Application of an inherently safer technology in the manufacture, handling, and storage of toxic chemicals will not necessarily result in elimination or optimal minimization of the associated hazard unless the application results in a clear, well-defined, and feasible path forward.
That’s one important finding in a new Congressionally-mandated report by the National Research Council (NRC) on an accident in 2008 involving methyl isocyanate (MIC) at a Bayer CropScience facility in West Virginia. MIC is a volatile, highly toxic chemical used in the manufacture of agricultural and residential pesticides. In 1984, a cloud of MIC gas from an explosion in Bhopal, India, killed nearly 3,800 people. The West Virginia incident resulted in the deaths of two employees and extensive damage to nearby structures. Although the storage container at the plant was not damaged, an investigation by the U.S. Chemical Safety and Hazard Investigation Board (CSB) found that debris could have struck a relief valve vent pipe and caused the release of MIC into the atmosphere. Bayer intended to restart production of the pesticides with MIC after plant modifications were complete, but decided in 2011 that it would cease production.
According to NRC, an inherently safer technology involves minimization or elimination of a hazard by using four strategies.
- Substitution - use materials, chemistry, or processes that are less hazardous.
- Minimization – use the smallest quantity of hazardous materials feasible for the process and/or reduce the size of equipment operating under hazardous conditions such as high temperature or pressure.
- Moderation - reduce hazards by dilution, refrigeration, or by locating hazardous facilities far from people or other property.
- Simplification – eliminate unnecessary complexity and design user-friendly plants.
NRC found that Bayer made use of inherently safer processing at the West Virginia facility, but concluded that inherently safety considerations were not explicitly stated in Bayer’s process safety management records.
“Bayer performed hazard and safety assessments and made business decisions which resulted in MIC inventory reduction, elimination of aboveground MIC storage, and adoption of various passive, active, and procedural safety measures,” states NRC. “However, these assessments did not explicitly incorporate the principles of minimization, substitution, moderation, and simplification that form the basis of inherently safer processes.”
In general, NRC was also concerned that as inherently safer process analysis is currently performed, it may become too narrowly focused and as a consequence may overlook certain outcomes. “Even when multiple outcomes are recognized, they may be inappropriately weighted,” sates NRC. “For example existing indexes for assessing inherently safer processes cannot capture the preferences of all decision makers, and the many trade-offs, uncertainties, and risk tolerances are hidden from view as implicit assumptions rather than explicit chosen parameters.”
NRC recommends that CSB or another appropriate entity convene a working group to identify obstacles to employing methods from the decision sciences in process safety assessments. “[The working group] should identify options for tailoring these to the chemical process industry and incentives that would encourage their use.”
Information on NRC’s report, The Use and Storage of Methyl Isocyanate (MIC) at Bayer CropScience, is at http://www.nap.edu/catalog.php?record_id=13385.