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This book is on in a series of process safety guidelines and concept books published by the Center for Chemical Process Safety (CCPS). Please go to for a full list of titles in this series.

Introduction to
Process Safety for Undergraduates
and Engineers

of the
New York, NY

Wiley Logo


ACC American Chemistry Council
AIChE American Institute of Chemical Engineers
API American Petroleum Institute
ASME American Society of Mechanical Engineers
BLEVE Boiling Liquid Expanding Vapor Explosion
BMS Burner Management System
CEI Chemical Exposure Index (Dow Chemical)
CFR Code of Federal Registry
CMA Chemical Manufacturers Association
CSB US Chemical Safety and Hazard Investigation Board
CCPS Center for Chemical Process Safety
CCR Continuous Catalyst Regeneration
COO Conduct of Operations
CPI Chemical Process Industries
DCU Delayed Coker Unit
DDT Deflagration to Detonation Transition
DIERS Design Institute for Emergency Relief Systems
ERS Emergency Relief System
EPA US Environmental Protection Agency
FCCU Fluidized Catalytic Cracking Unit
F&EI Fire and Explosion Index (Dow Chemical)
FMEA Failure Modes and Effect Analysis
HAZMAT Hazardous Materials
HAZOP Hazard and Operability Study
HIRA Hazard Identification and Risk Analysis
HTHA High Temperature Hydrogen Attack
HSE Health & Safety Executive (UK)
I&E Instrument and Electrical
IDLH Immediately Dangerous to Life and Health
ISD Inherently Safer Design
ISO International Organization for Standardization
ISOM Isomerization Unit
ITPM Inspection Testing and Preventive Maintenance
LFL Lower Flammable Limit
LNG Liquefied Natural Gas
LOPA Layer of Protection Analysis
LOTO Lock Out Tag Out
LPG Liquefied Petroleum Gas
MAWP Maximum Allowable Working Pressure
MCC Motor Control Center
MIE Minimum Ignition Energy
MOC Management of Change
MOOC Management of Organizational Change
MSDS Material Safety Data Sheet
NASA National Aeronautics and Space Administration
NDT Non Destructive Testing
NFPA National Fire Protection Association
OCM Organizational Change Management
OIMS Operational Integrity Management System (ExxonMobil)
OSHA US Occupational Safety and Health Administration
PHA Process Hazard Analysis
PLC Programmable Logic Controller
PRA Probabilistic Risk Assessment
PRD Pressure Relief Device
PRV Pressure Relief Valve
PSB Process Safety Beacon
PSE Process Safety Event
PSI Process Safety Information
PSI Process Safety Incident
PSM Process Safety Management
PSO Process Safety Officer
PSSR Pre-Startup Safety Review
QRA Quantitative Risk Analysis
RBPS Risk Based Process Safety
RAGAGEP Recognized and Generally Accepted Good Engineering Practice
RMP Risk Management Plan
SACHE Safety and Chemical Engineering Education
SCAI Safety Controls Alarms and Interlocks
SHESafety, Health and Environmental (sometimes written as EHS or HSE)
SHIB Safety Hazard Information Bulletin
SIS Safety Instrumented Systems
SME Subject Matter Expert
TQ Threshold Quantity
UFL Upper Flammable Limit
UK United Kingdom
US United States
UST Underground Storage Tank


Asset integrityA PSM program element involving work activities that help ensure that equipment is properly designed, installed in accordance with specifications, and remains fit for purpose over its life cycle. Also called asset integrity and reliability.
Atmospheric Storage TankA storage tank designed to operate at any pressure between ambient pressure and 0.5 psig (3.45kPa gage).
Boiling-Liquid-Expanding-Vapor Explosion (BLEVE)A type of rapid phase transition in which a liquid contained above its atmospheric boiling point is rapidly depressurized, causing a nearly instantaneous transition from liquid to vapor with a corresponding energy release. A BLEVE of flammable material is often accompanied by a large aerosol fireball, since an external fire impinging on the vapor space of a pressure vessel is a common cause. However, it is not necessary for the liquid to be flammable to have a BLEVE occur.
Checklist AnalysisA hazard evaluation procedure using one or more pre-prepared lists of process safety considerations to prompt team discussions of whether the existing safeguards are adequate.
Chemical Process IndustryThe phrase is used loosely to include facilities which manufacture, handle and use chemicals.
Combustible DustAny finely divided solid material that is 420 microns or smaller in diameter (material passing through a U.S. No. 40 standard sieve) and presents a fire or explosion hazard when dispersed and ignited in air or other gaseous oxidizer.
Conduct of Operations (COO)The embodiment of an organization’s values and principles in management systems that are developed, implemented, and maintained to (1) structure operational tasks in a manner consistent with the organization's risk tolerance, (2) ensure that every task is performed deliberately and correctly, and (3) minimize variations in performance.
ExplosionA release of energy that causes a pressure discontinuity or blast wave.
Failure Mode and Effects AnalysisA hazard identification technique in which all known failure modes of components or features of a system are considered in turn, and undesired outcomes are noted.
Flammable LiquidsAny liquid that has a closed-cup flash point below 100 °F (37.8°C), as determined by the test procedures described in NFPA 30 and a Reid vapor pressure not exceeding 40 psia (2068.6 mm Hg) at 100°F (37.8 °C), as determined by ASTM D 323, Standard Method of Test for Vapor Pressure of Petroleum Products (Reid Method). Class IA liquids shall include those liquids that have flash points below 73 °F (22.8°C) and boiling points below 100 F (37.8 °C). Class IB liquids shall include those liquids that have flash points below 73°F (22.8°C) and boiling points at or above 100 °F (37.8 °C). Class IC liquids shall include those liquids that have flash points at or above 73 °F (22.8 °C), but below 100 °F (37.8 °C). (NFPA 30).
Hazard AnalysisThe identification of undesired events that lead to the materialization of a hazard, the analysis of the mechanisms by which these undesired events could occur and usually the estimation of the consequences.
Hazard and Operability Study (HAZOP)A systematic qualitative technique to identify process hazards and potential operating problems using a series of guide words to study process deviations. A HAZOP is used to question every part of a process to discover what deviations from the intention of the design can occur and what their causes and consequences may be. This is done systematically by applying suitable guide words. This is a systematic detailed review technique, for both batch and continuous plants, which can be applied to new or existing processes to identify hazards
Hazard IdentificationThe inventorying of material, system, process and plant characteristics that can produce undesirable consequences through the occurrence of an incident.
Hazard Identification and Risk Analysis (HIRA)A collective term that encompasses all activities involved in identifying hazards and evaluating risk at facilities, throughout their life cycle, to make certain that risks to employees, the public, or the environment are consistently controlled within the organization's risk tolerance.
Hot WorkAny operation that uses flames or can produce sparks (e.g., welding).
IncidentAn event, or series of events, resulting in one or more undesirable consequences, such as harm to people, damage to the environment, or asset/business losses. Such events include fires, explosions, releases of toxic or otherwise harmful substances, and so forth.
Incident InvestigationA systematic approach for determining the causes of an incident and developing recommendations that address the causes to help prevent or mitigate future incidents. See also Root cause analysis and Apparent cause analysis.
InterlockA protective response which is initiated by an out-of-limit process condition. Instrument which will not allow one part of a process to function unless another part is functioning. A device such as a switch that prevents a piece of equipment from operating when a hazard exists. To join two parts together in such a way that they remain rigidly attached to each other solely by physical interference. A device to prove the physical state of a required condition and to furnish that proof to the primary safety control circuit.
Layer of Protection Analysis (LOPA)An approach that analyzes one incident scenario (cause-consequence pair) at a time, using predefined values for the initiating event frequency, independent protection layer failure probabilities, and consequence severity, in order to compare a scenario risk estimate to risk criteria for determining where additional risk reduction or more detailed analysis is needed. Scenarios are identified elsewhere, typically using a scenario-based hazard evaluation procedure such as a HAZOP Study.
Lockout/TagoutA safe work practice in which energy sources are positively blocked away from a segment of a process with a locking mechanism and visibly tagged as such to help ensure worker safety during maintenance and some operations tasks.
Management of Change (MOC)A system to identify, review and approve all modifications to equipment, procedures, raw materials and processing conditions, other than “replacement in kind,” prior to implementation.
Management SystemA formally established set of activities designed to produce specific results in a consistent manner on a sustainable basis.
Mechanical IntegrityA management system focused on ensuring that equipment is designed, installed, and maintained to perform the desired function.
Near-MissAn unplanned sequence of events that could have caused harm or loss if conditions were different or were allowed to progress, but actually did not.
Operating ProceduresWritten, step-by-step instructions and information necessary to operate equipment, compiled in one document including operating instructions, process descriptions, operating limits, chemical hazards, and safety equipment requirements.
Operational Discipline (OD)The performance of all tasks correctly every time; Good OD results in performing the task the right way every time. Individuals demonstrate their commitment to process safety through OD. OD refers to the day-to-day activities carried out by all personnel. OD is the execution of the COO system by individuals within the organization.
Operational ReadinessA PSM program element associated with efforts to ensure that a process is ready for start-up/restart. This element applies to a variety of restart situations, ranging from restart after a brief maintenance outage to restart of a process that has been mothballed for several years.
Organizational ChangeAny change in position or responsibility within an organization or any change to an organizational policy or procedure that affects process safety.
Organizational Change Management (OCM)A method of examining proposed changes in the structure or organization of a company (or unit thereof) to determine whether they may pose a threat to employee or contractor health and safety, the environment, or the surrounding populace.
OSHA Process Safety Management (OSHA PSM)A U.S. regulatory standard that requires use of a 14-element management system to help prevent or mitigate the effects of catastrophic releases of chemicals or energy from processes covered by the regulations 49 CFR 1910.119.
Pressure Relief Valve (PRV)A pressure relief device which is designed to reclose and prevent the further flow of fluid after normal conditions have been restored.
Pressure Safety Valve (PSV)See Pressure Relief Valve
Pre-Startup Safety Review (PSSR)A systematic and thorough check of a process prior to the introduction of a highly hazardous chemical to a process. The PSSR must confirm the following: Construction and equipment are in accordance with design specifications; Safety, operating, maintenance, and emergency procedures are in place and are adequate; A process hazard analysis has been performed for new facilities and recommendations and have been resolved or implemented before startup, and modified facilities meet the management of change requirements; and training of each employee involved in operating a process has been completed.
Preventive MaintenanceMaintenance that seeks to reduce the frequency and severity of unplanned shutdowns by establishing a fixed schedule of routine inspection and repairs.
Probabilistic Risk Assessment (PRA)A commonly used term in the nuclear industry to describe the quantitative evaluation of risk using probability theory.
Process Hazard Analysis (PHA)An organized effort to identify and evaluate hazards associated with processes and operations to enable their control. This review normally involves the use of qualitative techniques to identify and assess the significance of hazards. Conclusions and appropriate recommendations are developed. Occasionally, quantitative methods are used to help prioritize risk reduction.
Process Knowledge ManagementA Process Safety Management (PSM) program element that includes work activities to gather, organize, maintain, and provide information to other PSM program elements. Process safety knowledge primarily consists of written documents such as hazard information, process technology information, and equipment-specific information. Process safety knowledge is the product of this PSM element.
Process Safety CultureThe common set of values, behaviors, and norms at all levels in a facility or in the wider organization that affect process safety.
Process Safety Incident/EventAn event that is potentially catastrophic, i.e., an event involving the release/loss of containment of hazardous materials that can result in large-scale health and environmental consequences.
Process Safety Information (PSI)Physical, chemical, and toxicological information related to the chemicals, process, and equipment. It is used to document the configuration of a process, its characteristics, its limitations, and as data for process hazard analyses.
Process Safety Management (PSM)A management system that is focused on prevention of, preparedness for, mitigation of, response to, and restoration from catastrophic releases of chemicals or energy from a process associated with a facility.
Process Safety Management SystemsComprehensive sets of policies, procedures, and practices designed to ensure that barriers to episodic incidents are in place, in use, and effective.
Reactive ChemicalA substance that can pose a chemical reactivity hazard by readily oxidizing in air without an ignition source (spontaneously combustible or peroxide forming), initiating or promoting combustion in other materials (oxidizer), reacting with water, or self-reacting (polymerizing, decomposing or rearranging). Initiation of the reaction can be spontaneous, by energy input such as thermal or mechanical energy, or by catalytic action increasing the reaction rate.
Recognized and Generally Accepted Good Engineering Practice (RAGAGEP)A term originally used by OSHA, stems from the selection and application of appropriate engineering, operating, and maintenance knowledge when designing, operating and maintaining chemical facilities with the purpose of ensuring safety and preventing process safety incidents.
It involves the application of engineering, operating or maintenance activities derived from engineering knowledge and industry experience based upon the evaluation and analyses of appropriate internal and external standards, applicable codes, technical reports, guidance, or recommended practices or documents of a similar nature. RAGAGEP can be derived from singular or multiple sources and will vary based upon individual facility processes, materials, service, and other engineering considerations.
Responsible Care©An initiative implemented by the Chemical Manufacturers Association (CMA) in 1988 to assist in leading chemical processing industry companies in ethical ways that increasingly benefit society, the economy and the environment while adhering to ten key principles.
Risk Management Program (RMP) RuleEPA’s accidental release prevention Rule, which requires covered facilities to prepare, submit, and implement a risk management plan.
Risk-Based Process Safety (RBPS)The Center for Chemical Process Safety’s (CCPS) PSM system approach that uses risk-based strategies and implementation tactics that are commensurate with the risk-based need for process safety activities, availability of resources, and existing process safety culture to design, correct, and improve process safety management activities.
Safety Instrumented System (SIS)The instrumentation, controls, and interlocks provided for safe operation of the process.
Vapor Cloud Explosion (VCE)The explosion resulting from the ignition of a cloud of flammable vapor, gas, or mist in which flame speeds accelerate to sufficiently high velocities to produce significant overpressure.


The American Institute of Chemical Engineers (AIChE) and the Center for Chemical Process Safety (CCPS) express their appreciation and gratitude to all members of the Introduction to Process Safety for Undergraduates and Engineers and their CCPS member companies for their generous support and technical contributions in the preparation of this book.

Subcommittee Members:

Don AbrahamsonCCPS - Emeritus
Iclal AtayNew Jersey DEP
Brooke CailleteauLyondellBasell (Houston Refining)
Dan CrowlMichigan Technical University
Jerry ForestCelanese - Project Chair
Robert ForestUniversity of Delaware
Jeff FoxDow Corning
Mikelle MooreBuckman North America
Albert NessCCPS – Process Safety Writer
Eric PetersonMMI Engineering
Robin PitbladoDNV GL
Dan SlivaCCPS - Staff Consultant
Rob SmithSiemens Consulting
Scott WallaceOlin Corporation

The collective industrial experience and know-how of the subcommittee members plus these individuals makes this book especially valuable to engineers who develop and manage process safety programs and management systems, including the identification of the competencies needed to create and maintain these systems.

The book committee wishes to express their appreciation to Albert Ness and of CCPS and Arthur Baulch of the AIChE for their contributions in preparing this book for publication.

Before publication, all CCPS books are subjected to a thorough peer review process. CCPS gratefully acknowledges the thoughtful comments and suggestions of the peer reviewers. Their work enhanced the accuracy and clarity of these guidelines.

Peer Reviewers:

John AldermanHazard and Risk Analysis, LLC
Dan CrowlProfessor of Chemical Engineering, Michigan Technical University, Retired
Dr. Kerry M. DooleyBASF Professor of Chemical Engineering, Louisiana State University
John HerberCCPS Staff Consultant
Greg HounsellCCPS Staff Consultant
Robert W. JohnsonPresident, Unwin Company
Jerry JonesCCPS Staff Consultant
Michael L. LaFondEngineer, Hemlock Semiconductor/Dow Corning
Robert J. LovelettChemical Engineering Student, University of Delaware
John MurphyCCPS Staff Consultant
Eloise RocheDow Chemical
Robert RosenRRS Engineering
Chad SchaefferChemical Engineering Student, University of Delaware
Steve SelkDepartment of Homeland Security
Chris TagoeVP HES, Cameron
Bruce VaughenPrincipal Consultant, BakerRisk
Ron WileyProfessor of Chemical Engineering, Northeastern University
John ZondloProfessor of Chemical Engineering, West Virginia University
Lucy YiCCPS – China Section

Although the peer reviewers have provided many constructive comments and suggestions, they were not asked to endorse this book and were not shown the final manuscript before its release.


The Center for Chemical Process Safety (CCPS) was created by the AIChE in 1985 after the chemical disasters in Mexico City, Mexico, and Bhopal, India. The CCPS is chartered to develop and disseminate technical information for use in the prevention of major chemical accidents. The Center is supported by more than 180 chemical process industries (CPI) sponsors who provide the necessary funding and professional guidance to its technical committees. The major product of CCPS activities has been a series of guidelines to assist those implementing various elements of a process safety and risk management system. This book is part of that series.

The AIChE has been closely involved with process safety and loss control issues in the chemical and allied industries for more than five decades. Through its strong ties with process designers, constructors, operators, safety professionals, and members of academia, AIChE has enhanced communications and fostered continuous improvement of the industry’s high safety standards. AIChE publications and symposia have become information resources for those devoted to process safety and environmental protection.

The integration of process safety into the engineering curricula is an ongoing goal of the CCPS. To this end, CCPS created the Safety and Chemical Engineering Education (SACHE) committee which develops training modules for process safety. One textbook covering the technical aspects of process safety for students already exists; however, there is no textbook covering the concepts of process safety management and the need for process safety for students. The CCPS Technical Steering Committee initiated the creation of this book to assist colleges and universities in meeting this challenge and to aid Chemical Engineering programs in meeting recent accreditation requirements for including process safety into the chemical engineering curricula.


1.1 Purpose of this Handbook

This book is intended to be used as a reference material for either a stand-alone process safety course or as supplemental material for existing curricula. This book is not a technical book; rather, the intent of the material is to familiarize the student or an engineer new to process safety with:

1.2 Target Audience

This primary audience for this publication is junior to graduate level Chemical Engineering students and those entering the workforce and engineers new to process safety. However, since there are no technical pre-requisites recommended, it may also be used by other engineering disciplines at similar levels.

1.3 Process Safety - What Is It?

In the chemical, petrochemical and most other industries, you will find that all companies are required to have an occupational safety program, with a focus on personal safety (this program may be required by regulations in many countries, states and local areas. It can apply to workers in a manufacturing plant, a research laboratory or pilot plant, and even to office locations). That program is going to focus on personal safety. The focus of these programs is to prevent harm to workers from workplace accidents such as falls, cuts, sprains and strains, being struck by objects, repetitive motion injuries, and so on. They are good and in fact, very necessary programs. They are not, however, what Process Safety is about.

Process Safety is defined as “a discipline that focuses on the prevention of fires, explosions, and accidental chemical releases at chemical process facilities”. Such events don't only happen at chemical facilities, they occur in refineries, offshore drilling facilities, etc. Another definition is that process safety is about the prevention of, preparedness for, mitigation of, response to, or restoration from catastrophic releases of chemicals or energy from a process associated with a facility.

After an explosion in a BP Texas City refinery in 2005 that killed 15 people and injured over 170 others, an independent commission was created to examine the process safety mind-set, or culture, of BPs refinery operations, this commission came to be known as the Baker Panel. The Baker Panel said this about process safety:

“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 conditions. Process safety programs focus on the design and engineering of facilities, hazard assessments, management of change, inspection, testing, and maintenance of equipment, effective alarms, effective process control, procedures, training of personnel, and human factors.” (Ref 1.1)

The term “refinery” in that paragraph can be replaced by “petrochemical plant”, “chemical process facility”, “solids handling facility”, “water treatment plants”, “ammonia refrigeration plants”, “off-shore operations” or any number of terms for a plant that handles or processes flammable, combustible, toxic, or reactive materials. For the rest of this book, the term process facility or just facility will be used to mean the previously mentioned facilities and any other operation that handles or processes flammable, combustible, toxic, or reactive materials.

The quote from the Baker report states that process safety is not limited to the operation of a facility. During the basic research and process research phases, process safety programs cover the operation of pilot facilities. They also cover the selection of the chemistry and unit operations chosen to achieve the design intent of the process. During the design and engineering phase, process safety is involved in choices about what type of unit operations and equipment items to use, the facility layout, and so on. Running a facility involves, as was mentioned above, “hazard assessments, management of change, inspection, testing, and maintenance of equipment, effective alarms, effective process control, procedures, and training of personnel”. The choices made about process features during research and development and pilot work can make these activities easier or more difficult.

1.4 Organization of the Book

Chapter 2 gives a brief history of process safety and of process safety management. The evolution of process safety management principles from the initial twelve elements of process safety management developed by CCPS, and the process regulatory framework of the Occupational Safety and Health Administration’s (OSHA) PSM regulations to the current twenty elements of the CCPS Risk Based Process Safety (RBPS) management system is discussed.

Chapter 3 describes several process safety incidents that demonstrate the need for a good PSM system. Each incident is described, and then the relevance of a few relevant RBPS elements are listed.

Chapter 4 describes the role of several engineering disciplines, Chemical, Mechanical, Civil, Instrumentation and Electrical (I&E) Engineers, and Safety Engineers with respect to how new engineers will be involved in process safety. PSM is a team effort between many disciplines.

Chapter 5 covers a few key process safety concerns with respect to some unit operations and equipment found in the chemical, biochemical and petrochemical and industries that could handle hazardous materials. Combinations of these unit operations are many and varied across the process industries. In the petrochemical industry there are several common operations that are used, and this book describes the process safety concerns of some of those operations. This chapter also introduces the concept of Inherent Safety (IS) and Inherently Safer Design (ISD). ISD focuses on eliminating or reducing hazards inherent in a process as opposed to trying to manage the hazards.

Chapter 6 lists training modules available from the Safety and Chemical Engineering Education (SACHE) Committee through the AIChE and describes the courses and their relevance to some Chemical Engineering courses. This chapter can be used as a guide for supplementing existing courses.

Chapter 7 describes process safety related duties that a new engineer can expect to encounter during the first year to two years in the process industry. For a PSM system to work well, all people involved in the process must execute their roles and responsibilities in a deliberate and structured manner to achieve a high level of human performance. This is called Conduct of Operations. Chapter 7 describes many tasks of engineers with respect to Conduct of Operations, as well as what the engineer should expect operators, maintenancde and management with respect to their roles.

1.5 References

  1. 1.1 The Report of the BP U.S. Refineries Independent Safety Review Panel, January 2007. (