Tear Energy on the Toughness of Rubber-Modified Epoxies • Rubber-Modified Epoxies: Cure, Transition, and Morphology · Rubber-Modified Epoxies: Morphology, Transitions, and Mechanical Properties · Rubber-Modified, Flame-Retardant, High Glass Transition Temperature Epoxy Resins · Fluoroelastomer-Modified Thermo set Resins · Reaction Injection Molding of In terpenetrating Polymer Networks · Impact Properties of Rubber- Modified Epoxy ResinGraphite-Fiber Composites · Influence of Ma trix Toughening on the Impact Properties of In jection-Molded Sheet Molding Compound · Flame-Retardant Composition of Epoxy Res ins with Phosphorus Compounds Based on a symposium sponsored by the Division of Organic Coatings and Plastics Chemistry of the American Chemical Society Advances in Chemistry Series No. 208 374 pages (1984) Clothbound LC 84-21566 ISBN 0-8412-0828-X US & Canada $89.95 Export $107.95 Order from: American Chemical Society Distribution Office Dept. 23 1155 Sixteenth St., N.W. Washington, DC 20036 or CALL TOLL FREE 800-424-6747 and use your VISA, MasterCard, or American Express credit card.
32
February 11, 1985 C&EN
Bhopal Report gaseous hydrogen chloride is sepa rated in an absorber, and the liquid MIC goes to carbamate production or to storage. It should be noted that the MIC contains a small residual amount of phosgene. It helps inhibit the reac tion between MIC and water. It also inhibits polymerization. But it also should be noted that the phosgene provides a source of chlorine, and that most stainless steel alloys, a l t h o u g h generally chemically resistant, are rather vul nerable to attack by chloride ion. In theory, at least, that could lead to production of substances that could act as catalysts. In essence, the carbaryl process is even simpler. MIC and a-naphthol are mixed. They react to form carbaryl in high yield and with no by-products of consequence. That's not the only way to make carbaryl, however. An alternate method is first to react the a-naphthol with phosgene to form 1-naphthyl chloroformate and hydrogen chloride. Then the chloroformate is reacted with methylamine to form the carbamate and some more hy drogen chloride. That's the process that Carbide originally used when it started mak ing Sevin in 1958. The company had been making MIC since about 1957, mostly for the merchant mar ket but also for use in producing its own soil pesticide Temik (aldicarb). It changed to the MIC method for making Sevin in 1973. Asked the reason for the change, Carbide says only that "it was a superior process." However, it's not hard to think of some reasons. For one thing, it improved the logistics of making carbaryl and other carba mates. Although Sevin is far and away the best-selling carbamate pes ticide, Carbide also made Temik. It also made another carbamate insec ticide, methomyl, for Shell Chemi cal, which markets it under the name Nudrin. In addition to using MIC for its own manufactures, Carbide was the sole supplier of MIC to other com panies that used it to make their own carbamate pesticides. Du Pont, for example, used it to make Lannate (its brand of methomyl). FMC used it to make carbofuran, which is
marketed by it (and also by Mobay) under the name Furadan. And there were a number of other smallervolume customers. The arrangement must have been profitable for Car bide and, presumably, for its cus tomers as well. It also provided the incentive to maintain larger MIC inventories at Institute than other wise would have been needed for day-to-day operations there. In contrast, all the MIC made at Bhopal was for captive use there. However, it seems to have been the custom to keep relatively large amounts on hand, so that interrup tions in MIC production wouldn't affect carbaryl production. Nevertheless, carbamates can be made—and made using MIC as an intermediate—without keeping large stocks of MIC on hand. For exam ple, Bayer makes MIC in West Ger many and in Belgium, using it for the production of propoxur (o-isopropoxyphenyl- Ν -methylcarbamate), which Mobay Chemical imports and markets in the U.S. under the name Baygon. According to a Mobay spokesman, however, Bayer makes MIC by a different process in which dimethylurea and diphenyl carbon ate react at a fairly high tempera ture to form MIC. Phosgene—itself a rather hazardous chemical—isn't involved, the spokesman points out, adding that the Bayer process is car ried out at ambient pressure. Fur thermore, Bayer uses all the MIC almost immediately and doesn't ship it out of the plant. At La Porte, Tex., Du Pont has been scurrying to build a new unit to make MIC—by yet another pro cess—for use in the manufacture of Lannate. Du Pont declines to reveal much about its process, for propri etary reasons, but says that it in volves a reaction between methylformamide and air. The reaction pro duces water, but it is "stripped out" before MIC hydrolysis can get un der way. The MIC will be sent di rectly to the Lannate unit, with no side streams going to process stor age. Thus, at no time will there be more than about 20 lb of MIC in the closed-loop process stream. As chemicals go, methylformamide is fairly innocuous. Du Pont points out, however, that the chemical has been identified as a teratogen and
PROOUCT PROSPECTUS Bhopal Report embryotoxin, so it, too, requires care in handling. Specifically, pregnant women or even women of childbearing age mustn't be exposed to it. Du Pont says it began develop ment of the process in the late 1970s because it dislikes, on principle, to be dependent on sole-supplier ar rangements such as the one involv ing MIC from Carbide. However, the arrangement was satisfactory and the price was right, so there was no compelling reason to go ahead with the project, which will require a capital expenditure of $10 million to $12 million. Bhopal pro vided the reason. Target date for startup of the new unit is June 1. Carbide's suspension of MIC pro duction (and disposal of MIC stocks) won't have any immediate serious effects on supplies of carbamate pes ticides. Carbide itself, for example, says it has enough stocks on hand to last through the current growing season. Similarly, FMC says carbofuran production hasn't been inter rupted and that it has enough ma terials "to carry us well into 1985." Meanwhile, it's "looking at all op tions," from manufacturing its own MIC to getting other suppliers. Shell Chemical says it already had enough Nudrin and adds that it now has even more, as a result of Carbide's decision to dispose of MIC stocks, preferably by conversion to end products. Even if the MIC accident hasn't had an immediate impact on sup plies of carbamate pesticides, it has certainly focused a lot of attention on the general subject of safety in the chemical industry. For exam ple, Monsanto, very shortly after the Bhopal disaster, formed a se nior management task force to con duct a thorough review of safety policies and procedures at all com pany plants worldwide. If the re view turns up ways to improve the stringent safety policies already in force, they will be put into effect promptly, the company says. Other chemical companies, in cluding Dow Chemical, Du Pont, and American Cyanamid, also say they're taking another look, even as they emphasize that safety review is a continuing process. As one compa ny spokesman put it, Bhopal "has certainly increased our sensitivity." D
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