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Introduction to Risk Analysis of Fine Chemical Processes

Case History

A multipurpose reactor was protected against overpressure by a rupture disk, which lead directly to the outside through the roof of the plant. During a maintenance operation, it was discovered that this disk was corroded. Although it was decided to replace it, there was no spare part available. Since the next task to be carried out was a sulfonation reaction, it was decided to leave the relief pipe open without the rupture disk in place. In fact, a sulfonation reaction is unlikely to lead to overpressure (sulfuric acid only starts to boil above 300?°C), so such a protection device should not be required. During the first batch a plug of sublimate formed in the relief line. This went unnoticed, and production continued. After heavy rain, water entered the relief tube and accumulated above the sublimate plug. As the next batch began, the plug heated and suddenly ruptured, allowing the accumulated water to enter the reactor. This led to an abrupt exothermal effect, due to the dilution of concentrated sulfuric acid. The increase in temperature triggered sudden decomposition of the reaction mass, causing the reactor to burst, resulting in huge damage.

Lessons Drawn

This type of incident is difficult to predict. Nevertheless, by using a systematic approach to hazard identification, it should become clear that any water entering the reactor could lead to an explosion. Therefore when changing some parts of the equipment, even if they are not directly involved in a given process, especially in multipurpose plants, one should at least consider possible consequences on the safety parameters of the process.

Introduction

Systematic searches for hazard, assessment of risk, and identification of possible remediation are the basic steps of risk analysis methods reviewed in this chapter. After an introduction that considers the place of chemical industry in society, the basic concepts related to risk analysis are presented. Section 1.2 reviews the steps of the risk analysis of chemical processes discussed. Safety data are presented in Section 1.3 and the methods of hazard identification in Section 1.4. The chapter closes with a section devoted to the practice of risk analysis.

1.1 Chemical Industry and Safety

The chemical industry, more than any other industry, is perceived as a threat to humans, society, and the environment. Nevertheless, the benefits resulting from this activity cannot be negated: health, crop protection, new material, colors, textiles, and so on. This negative perception is more enhanced after major accidents, such as those at Seveso and Bhopal. Even though such catastrophic incidents are rare, they are spectacular and retain public attention. Thus, a fundamental question is raised: "What risk does society accept regarding the benefits of an activity, of a product?" Such a question assumes that the corresponding risk can be assessed a priori.

In the present chapter, we focus on the methods of risk analysis as they are performed in the chemical industry and especially in fine chemicals and pharmaceutical industries.

1.1.1 Chemical Industry and Society

The aim of the chemical industry is to provide industry and people in general with functional products, which have a precise use in different activities such as pharmaceuticals, mechanics, electricity, electronics, textile, food, and so on.

Thus, on one hand, safety in the chemical industry is concerned with product safety, that is, the risks linked with the use of a product. On the other hand, it is concerned with process safety, that is, the risks linked with manufacturing the product. In this book, the focus is on process safety.

1.1.1.1 Product Safety

Every product between its discovery and its elimination passes through many different steps throughout its history: conception, design, feasibility studies, market studies, manufacturing, distribution, use, and elimination, the ultimate step, where from functional product, it becomes a waste product [1].

During these steps, risks exist linked to handling or using the product. This enters the negative side of the balance between benefits and adverse effects of the product. Even if the public is essentially concerned with the product risks during its use, risks are also present during other stages, that is, manufacture, transportation, and storage. For pharmaceutical products, the major issues are secondary effects. For other products, adverse effects are toxicity for people and/or for the environment, as well as fire and explosion. Whatever its form, once a product is no longer functional, it becomes a waste product and thus represents a potential source of harm.

Therefore, during product design, important decisions have to be made in order to maximize the benefits that are expected from the product and to minimize the negative effects that it may induce. These decisions are crucial and often taken after a systematic evaluation of the risks. Commercialization is strictly regulated by law, and each new product must be registered with the appropriate authorities. The aim of the registration is to ensure that the manufacturer knows of any properties of its product that may endanger people or the environment and is familiar with the conditions allowing its safe handling and use, and finally safe disposal at the end of the product's life. Thus products are accompanied by a material safety data sheet (MSDS) that summarizes the essential safety information such as product identity, properties (toxicity, ecotoxicity, chemical, and physical properties), information concerning its life cycle (use, technology, exposure), specific risks, protection measures, classification (handling, storage, transportation), and labeling.

1.1.1.2 Process Safety

The chemical industry uses numerous and often complex equipment and processes. In the fine chemical industries (including pharmaceuticals), the plants often have a multipurpose character, that is, a given plant may be used for different products. Inversely a given process may be performed in different plant units, leading to a great number of possible combinations. Moreover, when we consider a chemical process, we must do it in an extensive way, including not only the synthesis itself but also the workup by physical unit operations and finally also storage and transportation. This comprises not only the product but also the raw material.

Risks linked with chemical processes are diverse. As already mentioned, product risks include not only toxicity, flammability, explosion, and corrosion but also additional risks due to chemical reactivity. A process often uses conditions (temperature, pressure) that by themselves may present a risk and may lead to deviations, which can generate critical effects. The plant equipment, including its control equipment, may also fail. Finally, since fine chemical processes are work intensive, they may be subject to human error. Therefore, all of these elements, that is, chemistry, energy, equipment, and operators and their interactions, constitute the object of process safety.

1.1.1.3 Accidents and Risk Perception in Chemical Industry

Despite some incidents, the chemical industry presents good accident statistics. A statistical survey of work accidents shows that chemistry is positioned at the end of the list, classified by order of decreasing lost work days [2] (Table 1.1). Further, only a minor part of these accidents is due to chemical accidents, the greatest part consisting of common accidents such as falls, cuts, and so on that can happen in any other activity.

Another instructive comparison can be made by comparing fatalities in different activities. Here we use the fatal accident rate (FAR) index that gives the number of fatalities for 108 h of exposure to the hazard [3, 4]. Some activities are compared in Table 1.2. This shows that even with better statistics in terms of work accidents and fatalities, industrial activities are perceived as presenting higher risks. This may essentially be due to the risk perception. The difference in perception is that for traveling or sporting activities, the person has the choice whether to be exposed or not, whereas for industrial activities, exposure to risk may be imposed. Industrial risks may also impinge on people who are not directly concerned with the activity. The pressure wave or toxic release may impact people living in the vicinity of a chemical plant. The lack of information on what goes on in an industrial site or the lack of technical knowledge induces a fear from the unknown and biases the risk perception [5].

Table 1.1 Accidents at work in different activities in Switzerland, from the statistics of the Swiss National Accident Insurance (2016).