Explosion Hazards in the Process Industries

Rolf K. Eckhoff

• Publisher: Gulf Professional Publishing
• Year: 2016
• eBook ISBN: 9780128032749
• Edition: 2
• Topic: Business
• Subtopic: Insurance
• Index: Business

Explosion Hazards in the Process Industries, Second Edition, delivers the most current and comprehensive content for today's process engineer. Process safety and petrochemical engineers inherently accept that there is a risk of explosions when working on process facilities such as plants and refineries. Yet many that enter this field do not have a fundamental starting point to understand the nature of explosions, and there are a lot of misconceptions and impartial information in the market. Explosion Hazards in the Process Industries, Second Edition, answers this need by providing engineers and consultants a go-to reference and training guide to understand the principles of explosions, what causes them, and how to mitigate and prevent them from reoccurring. Enhanced to include new chapters on BLEVE (Boiling Liquid Expanding Vapor Explosions), water vapor explosions, and destructive effects from accidental explosions, this guide continues to fulfill a comprehensive introduction to the subject, rounded out with new case studies, references, and a discussion on methods of hazard and risk analysis. - Eckoff, Dust Explosions in the Process Industries, 3rd Edition, 9780750676021, Jun 2003, $240.00 - Amyotte, An Introduction to Dust Explosions, 9780123970077, Jun 2013, $49.95 - Barton, Dust Explosion Prevention and Protection, 9780750675192, Mar 2002, $155.00 - Nolan, Handbook of Fire and Explosion Protection Engineering Handbook Principles, 3rd, 9780323313018, May 2014, $160.00

Chapter One

Introduction

Abstract

At the outset, this chapter emphasizes that process safety remains a persistent challenge in all process industries. The concept of “explosion” is discussed and alternative definitions presented. The most typical accidental explosions in the process industries are gas/vapor and dust explosions. However, although the two types of explosive clouds have quite similar ignition and combustion properties, there are other important differences. The influence of inertial forces on fuel particle movement are very different, and the ability of the fuel to migrate through narrow gaps in enclosure walls. Both differences greatly influence how and where accidental explosive clouds are likely to be generated in process industries. The vague, general concept of “explosive atmosphere” used in the European Union is challenged. Finally, the chapter emphasizes the importance of accounting for possible domino/escalation effects from accidental explosions, and the role of the “human” factor.

Keywords

Domino effects; Explosion hazard; Explosive atmosphere; Human factor; Process safety

1.1. Process Safety—A Persistent Challenge

Right from the start of the development of the oil and natural gas industry on the Norwegian continental shelf very high safety standards were established. This was a matter of both attitude in industry and official national policy. Until the Piper Alpha oil production platform explosion catastrophe in the North Sea in 1988, it was felt by some people that Norway was overdoing safety issues in its offshore industry. However, after this accident, the imposition of strict safety requirements in offshore oil and gas industries gained wide international acceptance. The more recent blowout, explosion, and fire catastrophe on the oil platform Deepwater Horizon in the Gulf of Mexico in 2010 has undoubtedly amplified this trend. It has also been pointed out that substantial benefits would result if the high standards of safety in the offshore industries could be adapted to industry onshore and to society at large.

However, high safety levels cannot be established once and for all by a single all-out effort. Deterioration results if the high level once attained is not actively secured by continuous maintenance and renewal. This applies to both safety technology and human factors.

Education has a key role in the continuous maintenance and renewal process. This ranges from short practical training courses to in-depth long-term education. Universities and colleges have responded to the challenge by establishing courses of study on a wide range of safety aspects. In the case of process safety, relevant topics include reliability and risk analysis; the physics, chemistry, and technology of processes and hazards; and means of accident prevention and mitigation. Much emphasis has been put on methods of reliability and risk analysis, which are indeed very important. However, it is sometimes felt by the process industry itself that education in the “hard” aspects, ie, the physics, chemistry, and technology of processes and process hazards, has been somewhat left behind. This situation presents a special challenge to universities and colleges. In 1996 the University of Bergen established a course of study in process safety technology, with particular emphasis on the scientific and technological aspects.

In process safety, the prevention of fires and explosions, and the mitigation of their effects, is a central concern. In the case of combustible gases/vapors, loss of confinement of the combustible substance is the first step in the accidental chain of events. The next steps are generation and ignition of the flammable cloud, resulting in explosion and/or fire, which may in turn cause loss of life and limb, and damaged process plant, adjacent process areas, and even more remote building structures. As pointed out in Section 1.6 below, understanding the processes of accident escalation is an important aspect of process safety technology.

Quantitative risk analysis plays an increasing role in the effort to improve offshore process safety. In the offshore oil and gas industries highly packed, congested process plants, with compact living quarters as close neighbors, ask for very systematic and thorough analysis of all possible risk factors, including the human elements. A concise and constructive official authority policy constitutes an important basis for ensuring the necessary high level of safety.

This book has been written with intent to be a useful source of basic information on the origin, course, prevention, and mitigation of accidental explosions in the process industries. Potential readers/users of the book are expected to include people both from a wide range of process industries, from official authorities, from engineering companies, and not least the students in technical colleges and universities.

1.2. What Is an Explosion?

The concept of explosion is not unambiguous. Various encyclopedias give varying definitions that mainly fall into two categories. The first focuses on the noise or “bang” due to the sudden release of a strong pressure wave, or blast, into the ambient atmosphere. The origin of this pressure wave, whether a chemical or mechanical energy release, is then of secondary concern. This definition of an explosion is in accordance with the basic meaning of the word (“sudden outburst”).

The second main category of explosion definitions is confined a sudden release of chemical energy as heat. This includes explosions of gases, dust clouds, and solid explosives. The emphasis is then put on the chemical energy release itself, and an explosion is defined accordingly. One possible definition could then be “An explosion is an exothermal chemical process that, when occurring at constant volume, gives rise to a sudden and significant pressure rise.”

In the present book, the definition of an explosion will shift pragmatically between the two alternatives, by focusing at either cause or effect, depending on the context. It should be noted that genuine, physical water vapor explosions (see Chapter 4) require a separate definition, because in these explosions the driving force is physical heat transfer, not exothermal chemical reaction.

1.3. Gas/Vapor and Dust Explosions—Real Hazards in the Process Industries

In the present book, the two largest chapters are devoted to gas/vapor explosions and dust explosions. This is justified by the fact that these two accidental explosion categories seem to represent the majority of accidental explosions in the process industries. The particular industries/facilities in which gas/vapor or dust explosion hazards may exist include:

Oil and natural gas industries/activities

• Oil and natural gas production installations on- and offshore

• Oil and gas refineries

• Systems for transportation of oil and gas (pipelines, ships, trains, cars, etc.)

Petrochemical, chemical, and metallurgical process industries

• Petrochemical industries producing chemicals and polymers

• Plants producing pharmaceuticals, pesticides, organic pigments, etc.

• Paint-production plants

• Pulverized-metal production (aluminum, magnesium, silicon, silicon alloys, etc.)

• Chemical food and feed production

• Production of cellulose, paper, etc., from wood

Mechanical processing

• Grain and feed storage

• Flour mills

• Sugar refineries

• Mechanical wood refining (hardboard, etc.)

Special processes

• Production, storage, and handling of explosives, pyrotechnics, and propellants

1.4. How and Where Accidental Explosive Gas/Vapor and Dust Clouds Are Generated in the Process Industries: Basic Differences

1.4.1. Similar Ignition and Combustion Properties of Clouds Generated

Before discussing the obvious basic differences in the modes of generation of explosive gas/vapor clouds and dust clouds, a possible reason for the similarity should be mentioned. As pointed out by Eckhoff (2006, 2009), explosive gas mixtures and explosive clouds of mists/sprays and dusts, once existing, exhibit very similar ignition and combustion properties, such as:

• flammability/explosibility limits

• laminar burning velocities and quenching distances

• the response of the burning velocity to cloud turbulence

• detonation phenomena

• adiabatic constant-volume explosion pressures of similar magnitudes

• well-defined minimum ignition energies, and

• minimum ignition temperatures for given experimental conditions

Recognition of these similarities may have contributed to the idea that the hazards of accidental gas/vapor and dust explosions could be regarded essentially identical. However, as discussed in Section 1.4.3 (in the following), this idea is only partly correct. One basic difference between gases/vapors and dusts is in the ranges of hazardous fuel concentrations. For combustible gas/vapor clouds, flame propagation is only possible when the fuel/air mixing ratios lie between the lower and the upper flammability limits. However, in the case of dusts, flame propagation is not limited only to the flammable dust concentration range of clouds. Settled dust as layers/deposits presents an additional singular regime of flame propagation. This is because, contrary to combustible gases/vapors, settled dusts are porous and will trap air in the voids between the particles. This makes it possible for sustained, although often very slow, combustion to propagate throughout such deposits.

1.4.2. Influence of Inertial Forces on the Movement of Dust Particles in a Dust Cloud

Once a combustible gas has been homogeneously mixed with air, the mixture will tend to stay homogeneous due to random molecular motion. In clouds of dust particles, however, the fuel particles are generally so much larger than the molecules of the air (often in the range 1–100 μm) that their movement within the air is controlled by inertial forces, including gravity, rather than by random molecular motion. The role of inertial forces increases systematically with increasing particle size and increasing density of the particle material. Turbulence and other convective movement of the air can prolong the time over which the particles will stay in suspension.

1.4.3. Fundamental Differences Between the Ways Explosive Clouds Are Generated

The fundamental differences between explosive clouds of gases/vapors and dust clouds are in the ways and circumstances in which clouds of the two fuel categories are generated and sustained. The basic physics of generation and sustainment of airborne clouds of dusts and of premixed clouds in air of gas/vapor are substantially different. These differences have a major impact on the choice of means by which accidental explosions are prevented and mitigated. The ...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Dedication
• About the Author
• Preface to First Edition
• Preface to Second Edition
• Chapter One. Introduction
• Chapter Two. Gas and Vapor Cloud Explosions
• Chapter Three. Boiling Liquid Expanding Vapor Explosions (BLEVEs)
• Chapter Four. Water-Vapor Explosions
• Chapter Five. Explosions of Clouds of Combustible Liquid Droplets in Air
• Chapter Six. Gas and Dust Explosions Caused by Smoldering Combustion in Powder Layers and Deposits
• Chapter Seven. Dust Explosions
• Chapter Eight. Explosives, Pyrotechnics, and Propellants
• Chapter Nine. Destructive and Harmful Effects by Pressure, Solid Fragments, and Heat From Accidental Explosions
• Chapter Ten. Design of Electrical Apparatuses for Hazardous Areas
• Chapter Eleven. Review of Some Methods of Hazard and Risk Analysis
• References
• Index