Accident chemical plant

Accidents in chemical plants make headline news, especially when there is loss of hfe or the general public is affected in even the slightest way. This increases the public s concern and may lead to government action. The terms hazard and risk are defined as follows ... 

Control of Plant and Process Modifications Many accidents have occurred because plant or process modifications had unforeseen and unsafe side effects (Sanders, Management of Change in Chemical Plants Learning from Ca.se Histories, Butterworth-Heinemann, 1993). No such modifications shoiild therefore be made until they have been authorized by a professionally quahfied person who has made a systematic attempt to identify and assess the consequences of the proposal, by hazard and operability study or a similar technique. When the modification is complete, the person who authorized it... 

Risk indices are usually single-number estimates, which may be used to compare one risk with another or used in an absolute sense compared to a specific target. For risks to employees the fatal accident rate (FAR) is a commonly apphed measure. The FAR is a singlenumber index, which is the expected number of fatalities from a specific event based on 10 exposure hours. For workers in a chemical plant, the FAR could be calculated as follows ... 

Dale, S. E. (1987). Cost Effective Design Considerations for Safer Chemical Plants. Proceedings of the International Symposium on Preventing Major Chemical Accidents, February 3-5, 1987, Washington, D. C., ed. J. L. Woodward, 3.79-3.99. New York American Institute of Chemical Engineers. 

While event trees are not so common in chemical plant PSA they are extensively used to analyze nuclear accidents, but before beginning the analysis, preliminaries that are needed are plant tamiliarity and initiator selection... 

An explosion and fire at an Albright Wilson Americas phosphorus chemicals plant in Charleston, SC (June 17, 1991) killed six and injured 33. The damaged unit lost part of its walls and roof Eight other units on the 200 employee site, sustained minor or no damage, but were shutdown for a few days. At the time of the accident, plant workers were mixing chemicals in the No. 2 reactor in the special products unit when an explosion and fire occurred. Five of the people killed were contract employees not directly involved with the reactor, but were installing insulation nearby. 

On chemical plants and oil refineries, steam, nitrogen, compressed air. lubricating oil, and other utility systems are responsible for a disproportionately large number of accidents. Flammable oils are recognized as a hazard, but services are given less attention. If the modification to the lubricating system had been systematically studied before it was made, as recommended in Chapter 2, a larger vent could have been installed, or a pipe-break and funnel could have been installed at the inlet to the sump. 

Lewis (1989) describes the accident, which occurred in Siberia on the night of June 3 and early hours of June 4, 1989. Late on June 3, 1989, engineers in charge of the 0.7 m (28 in.) pipeline, which carried natural gas liquids from the gas fields in western Siberia to chemical plants in Ufa in the Urals, noticed a sudden drop in pressure at the pumping end of the pipeline. It appears that the engineers responded by increasing the pumping rate in order to maintain normal pipeline pressure. 

The probability tliat an accident will occur has to be determined. For e.Nample, if a chemical plant has a given life, what is tlie probability that the temperature in a reactor will exceed the specified temperature range The probability can be ranked qualitatively from low to high. A low probability means tliat it is unlikely for tlie event to occur in tlie life of the plant. A medium probability suggests tliat tlicre is a probability that tlie event will occur. A liigli probability means that the event will probably occur during the life of the plant. 

The event or scries of events that will initiate an accident has to be identified. An event could be a failure to follow correct safety procedures, improperly repaired equipment, or a safety mechanism The probability tliat tlie accident will occur lias to be determined. For e.xample, if a chemical plant has a 10-year life, wliat is the probability that... 

In case of an accident at a chemical plant, who will warn local residents about toxic emissions and provide for appropriate protection ... 

The minimiziiig/prevendon of accidents in a chemical plant calls for a detailed study of plant site and layout, materials, processes, operations, equipment, and training, plus an effective loss prevention program. 

You liave been hired as a consultant to a company administrator who has a limited budget for die mitigation of hazards in a certain chemical plant. The plant employs two kinds of workers day employees tliat work one 8 hour sliLft daily, and sliift employees that rotate tlirougli tliree 8 hour shifts each day. A HAZOP-HAZAN report reveals two kinds of accidents are possible during plant operation. 

A number of environmental issues have received widespread publicity (Table 7.1), from major accidents at plants (e.g., Seveso and Bhopal) to the global and regional impacts associated with energy utilization (e.g., carbon dioxide, acid rain, and photochemical oxidants), the improper disposal of chemical waste (e.g., Love Canal and Times Beach), and chemicals that have dispersed and bioaccumulated affecting wildlife (e.g., PCBs and DDT) and human health (e.g., cadmium, mercury, and asbestos). 

Safety or loss prevention the prevention of accidents through the use of appropriate technologies to identify the hazards of a chemical plant and eliminate them before an accident occurs. 

As will be shown later, chemical plants are the safest of all manufacturing facilities. However, the potential always exists for an accident of catastrophic proportions. Despite substantial safety programs by the chemical industry, headlines of the type shown in Figure 1-1 continue to appear in the newspapers. 

Recognizing that the chemical industry is safe, why is there so much concern about chemical plant safety The concern has to do with the industry s potential for many deaths, as, for example, in the Bhopal, India, tragedy. Accident statistics do not include information on the total number of deaths from a single incident. Accident statistics can be somewhat misleading in this respect. For example, consider two separate chemical plants. Both plants have a probability of explosion and complete devastation once every 1000 years. The first plant employs a single operator. When the plant explodes, the operator is the sole fatality. The second plant employs 10 operators. When this plant explodes all 10 operators succumb. In both cases the FAR and OSHA incidence rate are the same the second accident kills more people, but there are a correspondingly larger number of exposed hours. In both cases the risk taken by an individual operator is the same.4... 

Some naturalists suggest eliminating chemical plant hazards by returning to nature. One alternative, for example, is to eliminate synthetic fibers produced by chemicals and use natural fibers such as cotton. As suggested by Kletz,8 accident statistics demonstrate that this will result in a greater number of fatalities because the FAR for agriculture is higher. 

Table 1-6 Three Types of Chemical Plant Accidents...

Chemical plant accidents follow typical patterns. It is important to study these patterns in order to anticipate the types of accidents that will occur. As shown in Table 1-6, fires are the most common, followed by explosion and toxic release. With respect to fatalities, the order reverses, with toxic release having the greatest potential for fatalities. 

Figure 1-6 Types of loss for large hydrocarbon-chemical plant accidents. Source Large Property Damage Losses in the Hydrocarbon-Chemical Industries A Thirty-Year Review (New York Marsh Inc., 1998), p. 2. Used by permission of Marsh Inc.

Figure 1-7 presents the causes of losses for the largest chemical accidents. By far the largest cause of loss in a chemical plant is due to mechanical failure. Failures of this type are usually due to a problem with maintenance. Pumps, valves, and control equipment will fail if not properly maintained. The second largest cause is operator error. For example, valves are not opened or closed in the proper sequence or reactants are not charged to a reactor in the correct order. Process upsets caused by, for example, power or cooling water failures account for 11 % of the losses. 

Accidents follow a three-step process. The following chemical plant accident illustrates these steps. 

The Flixborough accident is perhaps the most documented chemical plant disaster. The British government insisted on an extensive investigation. 

X T. M-ost accidents in chemical plants result in spills of toxic, flammable, and explosive materials. 

The three most common chemical plant accidents are fires, explosions, and toxic releases, in that order (see chapter 1). Organic solvents are the most common source of fires and explosions in the chemical industry. 

Accidents in chemical plants are usually the result of a complicated interaction of a number of process components. The overall process failure probability is computed from the individual component probabilities. 

We hope that this textbook helps prevent chemical plant and university accidents and contributes to a much safer future. 

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