Safety of Plant and Environment

TABLE 1A Safety Factors in Equipment Design Results of a Questionnaire 

Equipment Design Veriable Range of Safety Factor %) 

It is not often that proper estimates can be made of uncertainties of all the parameters that influence the performance or required size of particular equipment, but sometimes one particular parameter is dominant. All experimental data scatter to some extent, for example, heat transfer coefficients and various correlations of particular phenomena disagree, for example, equations of state of liquids and gases. The sensitivity of equipment sizing to uncertainties in such data has been the subject of some published information, of which a review article is by Zudkevich Encycl. Chem. Proc. Des. 14, 431-483 (1982)] some of his cases are  

Sizing of isopentane/pentane and propylene/propane splitters. 

Effect of volumetric properties on sizing of an ethylene compressor. 

Equipment Design Variable Range of Safety Factor (%) 

Heat exchangers, shell and tube for liquids area 11-18 

The safe practices described in the previous section are primarily for assurance that the equipment have adequate performance over anticipated ranges of operating conditions. In addition, the design of equipment and plant must minimize potential harm to personnel and the public in case of accidents, of which the main causes are 

A more nearly complete list of potential hazards is in Table 1.4, and a checklist referring particularly to chemical reactions is in Table 1.5. 

Examples of common safe practices are pressure rehef valves, vent systems, flare stacks, snuffing steam and fire water, escape hatches in explosive areas, dikes around tanks storing hazardous materials, turbine drives as spares for electrical motors in case of power failure, and others. Safety considerations are paramount in the layout of the plant, particularly isolation of especially hazardous operations and accessibility for corrective action when necessary. 

Continual monitoring of equipment and plant is standard practice in chemical process plants. Equipment deteriorates and operating conditions may change. Repairs are sometimes made with materials or equipment whose ultimate effects on operations may not have been taken into account. During start-up and shutdown, stream compositions and operating conditions are much different from those under normal operation, and their possible effect on safety must be considered. Sample checkhsts of safety questions for these periods are in Table 1.6. 

Detailed safety checklists appear in books by Fawcett and Wood (1982) and Wells (1980). These books and the volume by Lees (1996) also provide entry into the vast hterature of chemical 

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SAFETY OF PLANT AND ENVIRONMENT 7 TABLE 1.4. Safety Factors in Equipment Design Results of a Questionnaire... 

Operate plants in a way that protects the environment and the health and safety of workers and the public. 

The supreme principle of plant and process safety is to devise processes and plants such that they do not cause considerable dangers for man, environment and valuable assets [2]. This is to be achieved by a design based on the state of technology, respectively of safety technology, which is represented by numerous statutory regulations, standards, ndes and guidelines (cf. [3]). These refer to both the components of technical plants and to the plants themselves [4, 5]. 

Safety-related controllers in conjunction with safety or fail safe I/O modules are used for critical and hazardous applications where an incident can result in danger to persons, and/or damage to plant and environment. These safety-related controllers can work with the safety-related distributed I/O system (may be with internal verification for input or output via safety switches as described in Clause 5.0.1—safe PLC approach), or directly with fail-safe transmitters cormected via the fieldbus. These controllers are supposed to detect faults both in the process and their own internal (self-diagnosis) to the system. It is the duty of the same to automatically set the plant to a safe state in the event of a fault. These controllers need to work in multitasking environment — may be in a mix of standard BPCS or safety-related applications, if integrated operation is permitted by the end-user. The programs of BPCS and SIS must be functionally separate, so that faults in BPCS applications have no effect on safety-related applications and vice versa. Special tasks with very short response times can also be implemented [14]. For safety applications controllers and I/O modules need to individually certified by third party and to comply SIL 2/SIL 3 (as the case may be — SIL 4 only for nuclear application) as per lEC 61508. For safety-related applications a few restrictions are followed such as ... 

The rest of section 2 puts a bit more flesh on the general duty expressed in section 2(1). Important requirements in the context of electrical safety include the provision of plant and systems of work that are safe the provision of information, instruction, training, and supervision as necessary the maintenance of places of work in a safe condition and the provision and maintenance of a safe and healthy working environment. 

In selecting materials for petrochemical plants, considerable effort should be paid to fluid composition, sizing of lines, valve and pump details, and processing temperature and pressure. Most environments in petrochemical processes involve flammable hydrocarbon systems, highly toxic chemicals, explosive gases, and strong acids and caustics. Therefore corrosion could be a mysterious and costly enemy to the safety of personnel and community. 

The accident at the Three Mile Island (TMI) plant in Pennsylvania in 1979 led to many safety and environmental improvements (4—6). No harm from radiation resulted to TMI workers, to the pubHc, or to the environment (7,8), although the accident caused the loss of a 2 x 10 investment. The accident at the Chernobyl plant in the Ukraine in 1986, on the other hand, caused the deaths of 31 workers from high doses of radiation, increased the chance of cancer later in life for thousands of people, and led to radioactive contamination of large areas. This latter accident was unique to Soviet-sponsored nuclear power. The Soviet-designed Chemobyl-type reactors did not have the intrinsic protection against a mnaway power excursion that is requited in the test of the world, not was there a containment building (9—11). 

Technical and trade organi2ations are concerned with safety and the environment. The Chlorine Institute in North America and Euro Chlor in Western Europe are examples of organi2ations dedicated to the safe production, transport, and use of chlorine. Ha2ard and operabiHty studies (HAZOP) reviews for new designs, plants, and expansions (135) have become required by poHcy in many operating companies. Papers on safety and environmental subjects are given at most technical meetings (136—138). 

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