Development and Control of Dust Explosions

John Nagy

• Publisher: CRC Press
• Year: 2017
• ISBN:
  9781351455596
• Edition: 1
• Topic: Tecnología e ingeniería
• Subtopic: Ingeniería civil

In all the diverse industries-from food and agriculture to plastics- where combustibledust exists, the possibility of an explosion looms as an ever-present threat. Gathering awealth of practical, theoretical, and experimental data, this important work provides a'state-of-the-art study of the Development and Control of Dust Explosions, promotingimproved control over such hazards.Comprehensive in scope, this single-source reference presents invaluable guidelines for awide variety of planning and operational activities, including calcu lation of explosionpressure and vent area required to minimize explosion damage... the development ofmathematical mode ls used in the evaluation of explosion phenomena... determinationof the effect of numerous factors on explosion development... and control and preventionof the ignition of dust by eliminating the fines in a product.With this outstanding book, industrial, safety, mechanical, manufacturing, loss prevention, fire protection, and chemical engineers; as well as plant managers, operators, anddesigners; and all other specialists concerned with the possibility of dust exp losions nowhave an authoritative reference. The book also serves as the basis for further research inthis important field. In addition, the unique range of data included makes th is volumeideal for in-house training programs, professional seminars, and college-level coursesstudying explosion safety and safety engineering.

Chapter 1

Introduction

Scope

This book presents a comprehensive treatment of the development and control of dust and gas explosions. 11 was originally intended to address dust explosions alone, but since gas and dust explosion development is similar, some facets of gas explosions are considered. The work is an outgrowth of the research conducted primarily from 1940 through 1970 by the Dust Explosions Section of the U.S. Bureau of Mines. A complete list of the Bureau's studies conducted by the Dust Explosions Section is included in the references to this chapter. These references deal mostly with factors affecting dust explosibility. This book consolidates these research reports and extends the work with particular reference to explosions in closed and vented vessels.

Explosions in Industry

Precise statistical data on the number of explosions and the resulting injuries and fatalities occurring in the United States cannot be given because explosion incidents are not mandated to be reported to any agency. The gas explosion hazard is more prevalent than the dust explosion hazard because of the wide use of a variety of combustible gases in industry, and because natural gas is widely used in homes.

The first well-documented dust explosion incident occurred in an Italian flour mill in 1785. Dust explosions continue to occur in a wide variety of industries. During the period from 1970 to 1980, about 100 reportable industrial dust explosions occurred, causing approximately 25 fatalities. The average yearly property loss was about $20 million. This estimate does not include losses from grain dust explosions. According to U.S. Department of Labor statistics, 250 grain dust explosions occurred during the period from 1958 to 1978 causing 164 fatalities. In 1977, there were 21 grain dust explosions which caused 65 fatalities. The property loss in these explosions exceeded $500 million. The potential explosion hazard of grain dusts does not differ from that of other combustible dusts. Generally, the magnitude of the operations involved in the storage and transfer of agricultural dusts is greater than for other types of dust.

In his recent book on explosion, Bartknecht [44] states that in Europe more than 4000 dust explosions occurred in the past 12 years. This amounts to about one explosion each working day. His data were obtained from insurance records and are more complete and reliable than the preceding estimates made for American industry. It is surmised that the number of explosions in American industry are comparable to those in Europe.

The hazard of a gas or dust explosion encompasses all segments of American industry, no matter what type of combustible gases or dusts are present. The gases or dusts may be the main or intermediate product or by-products. Some of the more common materials presenting a dust explosion hazard are drugs, dyes, feeds, fertilizers, foods, grain, insecticides, meals, metals, paper, plastics, rubber, sulfur, soaps, spices, starches, wood, and of course, those plants using coal or other carbonaceous materials. Explosions have occurred in buildings from dust on the floor, on ledges, and on beams. They have also occurred in ducts, pipes, and in equipment such as bins, blenders, buffers, coating machines, collectors, conveyors, crushers, driers, elevators, furnaces, grinders, machinery, mixers, ovens, packaging, pneumatic transport, pulverizers, screens, silos, spreaders, and storage facilities. A potential dust explosion hazard is intensified by the presence and multiplicity of potential igniting sources.

Research on Explosions

Industrial Explosions

Research on the explosion hazard of gases and dusts is actively pursued by industrial organizations, universities, private laboratories, insurance groups, and by State and Federal agencies. Much of the research overlaps studies on fires. Efforts paralleling those in the United States are made in most industrialized and coal mining countries. Although the potential explosion hazards of gases were recognized for centuries, general recognition of the hazards from dusts began at about the turn of the 20th Century. Recognition of explosion and fire hazards in an organized manner began formally in the United States with the National Fire Protection Association. The National Fire Protection Association was organized in 1896 to promote the science, improve methods of fire protection and prevention, obtain and circulate information on these subjects, and secure the cooperation of its members in establishing proper safeguards against loss of life and property. In 1922, the NFPA formed a Committee on dust explosion hazards. This Committee has remained active and has coordinated results of research efforts from government, industry, and academia to provide industry with effective codes for minimizing hazards and preventing explosions. Shortly thereafter, the Association began to publish specific codes [45] for the control of gas and dust hazards. This organization has consistently devoted much energy and time to education, publicizing the hazards, and developing codes for safe operations in industry and homes.

Shortly after the turn of the present century, the Department of Agriculture and the Department of the Interior began explosibility studies on industrial and grain dusts. In the mid-1930's, governmental activities became restricted as a result of the depression and these two organizations ceased their experimentation. In 1910, the Bureau of Mines began to study the causes of and to develop means to minimize disasters in coal mines. Much of the research on mine explosions was conducted in the Experimental Coal Mine at Bruceton, Pennsylvania. Associated with the large-scale studies in the mine were laboratory and surface-testing facilities. These facilities were used to a limited extent to study the hazards of gases and dust in industrial and other operations. The Bureau's work on industrial explosions increased in 1936 and during the 1940's supportive research was performed for the military. Following World War II, research by the Bureau of Mines on industrial dusts became broader in scope to include many of the dusts commonly found in American industry and to begin a study of venting. The work by the Bureau of Mines on industrial dusts continued until 1970 when this phase was curtailed following the passage of the Coal Mine Health and Safety Act of 1969. Emphasis was then given primarily to the study of mining hazards, mineral dust explosions, and the promulgation of mine health and safety regulations.

In the development of equipment and test procedures for evaluating dust explosion parameters, those engaged in applied research tend to use physical test arrangements which produce values representing the maximum hazard. Most industrial explosions are less severe than the maximum; however, in some instances, the most violent type of explosion does occur in industry. As such circumstances do exist in industry, the engineer or others responsible for plant safety must, therefore, choose the degree of protection that can be afforded and yet be consistent with the potential hazards present. Gross estimation usually must be made of several of the variables, particularly for vent area calculations.

The engineer designing a vessel or structure in which a gas and/or a dust explosion may occur has a formidable task. In designing for containment, one must consider the vessel size and strength; the type and concentration of fuel; the initial temperature and pressure; turbulence; the intensity and location of the ignition source; uniformity and extent of mixture; and also make judgment as to the factor of safety. For venting, one must consider all these factors, as well as the vessel shape, initial turbulence, potential location of igniting source relative to the vent, and the type of vent closure. A long, narrow container may require several vents, but a single vent may suffice for a spherical or cubical container. The factor of initial turbulence does not materially affect the maximum pressure developed in a closed vessel, but does significantly affect pressure development in a vented vessel. For a vented vessel, the location and intensity of the igniting source may affect the rate of explosion development by a factor as high as 8, and the maximum pressure by a factor of 4, depending on the shape and size of the container. Finally, the engineer must consider the size, shape, and location of the vents, together with the type and bursting strength of the vent closure. For both vented and unvented explosions, the type of fuel (its fundamental reaction rate), the oxygen content of the atmosphere, and the presence of inert material are prime factors. For dusts, the shape and particle size are major concerns.

Mine Explosions

Mine passageways provide a significantly greater degree of confinement to an explosion than do buildings on the surface. Hence, a mine explosion generates highly destructive wind forces from the dynamic pressure which develops. In a mine, these forces cause damage at great distances from the origin of the explosion. Explosions in surface industries are usually considered separately from those in underground mines, partly because of the different environment, and partly because methane gas is usually involved in the mine explosions. An overview of the explosion hazard in mines which summarizes current knowledge was recently published [46]. In surface explosions, the destructive forces are generally confined to the area exposed to the high static pressure generated by the explosion. The destructive forces may result from a primary or from a secondary dust explosion.

Related Explosion Hazards

Although dust, gas, and mist explosions are possible with gases other than oxygen (e.g., chlorine), their occurrence in industry is relatively rare. For this reason, the ensuing treatment considers the oxidation reaction.

No attention in this book is given to the explosion hazard of combustible mists or of the hazards of primary explosives.

Reference Material

Much work has been performed in the field of gas and dust explosions. Pertinent references are included to support observations or conclusions; however, no attempt is made to provide a complete bibliography in this text. Much of the laboratory data obtained by the Bureau of Mines have been republished in tabular form in the NFPA Fire Protection Handbook [47]. Similar data were published by the Germans [48] for more than 800 dusts. Explosibility data were also published by the British [49] in 1968. A study on the ignition and explosion characteristics of gases was published by the Bureau of Mines in 1965 [50].

The subject of the venting of explosions is being studied universally. H. R. Maisey [51] has provided a bibliography of the work up to 1965. Recent works on dust explosions and venting are those by Bartknecht [44], Bodurtha [52], and Field [53]. In 1973, Palmer [54] published a book on ...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright
• Dedication
• Preface
• Table of Contents
• 1. Introduction
• 2. Test Methods, Definitions, and Units of Measurements
• 3. Comparison of Dust and Gas Explosions
• 4. Ignition of Dusts
• 5. Explosion Development in a Closed Vessel
• 6. Venting Principles for Unrestricted Vents
• 7. Explosion Experiments with Unrestricted Vents
• 8. Vent Closures and Ducts
• 9. Explosion Prevention
• Index