Isocyanate safety problems

Isocyanates have acute and chronic safety problems. Elimination of isocyanate vapors must in the first instance be carried out by engineering methods. The ventilation of the area must be good. Transfer of the isocyanates must, wherever possible, be automated so that there is no human contact. If there is handling by humans, the proper protective equipment should be worn. The personal protective equipment must include safety goggles, vapor mask, impervious gloves, and disposable overalls. If vapor levels are expected to be high, a self-contained breathing hood must be used. 

Phosgene is a very toxic chemical, and storage of it in large quantities poses a serious safety problem. A continuous tubular reactor is developed to make this chemical for immediate consumption. So an inventory of only 70 kg of gaseous phosgene has to be maintained when compared to an inventory of 25,000 kg of the liquid in the storage in the old batch process. Methyl isocyanate (MIC), the infamous chemical that was released at Bhopal, can be generated and immediately converted to the final pesticide in a tubular reactor that will contain a total inventory of less than 10 kg of MIC. 

The high reactivity of isocyanates together with their volatility gives rise to health and safety problems. A solution to volatility is to produce isocyanate-tipped PU pre-polymers, by reacting excess isocyanate with polyol under controlled conditions the oligomer can react with active hydrogen species some time later. This will also permit controlled development of the structure of a PU, especially when using mixtures of polyols. 

Before commencing any experimental work, the relevant up-to-date MSDSs must be studied and the appropriate safety requirements observed. There are often local or in-house regulations for handling certain materials such as MOCA. These must be strictly observed. All people near any isocyanate must take special care not to inhale any traces of its vapor, as these may cause respiratory problems. 

In 1984, one of the most notable process incidents occurred in Bhopal, India, at a plant owned by Union Carbide. On December 3, 1984, methyl isocyanate (MIC) was vented to the atmosphere from a vent gas scrubber after a run away reaction overwhelmed the scrubber. It is reported that more than 2500 people died and 20,000 people were injured as a result of exposure to MIC. The subsequent investigation showed that the run away reaction occurred in the MIC tanks after water was reportedly intentionally added to the tank. The safety systems, a pressure relief valve, a vent gas scrubber, and a flare were reportedly poorly maintained. The relief valve worked to vent the pressure, but the scrubber was overwhelmed, and the flare was down for maintenance. This incident highlighted several loss prevention areas that needed improvement. The first was mechanical integrity. No strong preventive maintenance effort appeared to be in place. The second was emergency preparedness and response. It appears that while the plant was built 1.5 miles away from the community, zoning problems allowed the community to expand to the plant limits. It does not appear that much effort was made to work with the community on commimication/notification or evacuation needs. ... 

Occupational illness and injury187 cost 30-40 billion dollars/yr in the United States.188 In 1994 there were 6.8 million injuries and illnesses in private industry, amounting to 8.4 cases per 100 workers. Nearly two-thirds were disorders associated with repeated trauma, such as carpal tunnel syndrome.189 The Occupational Safety and Health Act of 1970 set up the National Institute Safety and Health (NIOSH) to study the problem and the Occupational Safety and Health Administration (OSHA) to deal with it through inspections and regulations. Both have received so much criticism of their effectiveness that they are struggling to find more effective ways to deal with the problem.190 NIOSH is searching for practical ways to protect workers, especially those in small businesses from methylene chloride, tetrachloroethylene, diesel exhaust in coal mines, isocyanates, 2-methoxyethanol, and others. OSHA is about to expand a plan that worked well in Maine, a state that used to have one of the worst accident and illness records in the United States.191 The 200 firms with the worst records were asked to look for deficiencies and to correct them. They were also inspected. These measures cut injuries and illnesses over a 2-year period. 

The toxicity of phosgene has spawned a lot of research into alternates for both MDI and TDI, as well as polycarbonates. In addition to safety, there are economic incentives for developing alternate routes. In the conventional MDI process, methylene diphenylmethane diamine (MDA) is formed by reacting aniline with formaldehyde. Separating excess aniline from crude MDA is an expensive operation. Also, by-product HCl formed in the conversion of MDA to MDI is an environmental issue. The final isocyanate product contains hydrolyzable chloride compounds that are difficult to separate and dispose of. The reactants must be kept bone dry to prevent corrosion, and the introduction of water can cause a runaway reaction. Similar concerns influence the search for nonphosgene routes for TDl. Conventional routes to polycarbonates also employ phosgene, which produces chlorine waste products, primarily sodium chloride, that present disposal problems. The elimination of chlorine from the polycarbonate process would constitute a major improvement. 

Many people are familiar with the Bhopal disaster in December 1984, and as is usually the case, there were multiple problems and failures leading up to the catastrophic release of methyl isocyanate (MIC). For this case study, we will focus on the organizational issues related to personnel turnover to provide an example of how such changes can contribute to process safety incidents. 

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