Table Of ContentChapter 1
Introduction: Dust Explosions—
Myth or Reality?
An Introduction to Dust Explosions. http://dx.doi.org/10.1016/B978-0-12-397007-7.00001-X
Copyright © 2013 Elsevier Inc. All rights reserved. 1
2 An Introduction to Dust Explosions
Unicorn: a mythical animal generally depicted with…a single horn in the middle of the
forehead.
—Merriam-Webster’s Online Dictionary
There is a problem, the nature of which is not well understood, in communicat-
ing the results of dust explosion testing and research to stakeholders in industry,
government, and the public. In a recent article on dust explosions, I was quoted
as follows [1] (p. 47):
When I hear about yet another dust explosion, I hang my head. When someone who has
been in the industry for a certain number of years says that they didn’t know sugar or flour
or aluminum could explode because they’d never seen it happen before—that’s just wrong.
The answer to this problem is neither as trivial nor as obvious as it may seem.
A partial answer—or at least the idea for the paper [2] providing the basis for
this book—came from Professor Trevor Kletz during his workshop held as part
of the Hazards XXI symposium in Manchester, UK (November 2009). Profes-
sor Kletz commented that when poor or impracticable designs are examined,
some people may not question the intention of the designers, whereas others
may speak up because they see technical oversights and hazards that were not
seen before. To illustrate his point, he showed a slide of an animal with what
appeared to be a single horn in the center of its forehead (see Figure 1.1). Was it
a unicorn? No; the next slide showed the same animal (an oryx) from a different
angle, and now it was clear there were two horns on its head (see Figure 1.2).
What we see depends on the way we look [3].
So perhaps dust explosions do occur, in part, because we believe in
unicorns—in myths that lack appropriate elements of the natural, management,
and social sciences and engineering principles associated with dust explosion
prevention and mitigation. This book explores 20 such myths drawn from my
FIGURE 1.1 Unicorn? (Photograph courtesy of T. Kletz.)
Chapter | 1 Dust Explosions—Myth or Reality? 3
FIGURE 1.2 No—oryx! (Photograph courtesy of T. Kletz.)
Mixing Confinement
Fuel Oxidant
Ignition Source
FIGURE 1.3 The explosion pentagon.
research activities and experience in providing dust explosibility test results to
industry. Other practitioners and authors would undoubtedly come up with a
different set of attitudes and beliefs needing closer examination, but the ones
presented here form a useful starting point for a dialogue structured around the
explosion pentagon shown in Figure 1.3.
1.1 EXPLOSION PENTAGON
In many respects the explosion pentagon affords us everything we need to know
on a fundamental level about dust explosion causation [4]. When the require-
ments of the pentagon are satisfied, the risk of a dust explosion arises. These
requirements include the familiar need for a fuel, an oxidant, and an ignition
source, augmented by mixing of the fuel and oxidant, as well as confinement
of the resulting mixture. The first of these additional components illustrates a
4 An Introduction to Dust Explosions
key difference between dust and gas explosions—a solid rather than a gaseous
fuel. In a dust/air mixture, the dust particles are strongly influenced by grav-
ity; an essential prerequisite for a dust explosion is therefore the formation of
a dust/oxidant suspension. Once combustion of this mixture occurs, confine-
ment (partial or complete) permits an overpressure to develop, thus enabling a
fast-burning dust flame to transition to a dust explosion [5].
As helpful as the explosion pentagon may be in understanding why dust
explosions occur, it is neutral in terms of how individuals interpret, prevent,
and mitigate these requirements. The ensuing chapters illustrate connections
between the various pentagon elements and myth typified by erroneous belief
(the unicorn), as well as reality expressed through scientific and engineering
fact (the oryx). The book concludes with a set of 20 facts to counterbalance the
20 myths identified throughout.
1.2 DUST EXPLOSION MYTHS
The myths associated with dust explosions and which are explored in this book
are the following [with the applicable pentagon element(s) shown in italics]:
l Dust does not explode (fuel).
l Dust explosions happen only in coal mines and grain elevators (fuel).
l A lot of dust is needed to have an explosion (fuel).
l Gas explosions are much worse than dust explosions (fuel).
l It’s up to the testing lab to specify which particle size to test (fuel).
l Any amount of suppressant is better than none (fuel/ignition source).
l Dusts ignite only with a high-energy ignition source (ignition source).
l Only dust clouds—not dust layers—will ignite (ignition source).
l Oxygen removal must be complete to be effective (oxidant).
l Taking away the oxygen makes things safe (oxidant).
l There’s no problem if dust is not visible in the air (mixing).
l Once airborne, a dust will quickly settle out of suspension (mixing).
l Mixing is mixing; there are no degrees (mixing).
l Venting is the only/best solution to the dust explosion problem (confinement).
l Total confinement is required to have an explosion (confinement).
l Confinement means four walls, a roof, and a floor (confinement).
l The vocabulary of dust explosions is difficult to understand (pentagon).
l Dust explosion parameters are fundamental material properties (pentagon).
l It makes sense to combine explosion parameters in a single index (pentagon).
l It won’t happen to me (pentagon).
1.3 WHY THIS BOOK?
The answer to the question “Why this book?” is obtained by examining what
the current book is intended to be, and what it is not intended to be. Starting
Chapter | 1 Dust Explosions—Myth or Reality? 5
with the latter point, this book has not been written as a comprehensive treatise
on all important aspects of dust explosions. Such an endeavor would require a
different focus in reviewing the intensive research on dust explosions that has
been conducted in the public and private sectors over the past several decades.
This research has led to many advances including improved understanding
of dust explosion fundamentals [6], enhanced mitigation techniques such as
venting and suppression [7], and recognition of the role of inherently safer
design in dust explosion prevention and mitigation (Chapter 13 in Kletz and
Amyotte [8]).
The preceding text references are available to readers who desire advanced
treatment in the areas indicated. Additionally, various archival journal arti-
cles have been written for specialists in industrial loss prevention and dust
explosion research. As explained by Amyotte and Eckhoff [5], recent reviews
cover in detail case histories, causes, consequences, and control of dust explo-
sions [9]; the role of powder science and technology in understanding dust
explosion phenomena [10]; and the status of developments in basic knowl-
edge and practical applications with respect to dust explosion p revention and
mitigation [11].
While the scope of the current book is also related to dust explosion phe-
nomena (specifically the prevention and mitigation of dust explosions), it differs
from the other works cited in the preceding paragraph in terms of both motiva-
tion and objective. Having said this, I would be remiss in not acknowledging the
role played by these resources in writing my own manuscript (as evidenced by
the numerous references to them throughout).
The writing of this book has been motivated in equal measure by a desire
to aid in the protection of people, business assets, operational production, and
the natural environment, and a need to address important communication issues
with respect to understanding dust explosions.
More generally, one of the process safety research topics identified in the
recently published Process Safety Research Agenda for the 21st Century [12]
is easy-to-implement process safety methods for industry. Quoting from this
document [12] (p. 42):
Due to the sophistication needed to make progress, the gap in the level of theoretical
knowledge between academia and most industry experts tends to widen and become
an obstacle to communication. This can cause a decrease both in the flow of industry
experience to academia and the implementation of newly acquired knowledge to industry.
Special effort should be made to counter this trend. Easy-to-implement methods require
the developer to fully master the method and the knowledge it is based on in order to
describe complex phenomena in simple terms and make the method transparent and user
friendly.
These motivational points have led to the objective of exploring the myths and
realities associated with dust explosion risk reduction. To achieve this objec-
tive, I have attempted to provide extensively referenced facts on dust explosions
6 An Introduction to Dust Explosions
in a manner that clearly and unambiguously refutes several misconceptions
about dust explosions. A key feature in this regard is the closing section of each
chapter in which readers are invited to express their own thoughts on questions
related to the specific content of the chapter.
1.4 WHAT DO YOU THINK?
As noted on its website (www.csb.gov), the U.S. Chemical Safety and Haz-
ard Investigation Board (Chemical Safety Board or CSB) is an independent,
non-regulatory federal agency that conducts root cause investigations of chemi-
cal accidents at fixed industrial facilities. The reports of its investigations
are available on the CSB website for downloading and are often accompa-
nied by video footage and animation of the incident sequence [8]. These
reports—incident investigations, case studies, safety bulletins, and urgent
recommendations—are an excellent resource for training exercises aimed at
learning lessons from previous incidents.
The following excerpt is taken from the CSB document describing the
results of a recent investigation effort [13] (p. 2):
This case study examines multiple iron dust flash fires and a hydrogen explosion at
the Hoeganaes facility in Gallatin, TN. The first iron dust flash fire incident killed
two workers and the second injured an employee. The third incident, a hydrogen
explosion and resulting iron dust flash fires, claimed three lives and injured two other
workers.
This particular Hoeganaes plant manufactures atomized iron powder for the
production of metal parts in the automotive and other industries. Hydrogen is
used in the plant’s continuous annealing furnaces to prevent oxidation of the
iron powder. Further details, including the answers to the following questions,
can be found in the CSB case study [13].
Before reading the full report, however, consider the following questions
based on your current knowledge and understanding of the explosion pentagon
and its various elements:
l Fuel: Can metal dusts such as iron explode? What range of iron dust particle
sizes would be expected to support an explosion?
l Ignition Source: What is a typical energy required to ignite a cloud of iron
dust particles with diameters < 75 µm? What about the temperature of a hot
surface required to ignite such a dust cloud?
l Oxidant: Is it practical to eliminate oxygen-containing air from all plant areas
in which a dust explosion might occur?
l Mixing: How could iron dust deposits such as those shown in Figure 1.4 be
raised into suspension?
l Confinement: What would be required for an iron dust flash fire to transition
to an explosion?
Chapter | 1 Dust Explosions—Myth or Reality? 7
FIGURE 1.4 Iron dust deposits on elevated surfaces at the Hoeganaes Corporation facility in
Gallatin, TN, on February 3, 2011 [13].
REFERENCES
[1] K enter P. Big bang theory. OHS Canada 2009;25:42–7.
[2] A myotte PR. Dust explosions happen because we believe in unicorns. Keynote Lecture, Pro-
ceedings of 13th Annual Symposium, Mary Kay O’Connor Process Safety Center, Texas A&M
University, College Station, TX; October 26–28, 2010. pp. 3–30.
[3] K letz T. Equipment and procedures that cannot do what we want them to do. Workshop Notes
and Slides, Hazards XXI, Institution of Chemical E ngineers, Manchester, UK; November 9,
2009.
[4] A myotte PR. Facing the pentagon. Industrial Fire Journal. First Quarter 2010;34–5.
[5] A myotte PR, Eckhoff RK. Dust explosion causation, prevention and mitigation: an overview.
Journal of Chemical Health & Safety 2010;17:15–28.
[6] E ckhoff RK. Dust explosions in the process industries, 3rd ed. Boston, MA: Gulf Professional
Publishing/Elsevier; 2003.
[7] B arton J, editor. Dust explosion prevention and protection. A practical guide. Rugby, UK:
Institution of Chemical Engineers; 2002.
[8] K letz T, Amyotte P. Process plants. A handbook for inherently safer design, 2nd ed. Boca
Raton, FL: CRC Press, Taylor & Francis Group; 2010.
[9] A bbasi T, Abbasi SA. Dust explosions—cases, causes, consequences, and control. Journal of
Hazardous Materials 2007;140:7–44.
[10] E ckhoff RK. Understanding dust explosions. The role of powder science and technology.
Journal of Loss Prevention in the Process Industries 2009;22:105–16.
[11] E ckhoff RK. Dust explosion prevention and mitigation. Status and developments in basic
knowledge and in practical application. International Journal of Chemical Engineering 2009.
Article ID 569825, 12 pp.
[12] M KOPSC. A frontiers of research workshop. Process safety research agenda for the 21st cen-
tury. A policy document developed by a representation of the global process safety academia
(October 21–22, 2011). College Station, TX: Mary Kay O’Connor Process Safety Center,
Texas A&M University System; 2012.
[13] C SB. Case study—Hoeganaes Corporation: Gallatin, TN—metal dust flash fires and hydro-
gen explosion. Report No. 2011-4-I-TN. Washington, DC: U.S. Chemical Safety and Hazard
Investigation Board; 2011.
Chapter 2
Myth No. 1 (Fuel): Dust Does
Not Explode
An Introduction to Dust Explosions. http://dx.doi.org/10.1016/B978-0-12-397007-7.00002-1
Copyright © 2013 Elsevier Inc. All rights reserved. 9
10 An Introduction to Dust Explosions
In this chapter we explore the notion that dust does not—or cannot—explode.
Possible reasons for the existence of this myth are identified, and suggestions
for refuting it on the basis of observable facts are given.
No blame or ulterior motives are ascribed to holding the belief that dusts
do not explode; this comment applies equally to all the myths described in this
book. My experience has been, however, that many people are surprised to learn
that dust explosions can and do occur. It may be a friend who is amused to hear
that I have spent the better part of my professional career working in the field of
dust explosion prevention and mitigation. Or it may be a client who was previ-
ously unaware that the material we had just tested for the client company did
in fact explode and could cause significant harm should it do so in an industrial
setting.
I recall one such client who, after learning that the powder his employees
were handling was explosible, remarked that I had just sent the company down a
very expensive path of installing explosion prevention and protection measures.
This seemed a curious comment given that it was not me who had decided to
process the particular material, and it was certainly not me who had made the
material explosible in the first place. I was reminded of Richard Feynman’s
closing passage in his minority report on the causes of the Challenger space
shuttle disaster [1] (p. 169), with underlining added here for emphasis:
For a successful technology, reality must take precedence over public relations, for nature
cannot be fooled.
Perhaps it is the word itself—dust—that creates the perception of particulate
matter being non-explosible. In a household context, dust is indeed likely to be
seen more as a nuisance from the perspectives of cleanliness and allergy avoid-
ance. The word gas, on the other hand, may impart a more general sense of
hazard awareness because of its use in relation to applications such as cooking
(stoves) and motor vehicles (internal combustion engines).
It does appear there is a stronger linkage between the words gas and explo-
sible than between the solid counterpart dust and explosible. Note that in this
book I have used explosible to denote a substance capable of exploding, but
also one which is not intended to explode under industrial conditions. This is to
distinguish such materials from an explosive such as dynamite which is intended
to explode under controlled conditions to achieve a desired objective (e.g., rock
blasting for roadway or tunnel construction).
2.1 DUST DEFINITION
Morgan and Supine [2] note the distinction made by the U.S. National Fire
Protection Association between a dust and a combustible dust. NFPA 68 [3]
defines a dust as any finely divided solid, 420 µm or 0.017 in. or less in diameter
(i.e., material capable of passing through a U.S. No. 40 Standard Sieve). A
combustible dust is defined as a combustible particulate solid that presents a
Chapter | 2 Dust Does Not Explode 11
fire or d eflagration hazard when suspended in air or some other oxidizing
medium over a range of concentrations, regardless of particle size or shape [3].
So essentially, one should not view a defined boundary of 420 µm as a sharp
delineation between dusts that are explosible and those that are non-explosible.
What determines whether a given particulate material represents a dust explo-
sion hazard are its actual chemical composition (Section 2.2) in addition to
physical parameters such as particle size (Chapter 6) and particle shape. As
noted by Febo [4] (p. 62):
…simply looking at a dust is not necessarily a reliable way to identify a combustible dust
hazard.
For example, with respect to particle shape and its effect on explosibility,
Figures 2.1 and 2.2 show scanning electron microscope (SEM) images of sam-
ples of polyethylene. Given the discussion to follow in Chapter 3, these samples
must be considered (at least initially) to be explosible based solely on their com-
position. But what of the particle size? Again, based on the discussion in Chap-
ter 6 of the current book, because both samples pass through a 200-mesh sieve
(nominally < 75 µm), they are certainly fine enough to support combustion.
Concerning particle shape, the fibrous (or flocculent) nature of the sample
shown in Figure 2.2 should not be used to make the assessment that it is non-
explosible simply because it does not look like the sample shown in Figure 2.1
(which is composed of near-spherical particles). Such a conclusion could have
disastrous consequences given that both polyethylene samples were determined
to be explosible and capable of generating explosion overpressures of approxi-
mately 7 bar(g) (i.e., seven times atmospheric pressure) and rates of pressure
rise as high as 300–400 bar/s in a volume of 20 L [5].
FIGURE 2.1 SEM micrograph of –200 mesh spherical polyethylene sample [5].
