Inherently safer processes for the chemical industry

December 3, 1984 is an infamous day. It is so for the thousands who lost their lives, the many more maimed – some for life – and for the chemical industry. The leakage of methyl isocyanate (MIC) in the early hours of the day, when the teeming masses living cheek-by-jowl to the pesticides plant of Union Carbide in Bhopal, were mostly asleep, was a disaster of epic proportions, with few parallels in the history of industrial development.

The cause of the accident still remains clouded in mystery. While the official report cites the unintended ingress of Water (and there are a few theories how this happened) into a storage tank that contained about 40-tonnes of MIC, unsubstantiated theories of sabotage were also floated, very possibly to deflect blame from the plant owners. But what became clear in the weeks and months after the disaster was that the plant and the safety systems were allowed to fall into disrepair as the business was floundering. In short, a disaster waiting to happen!

Lessons from Bhopal

Much has been learned from this tragedy, and thankfully there has not been another disaster anything like Bhopal. The discipline of process safety saw renewed interest following the accident. The Responsible Care doctrines were formulated soon after in Canada, to assuage society’s concerns over the hazards and risks the chemical industry poses. Zoning laws were reframed to accommodate this vital industry in distant and safe locations. Plant safety and maintenance – hitherto relegated as costs to reluctantly bear – began to receive the attention it never had. Emergency planning and preparedness – fine tuned by repeated drills and modelling studies – became the norm at major plants.

One of the important concepts to emerge from the accident was the concept of inherent safety – built by design into a chemical plant. This idea has since extended beyond the chemical industry into the nuclear industry, though scepticism of the latter continues, especially in the developed world. But the chemical industry’s acceptance of this approach has been less than whole-hearted.

What is inherently safer design?

It is now startlingly obvious that by the sheer storage of 40-tonnes of a highly reactive and toxic material, the Bhopal plant was inherently unsafe. Even more due the fact that MIC was neither a starting raw material nor a finished product, but an intermediate that need not have to be stored at all. And this when an alternate route, to the pesticide (Carbaryl) was well known.

That chemical plants pose hazards and hence risks is a given. The question is about managing them to the best of ones ability, and with the technologies on hand. In conventional plants control of risks is achieved through proactive systems, which reduce the likelihood of hazards being realised, and mitigating systems that reduce their severity. As amply evident in Bhopal, these can fail for several reasons – misuse, disuse, repair or even malfeasance. In contrast, in inherently safer plants, the hazards – and consequently the risks – are identified early in the process development and plant design phase, and avoided or minimised.

An ‘inherently safer’ approach to hazard management is one that tries to avoid or eliminate hazards, or reduce their magnitude, severity, or likelihood of occurrence, by careful attention to the fundamental design and layout. Less reliance is placed on ‘add-on’ engineered safety systems and features, and procedural controls, which can and do fail.

The concept is in sync with some of the Principles of Green Chemistry and Engineering: the emphasis on less hazardous chemical syntheses routes; the design and use of safer chemicals; use of safer solvents & auxiliaries; design for energy efficiency; use of catalytic reagents, rather than stoichiometric amounts; designing for degradation in the environment; and the use of inherently safer chemistry.

Why the need?

The changes in the global chemical industry, especially since the 1990s, makes it all the more important to opt for inherently safer processes. The migration of the industry eastwards to the populous countries of Asia – China, India, Indonesia etc. – has increased hazards due crowding. Nearly 20% of the total population of Bhopal lived in the slum colonies within 5-km of the pesticide plant. Zoning laws in several emerging economies are poorly legislated and/or implemented.

To add to the problems, safety regulations in several developing countries are at times inappropriate, non-existent, or just poorly implemented for a variety of reasons, including the lack of adequate capacity. These deficiencies are less of a problem when the plants are relatively new or when profitability is good, but the passage of time and rising competitive pressures bring shortcomings to the fore.

Another reason to opt for inherently safer plants is their growing size. Plants being built today are typically larger than in the past, to reap economies of scale and because the market opportunity is also much larger in emerging economies. While the design for these plants have been exported from the west, they are typically not optimised or adapted to the location they are now being built. Studies have shown that the individual risk of the most exposed person in an ethylene plant, for instance, increases with the capacity raised to the power of 1.33, and with the square of the capital investment.

Benefits of inherently safer design

There are many examples of inherent safety being applied across the process industry. The case of non-phosgene routes to isocyanates (MIC is one) is an example. The move away from flammable solvents in the paints sector, which not only reduces health hazards during use of paint products, but also eliminating the fire and explosion hazards during manufacture, is another.

Inherently safer plant design would imply that the risk control would not be so dependent on regulation, operator training, protective systems etc. From a security and terrorism angle too such designs have advantages, especially in countries where the terrorism threat perceptions are high and the response mechanisms still under-developed (which could apply to much of the world).

Why then are such plants not the norm?

While inherently safer plant design is a philosophy that is easy to understand and Admire, it is not widely practiced. Some of the reasons for this can be traced to the conservative nature of the chemical industry and its aversion to commercial risk, but other factors play a part too:

Not enough in itself

While scientists and engineers have made great strides in understanding the impacts of industrial processes and products over the past several decades, there is still no guaranteed formula for developing inherently safer production processes. In the future, chemical and related industries will benefit greatly from increased educational and professional development and training of scientists and engineers in the disciplines of green chemistry and engineering, risk analysis, and industrial ecology.

While safer plant design will have an important role to play in improving society’s acceptance of the chemical industry, it is important to realise that chemical manufacturing still has inherent hazards and risks that will need to be managed. Reducing exposure to the hazards is as crucial as minimising it, and starts with clear zoning of the industry away from populated centres. The Indian government’s decision to create dedicated zones for the industry – the so-called Petroleum, Chemicals and Petrochemicals Investment Regions (PCPIRs) – need to be seen in this context as well, in addition to their economic rationale. The plans to fine-tune the policy in the light of its failure to lure investments over the last decade needs to be fast-tracked.

An overwhelming focus in design on speed-to-market and costs;Inadequate tools to assess inherent safety;Inflexible methods for capital and operating cost estimation and economic feasibility assessment, that do not credit inherently safer designs with their cost advantages;No enforced legislative requirements for inherently safer plant; andLack of incentives for implementing inherently safer designs.