Guidelines for Engineering Design for Process Safety

• Éditeur: Wiley-AIChE
• Année: 2012
• ISBN:
  9781118265468
• Édition: 2
• Sujet: Tecnología e ingeniería
• Sous-sujet: Ingeniería química y bioquímica

This updated version of one of the most popular and widely used CCPS books provides plant design engineers, facility operators, and safety professionals with key information on selected topics of interest. The book focuses on process safety issues in the design of chemical, petrochemical, and hydrocarbon processing facilities. It discusses how to select designs that can prevent or mitigate the release of flammable or toxic materials, which could lead to a fire, explosion, or environmental damage.

Key areas to be enhanced in the new edition include inherently safer design, specifically concepts for design of inherently safer unit operations and Safety Instrumented Systems and Layer of Protection Analysis. This book also provides an extensive bibliography to related publications and topic-specific information, as well as key information on failure modes and potential design solutions.

CHAPTER 1

INTRODUCTION

The Center for Chemical Process Safety (CCPS) has published a number of guidelines that focus on the evaluation and mitigation of risks associated with catastrophic events in process facilities. Originally published in 1993, the purpose of Guidelines for Engineering Design for Process Safety was to shift the emphasis on process safety to the earliest stage of the design where process safety issues could be addressed at the lowest cost and with the greatest effect. Almost 20 years later, this 2^nd edition of Guidelines for Engineering Design for Process Safety continues to stress the importance of emphasizing process safety during Front-End Engineering and Design (FEED) to achieve the greatest risk reduction at the lowest cost – and also emphasizes the benefits of diligence to process safety design issues through the life of the facility. This updated book also incorporates material from Guidelines for Design Solutions for Process Equipment Failures, which was originally published by CCPS in 1998 (Ref. 1–1).

This book focuses on process safety issues in the design of chemical, petrochemical, and hydrocarbon processing facilities. Enough information is provided on each topic to ensure that the reader understands:

• The concept and issues
• The design approach for process safety
• Areas of concern
• Where to go for detailed information

The scope of this book includes avoidance and mitigation of catastrophic events that could impact people and facilities in the plant or surrounding area. The scope is limited to selecting appropriate designs to prevent or mitigate the release of flammable or toxic materials that could lead to a fire, explosion, and impact to personnel and the community. Process safety issues affecting operations and maintenance are limited to cases where design choices impact system reliability. These Guidelines are intended to be applicable to the design of a new facility, as well as modification of an existing facility.

The scope excludes:

• Transportation safety
• Routine environmental control Personnel safety and industrial hygiene practices
• Emergency response
• Detailed design
• Operations and maintenance
• Security issues unrelated to process safety

These Guidelines highlight safety issues in design choices. For example, Section 7.1.1, Electrical Area Classification, covers the safe application of electrical apparatus in the process environment required for plant safety but does not address detailed design of the electrical supply or distribution system required to operate the plant.

It is clear that choices made early in design can reduce both the potential for large releases of hazardous materials and the severity of such releases, if they should occur.

1.1 ENGINEERING DESIGN FOR PROCESS SAFETY THROUGH THE LIFE CYCLE OF THE FACILITY

Engineering design for process safety must be an integral part of the life cycle of a facility. Process safety has been defined in previous publications as:

A discipline that focuses on the prevention and mitigation of fires, explosions, and accidental chemical releases at process facilities. Excludes classic worker health and safety issues involving working surfaces, ladders, protective equipment, etc. (Ref. 1–2).

Hazard evaluations are one method used to identify, evaluate, and control hazards involved in chemical processes. Hazards can be defined as characteristics of systems, processes, or plants that must be controlled to prevent occurrence of specific undesired events. Hazard evaluation is a technique that is applied repeatedly throughout the design, construction, and operation phases of a facility (Figure 1.1). Engineering design for process safety should be considered within the framework of a comprehensive process safety management program as described in Plant Guidelines for Technical Management of Chemical Process Safety (Ref. 1–3).

Figure 1.1 Identifying Hazards Through the Facility Life Cycle

Hazard evaluation is synonymous with process hazard analysis and process safety review. From conceptual design to decommissioning, no single method of hazard evaluation applies to all of the stages of a project. Different methods are required for different stages of a project, such as research and development, conceptual design, startup and operation. Table 1.1 presents some of the stages of facility life cycle and typical corresponding process hazard evaluation objectives. An objective shown for one stage may be applicable to another.

Table 1.1 Typical Hazard Evaluation Objectives at Different Stages of a Facility Life Cycle

Stage of Facility Life Cycle	Example Hazard Evaluation Objectives
Research and Development	Identify chemical interactions that could cause runaway reactions, fires, explosions, or toxic gas releases Identify process safety data needs
Conceptual Design	Identify opportunities for inherent safety Compare the hazards of potential sites
Pilot Plant	Identify ways for toxic gas to be released to the environment Identify ways to deactivate the catalyst Identify potentially hazardous operator interfaces Identify ways to minimize hazardous wastes
Engineering	Identify ways to prevent flammable mixtures inside process equipment Identify how a loss of containment might occur Identify which process control malfunctions will cause runaway reactions Identify ways to reduce hazardous material inventories Identify safety-critical equipment that must be regularly tested, inspected, or maintained Identify operating conditions that effect selection of materials of construction (e.g., corrosivity) Identify incompatibility / reactivity issues Identify relief system and discharging location impact
Construction and Startup	Identify error-likely situations in startup and operating procedures Verify that all issues from previous hazard evaluations were resolved satisfactorily and that no new issues were introduced Identify hazards that adjacent units may create for construction and maintenance workers Identify hazards associated with the vessel-cleaning procedure Identify any discrepancies between the as-built equipment and the design drawings
Routine Operation	Identify employee hazards associated with the operating procedures Identify ways an overpressure transient might occur Identify hazards associated with out-of-service equipment
Process Modification or Plant Expansion	Identify whether changing the feedstock composition will create any new hazards or make any existing hazards more severe Identify hazards associated with new equipment
Decommissioning	Identify how demolition work might affect adjacent units Identify any fire, explosion, or toxic hazards associated with the residues left in the unit after shutdown

As illustrated in Table 1.1, different types of hazards can be identified during the stages of a facility’s life cycle. Findings from the Baker Panel report (Ref. 1–4) associated with the 2005 Texas City Refinery Explosion illustrate the importance of engineering design for process safety:

Not all refining hazards are caused by the same factors or involve the same degree of potential damage. Personal or occupational safety hazards give rise to incidents—such as slips, falls, and vehicle accidents—that primarily affect one individual worker for each occurrence. Process safety hazards can give rise to major accidents involving the release of potentially dangerous materials, the release of energy (such as fires and explosions), or both. Process safety incidents can have catastrophic effects and can result in multiple injuries and fatalities, as well as substantial economic, property, and environmental damage. Process safety refinery incidents can affect workers inside the refinery and members of the public who reside nearby. Process safety in a refinery involves the prevention of leaks, spills, equipment malfunctions, over-pressures, excessive temperatures, corrosion, metal fatigue, and other similar...