Safe design

The introdrrction to the code sets forth engineering reqrrirements deemed necessary for the safe design and constrrrction of piping systems. While safety is the basic consideration of the code, this factor alone will not necessarily govern final specifications for any pressrrre piping system. 

Evidently a temperature rise of 7 C would not be a safe design because the equilibrium line nearly touches the operating line near the bottom of the tower, creating a pinch. A temperature rise of 6 C appears to give an operable design, and for this case Lki = 349 kmol per 100 kmol of feed gas. 

Instrumentation (Arthur D. Little, Inc., and Levine, 1986.) Instrument systems are an essential part of the safe design and operation of systems for storing and handling highly toxic hazardous materials. They are key elements of systems to eliminate the threat of conditions that could result in loss of containment. They are also used for early detection of releases so that mitigating ac tion can be taken before these releases result in serious effects on people in the plant or in the public sector, or on the environment. 

The Center for Chemical Process Safety (CCPS) has identified the need for a publication dealing with process safety issues unique to batch reaction systems. This book, Guidelines for Process Safety in Batch Reaction Systems, attempts to aid in the safe design, operation and maintenance of batch and semi-batch reaction systems. In this book the terms batch and semi-batch are used interchangeably for simplicity. The objectives of the book are to ... 

Frequently a piece of equipment is used in different processes during its lifecycle. This could result in process conditions that exceed the safe operating limits of the equipment. Equipment inspection may provide a poor prediction of the equipment s useful life and reliability, due to the change of material handled or change in process chemistry over the life of equipment. Batch operations are also characterized by frequent start-up and shut-down of equipment. This can lead to accelerated equipment aging and may lead to equipment failure. This chapter presents issues and concerns related to the safe design, operation, and maintenance of various pieces of equipment in batch reaction systems, and provides potential solutions. 

Wilday, A.J. 1991. The Safe Design of Chemical Plants with No Need for Pressure Relief Systems. Elazards IX—New Directions in Process Safety. IChemE Symposium Series. No. 124, pp. 243-253. Institute of Chemical Engineers, IChemE, Rugby, U.K. 

Eail-Safe Design features which provide for the maintenance of safe operating conditions in the event of a malfunction of control devices or an interruption of an energy source (e.g., direction of failure of a control valve on loss of signal). A system is fail-safe if failure of a component, signal, or utility that would create a hazard initiates an action that maintains the system in a safe condition. 

The material properties of window glass are summarised in Table 18.1. To use these data to calculate a safe design load, we must assign an acceptable failure probability to the window, and decide on its design life. Failure could cause injury, so the window is a critical component we choose a failure probability of 10The vacuum system is designed for intermittent use and is seldom under vacuum for more than 1 hour, so the design life under load is 1000 hours. 

In support of the development of graphite moderated reactors, an enormous amount of research has been conducted on the effects of neutron irradiation and radiolytic oxidation on the structure and properties of graphites. The essential mechanisms of these phenomena are understood and the years of research have translated into engineering codes and design practices for the safe design, construction and operation of gas-cooled reactors. 

Where possible plants of intrinsleahy safe design are prefeiTed, i.e. those whieh have been designed to be self-eorreeting rather than those where equipment has been added on to eontrol hazards. Some eharaeteristies of intrinsleahy safe plants are ... 

Tube failure in a water-cooled or steam-heated exchanger used in hydrocarbon service can result in the contamination of the effluent cooling water or the condensate by the process stream, especially if the latter is at a higher pressure. Such effluents must be disposed of in such a maimer that the hydrocarbon contaminations can be safely contained. The following are some safe design practices ... 

The safe design and operation of chemical processing equipment requires detailed attention to the hazards inherent in certain chemicals and processes. Chemical plant hazards can occur from many sources. Principal hazards arise from ... 

Fail-safe Design features that provide for the maintenanee of safe operating eonditions in the event of a malfunetioning eontrol deviee or an interruption of an energy souree (e.g., direetion of failure of a motor-operated valve on loss of motor power). 

Dutt, S. (1996). Safe Design of Direct Steam Injection Heaters. 5th World Congress of Chemical Engineering, July 14-18, 1996, San Diego, CA, Paper 52c. New York American Institute of Chemical Engineers. 

Windhorst, J. C. A. (1995). Application of Inherently Safe Design Concepts, Fitness for Use and Risk Driven Design Process Safety Standards to an LPG Project."loss Prevention and Safety Promotion in the Process Industries, ed. J. J. Mewis, H. J. Pasman, and E. E. De Rademacker, 543-54. Amsterdam Elsevier Science B. V. 

To develop a safe design, it is necessary to first design and specify all equipment and systems in accordance with applicable codes and standards. Once the system is designed, a process safety shutdown system is specified to assure that potential hazards that can be detected by measuring process upsets are detected, and that appropriate safety actions (normally an automatic shutdown) are initiated. A hazards analysis is then normally undertaken to identify and mitigate potential hazards that could lead to fire, explosion, pollution, or injury to personnel and that cannot be detected as process upsets. Finally, a system of safety management is implemented to assure the system is operated and maintained in a safe manner by personnel who have received adequate training. 

D. K. McKibben, Safe Design of Atmospheric Pressure Vessels, Paper presented at Seminar on Prevention of Fires and Explosions in the Hydrocarbon Industries, Institute of Gas Technology, Chicago, June 21-26, 1982. 

Bellamy, L. J., Geyer, T. A. W. (1988). Addressing Human Factors Issues in the Safe Design and Operation of Computer Controlled Process Systems. In B. A. Sayers (Ed.), Proceedings ofSARSS 88. Human Factors and Decision Making Their Influence on Safety and Reliability. 19-20 October, Altrincham, Manchester, U.K. London Elsevier Applied Science. 

Very low velocities U ill allow particles to drift through the mesh and be carried out with the lea dng vapor. Also, very high velocities will carry liquid to the top of the mesh, establish a flooding condition, and then reentrain the lit]uid from the surface of the mesh. For most situations very good performance can be expected for all velocities from 30% to 100% of the optimum allowable design velocity. The minimum allowable safe design velocity is 10 percent of the value calculated by the equation. The flooding velocity of the mesh is usually about 120 percent to 140 percent of the maximum allowable velocity. 

T. Kletz, Process Plants A Handbook for Inherently Safe Design , Taylor Francis, London, 1998. 

More detailed check lists are given by Carson and Mumford (1988) and Wells (1980). Balemans (1974) gives a comprehensive list of guidelines for the safe design of chemical plant, drawn up in the form of a check list. A loss prevention check list is included in the Dow Fire and Explosion Index Hazard Classification Guide, Dow (1987). 

Balemans, A. W. M. (1974) Check-lists guide lines for safe design of process plants. Loss Prevention and Safety Promotion in the Process Industries, C. H. Bushmann (ed.) (Elsevier). 

This value is also taken as the mean density of the fluid in the downcomer which means that for safe design the clear liquid back-up, calculated from equation 11.91, should not exceed half the plate spacing lt, to avoid flooding. 

They are important aspects to be considered in new construction on land where protective or radon safe design is recommended. 

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