Dust Explosion Causation,Prevention and Mitigation,An Overview

RESOURCE ARTICLE

Dust explosion causation,prevention and mitigation:An overview

Paul R.Departmand Appversity, 1fax, Nopaul.am

Rolf K.Departmogy, Uniway andMalmo,

1871-5532

doi:10.101

The current paper gives a general overview of factors that can cause a dust explosion and the means by whichsuch an event can be prevented and mitigated. Important explosibility parameters (e.g., maximum explosionpressure and standardized maximum rate of pressure rise) are described in terms of their relation toexplosion causation, prevention and mitigation. Causation is further explained by means of the fire triangleand the explosion pentagon, and standard risk reduction measures are placed in a hierarchical arrangementincorporating inherent safety, passive engineered safety, active engineered safety, and procedural safety. Theimportance of safety culture and a safety management system approach are emphasized by reference to anindustrial case study.

By Paul R. Amyotte,Rolf K. Eckhoff

INTRODUCTION

A dust explosion can occur when par-ticulate solid material is suspended inair and a sufficiently energetic ignitionsource is present. The consequencesare often similar to those arising froma gas explosion in terms of impact onpeople, physical assets and businessproduction. While most industrialpractitioners are familiar with at leastthe basic concepts of gas explosions(e.g., the need for a fuel, oxidant andignition source), the same cannot besaid for dust explosions.

The primary distinguishing factorbetween dust and gas explosions isthe phase of the fuel itself—solid versusgaseous. Particle size is therefore adominant issue in efforts aimed at pre-

Amyotte is affiliated with theent of Process Engineeringlied Science, Dalhousie Uni-360 Barrington Street, Hali-

va Scotia, Canada (e-mail:[email protected]).

Eckhoff is affiliated with theent of Physics and Technol-versity of Bergen, Bergen, Nor-Tyrens AB - ØSA Fire & Risk,Sweden.

/$36.00

6/j.jchas.2009.05.002

venting dust explosions and mitigatingtheir consequences. The NationalFire Protection Association (NFPA)defines a dust as any finely dividedsolid, 420 mm or 0.017 in. or less indiameter (i.e., material capable of pas-sing through a U.S. No. 40 StandardSieve).1 Since the range of explosibleparticle sizes for a given material canbe quite large, this definition high-lights the importance of consideringthe particle size distribution in addi-tion to a mean or median particle dia-meter. Further, the shape for which agiven material poses a dust explosionhazard may not be limited to sphericalor near-spherical particles, but couldinclude flakes, fibres and flocculentforms.

Dust Explosion Occurrence

One of the first recorded accounts of adust explosion was written by CountMorozzo2 in 1795, and gave a detailedaccount of an explosion in a flourwarehouse in Turin, Italy (as describedby Piccinini3 and Eckhoff4). In 1845,Faraday and Lyell5 elucidated the keyrole of coal dust in the devastatingexplosion in the Haswell (UK) coalmine the previous year.6 Fast-forward-ing to the 21st century, dust explosionsremain a persistent and damagingindustrial occurrence. The US Chemi-cal Safety and Hazard InvestigationBoard (CSB) has recently completeda series of reports dealing with inves-tigations into the causes of serious dust

� Division of Chemical Health

explosion incidents that occurred inthe United States during 2003.7–9 Afourth CSB report10 gives the findingsof a study of dust explosions in generalindustry which was initiated followingthe three catastrophic incidents in2003. At the time of writing the currentmanuscript, the CSB is engaged ininvestigating the 2008 explosion andfire at the Imperial Sugar refinery nearSavannah, GA.

Dust explosion incidents are not,however, restricted to coal mines andfood-processing facilities; nor are theyrestricted to the scenario of an indus-trial disaster. Frank11 gives incidentdata reported by the US CSB andFM Global, which illustrate that dustexplosions have occurred, for example,in the following industries with theindicated typical commodities:

� W

and

ood and paper products (dustsfrom sawing, cutting, grinding, etc.);
� G rain and foodstuffs (grain dust,
flour);
� M etal and metal products (metal
powders and dusts);
� P ower generation (pulverized coal,
peat and wood);
� R ubber; � C hemical process industry (acetate
flake, pharmaceuticals, dyes, pesti-cides);
� P lastic/polymer production and
processing;
� M ining (coal, sulphide ores, sul-
phur); and

Safety of the American Chemical Society 15Elsevier Inc. All rights reserved.

mailto:[email protected]






http://dx.doi.org/10.1016/j.jchas.2009.05.002

� T
extile manufacturing (linen flax,cotton, wool).
Objectives of Paper

The primary objective of the currentpaper is to provide a general overviewof the mechanisms by which dustexplosions originate, and the meth-odologies by which they can be pre-vented and their consequencesmitigated. The paper is intended forthe generalist audience in industry.Other resources are available for spe-cialists in industrial loss preventionand dust explosion research. Forexample, recent reviews cover in detailcase histories, causes, consequencesand control of dust explosions,12 therole of powder science and technologyin understanding dust explosion phe-nomena,6 and the status of develop-ments in basic knowledge andpractical application with respect todust explosion prevention and mitiga-tion.13

An additional objective of the cur-rent paper is to link the fundamentalsof dust explosion causation, preven-tion and mitigation with the conceptsof safety culture, a safety managementsystem, and inherent safety. Based onthe experience of the authors, it iscritically important to place technicalknowledge in a context of demon-strable management commitment todust explosion risk reduction.4,14–16

DUST EXPLOSION CAUSATION

As a first step to understanding dustexplosion causation, it is important todistinguish between a dust explosionhazard and a dust explosion risk.While the terms hazard and risk areoften used interchangeably, they repre-sent very different concepts. Func-tional definitions of each term aregiven by Wilson and McCutcheon17:

Hazard: The potential of a machine,equipment, process, material or physi-cal factor in the working environmentto cause harm to people, environment,assets or production.Risk: The possibility of injury, loss orenvironmental incident created by ahazard. The significance of risk is afunction of the probability (or likeli-

16

hood) of an unwanted incident and theseverity of its consequences.

It is clear from the above definitionsthat risks are determined by assess-ment of the likely consequences ofidentified hazards. Thorough hazardidentification is, therefore, key to theeffective management of risk; one can-not manage the risk arising from ahazard that has not been identified.With respect to dust explosions, it isessential to determine whether a givenmaterial actually constitutes an explo-sion hazard, and if so—the degree ofhazard as represented by variousexplosibility parameters. Only thencan appropriate risk reduction mea-sures aimed at prevention and mitiga-tion be devised and implemented.Expressed from a practical, industrialperspective, hazard analysis identifieswhat can go wrong, whereas risk ana-lysis assesses the probable conse-quences of these events in terms ofprobable loss of life, probable injuries,and probable loss of property, produc-tion capacity and market shares.

The above reasoning is illustrated inFigure 1. Here, the key step of hazardidentification is shown as a precursorto various explosion prevention andmitigation measures, each of whichhas been linked to one or more specificexplosibility parameters. These pointsare discussed in subsequent sections ofthe paper, as is the issue of manage-ment responsibility (as identified in theblock at the bottom centre of Figure 1).

Explosibility Parameters

The purpose of this section is to pro-vide a guide to some of the moreimportant and commonly reporteddust explosibility parameters. Para-meter values for many materials canbe found in the literature (e.g., NFPA681 and Eckhoff4) or online databases(e.g., BGIA18). Such values should,however, only be used as indications,and not as the ultimate basis for designof actual safety measures in industry(which should be based on test data forthe actual dust in question).4

When identifying dust explosionhazards, one is inevitably drawn toan examination of the material itselfin an attempt to answer questions suchas: (i) Can the dust yield dust explo-

Journal of Chemical H

sions when dispersed as a cloud in air?(ii) How high is the resulting overpres-sure if the explosion occurs at constantvolume? (iii) How quickly does thepressure rise if the explosion occursat constant volume? (iv) What concen-tration of airborne dust is needed foran explosion? (v) How much energy,or how high a temperature, is neededfor ignition? (vi) What minimum per-centage of oxygen in the atmosphere isrequired to sustain flame propagationin the dust cloud?

These questions are addressed bydetermining the basic explosibilityparameters of the dust in accordancewith Figure 1 and as shown in Table 1.It is important to recognize that theseparameters are not fundamental prop-erties of a given material. They arestrongly dependent on both materialcharacteristics (e.g., moisture contentand particle size, shape, and porosity)and experimental conditions (e.g., ves-sel volume, turbulence of the dustcloud, and applied ignition energy).The standard test methodologies(American Society for Testing andMaterials) given as examples inTable 1 represent industry-consensusapproaches to ensuring the measuredparameters are applicable to the pre-vention and mitigation of industrial-scale dust explosions.

Most of the parameters listed inTable 1 are self-explanatory, with theexception of KSt, the volume-normal-ized maximum rate of pressure rise.The parameter (dP/dt)max is of coursedependent on the volume of the explo-sion chamber, and is therefore of lim-ited use on its own. For scaling tolarger volumes, maximum rates ofpressure rise are normalized by multi-plying by the cube root of the explosionchamber volume, V:

KSt ¼�

dP

dt

�max

� V1=3 (1)

Eq. (1) is sometimes referred to asthe cubic or cube root law and KSt asthe dust constant. (The subscript ‘St’derives from the German word fordust—staub.) It is preferable, however,to refer to Eq. (1) as the cubic relation-ship and KSt as the volume-normalized(or standardized) maximum rate ofpressure rise, or simply as KSt. There

ealth & Safety, January/February 2010

Figure 1. Logic diagram for dust explosion hazard identification and risk reduction.4

Journal of Chemical Health & Safety, January/February 2010 17

Table 1. Important dust explosibility parameters and their determination and application.

ParameterTypicalunits Description

Riskcomponentaddressed

Example testmethodology

Example industrialapplications (Figure 1)

Pmax bar(g) Maximum explosion pressure inconstant-volume explosion

Consequenceseverity

ASTM E1226-05 Containment, venting,suppression, isolation,partial inerting

(dP/dt)max bar/s Maximum rate of pressure rise inconstant-volume explosion

Consequenceseverity

ASTM E1226-05 As per Pmax

KSt bar m/s Volume-normalized (or standardized)maximum rate of pressure rise inconstant-volume explosion

Consequenceseverity

ASTM E1226-05 As per Pmax

MEC g/m3 Minimum explosible (or explosive)dust concentration

Likelihood ofoccurrence

ASTM E1515-07 Control of dustconcentrations

MIE mJ Minimum ignition energy of dustcloud (electric spark)


ASTM E2019-03 Removal of ignitionsources. Groundingand bonding

MIT 8C Minimum ignition temperature ofdust cloud


ASTM E1491-06 Control of process andsurface temperatures(dust clouds)

LIT 8C Minimum ignition temperature ofdust layer or dust deposit


ASTM E2021-06 Control of process andsurface temperatures(dust layers)

MOC(LOC)

volume% Minimum (or limiting) oxygenconcentration in the atmosphere forflame propagation in dust cloud


ASTM WK1680 Inerting (with inert gas)

Table 2. KSt values measured for clouds of maize starch dust in air in differentclosed vessels and arranged according to vessel volume.4.

(dP/dt)max (bar/s) Volume (V) of apparatus (m3) KSt (bar m/s)

680 0.0012 73612 0.0012 66220 0.0012 23413 0.009 86320 0.020 87365 0.020 10010–20 0.026 3–660–80 0.026 20–25

272 0.028 8350 0.33 3472 0.95 7120 0.95 20

136 3.12 200110 6.7 20955 13.4 131

is nothing fundamental (in the sense ofan inviolable law) or constant abouteither Eq. (1) or the KSt parameter.Again, KSt is not a fundamental prop-erty of a given material.

This observation is reinforced by thediscussion in the text by Eckhoff,4 inwhich the need for appropriate deter-mination of KSt values is emphasized.An analysis of basic considerationsreveals that the cubic relationship isvalid only for geometrically similarvessels giving geometrically similarflame surfaces, and if the flame thick-ness is negligible compared to the ves-sel radius, and if the burning velocity asa function of pressure and temperatureis identical in all volumes. In view ofthese issues, it is clear that KSt from adust explosion in any arbitrary vessel isa correspondingly arbitrary measure ofdust explosion violence, because boththe turbulence and the vessel shape arearbitrary, and because the flame thick-ness is most probably considerable inrelation to the vessel radius.

Table 2 shows a selection of KSt

values for maize starch dust cloudsin air, determined in various appara-

18

tus.4 (Eckhoff4 may be consulted forthe listing of investigators and originalreferences.) The values range from 3 to6 bar m/s to over 200 bar m/s, corre-sponding to approximately an order ofmagnitude difference. Some of the dis-crepancies may arise from differencesin moisture content and effective par-


ticle size of the starch, and to differentdata interpretation (peak or meanvalues). However, differences in turbu-lence of the dust clouds and significantflame thicknesses probably play themain roles.

Therefore, when using KSt values forsizing of areas of explosion vents and


Table 3. Wood dust explosibility results.19.

Dust Particle size distribution KSt (bar m/s)

Coarse 50 weight% <1 mm 90.3 weight% <75 mm

Fine 93 weight% <1 mm 13035 weight% <125 mm16 weight% <75 mm

Figure 2. Fire triangle.

Figure 3. Fire triangle for dusts.20

for design of explosion isolation andexplosion suppression systems accord-ing to current standards, it is absolutelyessential to use data obtained from theauthorized standard test methods fordetermining KSt. Applicable methodsin this regard include those fallingunder the auspices of the AmericanSociety for Testing and Materials(ASTM), International Organizationfor Standardization (ISO), and Eur-opean Committee for Standardization(CEN).

Further guidance in the applicationof the KSt concept can be gained byexamination of Table 3, which showsexplosibility data for dust generated in awood-processing facility19 (with KSt

determined in a 20-L spherical vesselaccording to ASTM E 1226-05). In theactual process, although the coarse dustwas predominant, pockets of the finedust were found in a dead-space in aprocess unit header. Recalling that KSt

is used for sizing explosion relief vents(Table 1), it is clear that a vent designbasedon the KSt value of the coarse dustwould be inadequate for protectionfrom the effects of a dust explosioninvolving the fine wood dust.

The data in Table 3 also reinforce theneed to distinguish between materialhazard and process risk when dealingwith dust explosion phenomena. Asmentioned in the introduction, particlesize distribution is one of the key prop-erties of a dust that defines its materialhazard. Knowledge of whether a par-ticular size distribution is actuallyencountered in a given application isrequired to assess the process risk. Thishighlights the importance of gaining athorough understanding of the dusthandling process under considerationduring both normal and upset condi-tions.

Although the preceding paragraphreinforces the difference between adust explosion hazard and a dust

Journal of Chemical Health & Safety, Janua

explosion risk, it is equally importantto recognize that the two – hazard andrisk – are not independent of oneanother. This is evident from our pre-vious comment that risk can only beassessed once hazards have been iden-tified. There is thus an inevitable linkbetween the two parameters. Selectionof a dust sample for testing to see if thematerial represents an explosionhazard is often preceded by considera-tions related to process risk. For exam-ple, in plants with dust extractionsystems, it is typical to select dust sam-ples from filters. These samples will befiner than the main product and hence,will explode more violently and ignitemore readily. Here, the reasoningbehind the selection of the sample tobe tested is directly or indirectly a partof the assessment of the process risk.This again is the point being made bythe data in Table 3.

Fire Triangle

The most basic guide to understandingdust explosion causation is the familiarfire triangle (Figure 2). This simpleconcept indicates that three of thenecessary conditions for a dust explo-sion are a fuel, an oxidant and anignition source. As presented by the

ry/February 2010

IChemE20 and illustrated in Figure 3,the unique fuel requirements for a dustcan be expressed as follows: (i) the dustmaterial must be combustible, (ii) thedust must be airborne, (iii) the dustmust have a particle size distributioncapable of propagating flame whendispersed as a cloud in air, and (iv)the dust concentrations must be withinthe explosible range.

Explosion Pentagon

The explosion pentagon, as describedby Kauffman21 and illustrated inFigure 4, expands the basic fire triangleto include mixing of the fuel and oxi-dant and confinement of the mixture.The first of these additional compo-nents illustrates the previously men-tioned key difference between dustand gas explosions—a solid rather thana gaseous fuel. A gas explosion there-fore involves a homogeneous system inwhich the smallest entities of fuel andair are separated only by moleculardistances. Thorough mixing of fueland oxidant is readily achieved andgravitational effects are negligible.However, in a dust/air mixture, thedust particles are strongly influencedby gravity; an essential prerequisite fora dust explosion is the formation of adust/oxidant suspension.22 Once com-bustion of the resultant mixture occurs,confinement (partial or complete) per-mits an overpressure to develop, thusenabling a fast-burning dust flame totransition to a dust explosion.

Primary Explosions

Dust explosions usually occur inindustry inside process vessels andunits such as mills, grinders, anddryers—i.e., inside equipment wherethe conditions of the explosion penta-gon are satisfied. Such occurrences are

19

Figure 4. Explosion pentagon.21

Figure 5. Typical ranges of dust concentrations in air at normal temperature andpressure for common natural organic dusts, for maximum permissible hygienicexposure, dust explosions, and dust deposit combustion (smoldering fires),respectively.4

often called primary explosions, espe-cially if they result in secondary explo-sions external to the process unit (asdescribed in the next section). Thereason for the majority of dust explo-sions being initiated in this manner canbe understood by examining Figure 5.Here, the range of explosible dust con-centrations in air at normal tempera-ture and pressure for a natural organic

Figure 6. (a–c) Illustrati

20

dust (e.g., cornstarch) is comparedwith the typical range of maximumpermissible dust concentrations thatare relevant in the context of industrialhygiene, and with a typical density ofdeposits or layers of natural organicdusts. Clearly, the range of explosibleconcentrations is orders of magnitudegreater than the concentrations per-mitted in areas inhabited by workers.

on of the potential for dust cloud generation


Secondary Explosions

Notwithstanding the discussion in theprevious section, dust explosions dooccur in process areas, not just insideprocess units. A secondary explosioncan be initiated due to entrainment ofdust layers by the blast waves arisingfrom a primary explosion. The primaryevent might be a dust explosion origi-nating in a process unit, or could beany disturbance energetic enough todisperse explosible dust layered onthe floor and various work surfaces.An example of such an energetic dis-turbance (other than a primary dustexplosion) would be a gas explosionleading to a dust explosion. This is awell-documented phenomenon in theunderground coal mining industry,where devastating effects can resultfrom the overpressures and rates ofpressure rise generated in a coal dustexplosion that has been triggered by amethane explosion.

The required amount of layered dustwhich, once airborne, could sustain asecondary dust explosion is oftengrossly overestimated. For example,in the Westray mine explosion23

described later in this paper, one ofthe contributing factors was the pre-sence of coal dust layers several centi-metres thick throughout the mineworkings. In fact, the amount of coaldust that could be dispersed by anaerodynamic disturbance and thencombusted with the available oxygenwould have been significantly less than‘several centimetres’. This point is illu-strated in a general manner byFigure 6, which shows the implicationsof the following expression:

C ¼ ðrbulkÞ�

h

H

�(2)

from a dust layer.4


where rbulk is the bulk density of a dustlayer, h is the layer thickness, H is theheight of the dust cloud produced fromthe layer, and C is the resulting dustconcentration.

From Eq. (2) and as shown inFigure 6, a 1-mm thick layer of a dustof bulk density 500 kg/m3 on the floorof a 5-mhigh room will generate a cloudof average concentration 100 g/m3 ifdispersed evenly all over the room.6

Such a concentration is of the orderof the minimum explosible concentra-tion for many explosible dusts. Partialdispersion up to 1 m above the flooryields a dust concentration of 500 g/m3; this is a concentration that is ofthe order of the optimum concentration(i.e., the concentration producing themost devastating overpressures andrates of pressure rise) for many explo-sible dusts.

Clearly, even seemingly harmlessdust layers have the potential torapidly escalate the risk of a dust explo-sion. This observation helps to explainthe advice given by experienced indus-trial practitioners—such as: there’s toomuch layered dust if . . . you can seeyour footprints in the dust . . . you canwrite your initials in the dust. Thesecomments, although anecdotal, have afirm foundation in the chemistry andphysics of dust explosions.

Hybrid Mixtures

Hybrid mixtures consist of a flam-mable gas and a combustible dust, eachof which may be present in an amountless than its lower flammable limit(LFL)/minimum explosible concen-tration (MEC), and still give rise toan explosible mixture. The focus whendiscussing hybrid mixtures is, in fact,on admixture of a flammable gas inconcentrations below the lower flam-mable limit of the gas itself. If the LFLfor the gas is exceeded, one soon has asituation where the worst-case sce-nario for a primary explosion wouldbe a pure gas explosion.

Perhaps the most well-knownhybrid mixture is the methane/coaldust system often encountered inunderground coal mining. There arealso several examples of hybrid mix-ture formation in other industries, suchas the natural gas/fly ash system infossil-fuel burning power plants and


various hydrocarbon/resin combina-tions occurring in the production ofplastic powders.

The influence of the co-presence of aflammable gas on the explosibilityparameters of a fuel dust alone is wellestablished (e.g., Cashdollar24). Theseeffects include higher values of max-imum explosion pressure and maxi-mum rate of pressure rise (and henceKSt), and lower values of minimumexplosible concentration and mini-mum ignition energy. There is, ofcourse, already a hazard that existswhen an explosible dust is present ina quantity above its minimum explosi-ble concentration. With flammable gasadmixture, the scenario is now one ofmagnification of an already existinghazard, not the creation of a problemthat did not already exist in some formalready.

DUST EXPLOSION PREVENTION ANDMITIGATION

When selecting dust explosion preven-tion and mitigation measures, it ishelpful to employ a heuristic or frame-work for making appropriatechoices.25 The fire triangles shown inFigures 2 and 3, and the explosionpentagon shown in Figure 4, offer gui-dance in this area in addition to iden-tifying dust explosion causationfactors. For example, the triangleaffords industrial practitioners severalapproaches to explosion prevention(e.g., removal of fuel by good house-keeping and removal of electrostaticignition sources by grounding andbonding). The use of the pentagon tovisualize explosion requirements leadsto identification of measures for explo-sion mitigation such as venting (inrelief of the confinement criterion).

What is missing in the above discus-sion, however, is guidance on whichrisk reduction techniques are mosteffective and in what order the varioustechniques should be considered. Pre-vention is obviously preferred to miti-gation, but both are likely to berequired in a given application. Thequestion, then, is which of the variousmeasures spanning out from the cen-tre sphere in Figure 1 should receivepriority? The following sections

ry/February 2010

attempt to address this point by firstconsidering a general loss preventionapproach, and then tailoring thatapproach to prevention of loss fromdust explosions.

Hierarchy of Controls

Industrial loss prevention is generallyaccomplished in three ways: (i) inher-ent safety, (ii) engineered safety (pas-sive and active), and (iii) proceduralsafety.14 Engineered, or add-on, safetyinvolves the addition of safety devicesat the end of the design. A generalindustrial example would be a machineguard; with respect to the subject of thecurrent paper, an example of an engi-neered safety device is an automaticdust explosion suppression system.These safety devices do not performany fundamental operation, but aredesigned to act when a process upsetoccurs. Procedural safety measures, oradministrative controls, utilize safework practices and procedures toreduce risk. Again, a general industrialexample would be standard work prac-tices for confined space entry; withrespect to dust explosion prevention,hot-work permitting and proceduresrelated to grounding and bonding arepertinent examples in this category.

On the other hand, inherent safetyuses the properties of a material orprocess to eliminate or reduce thehazard. The fundamental differencebetween inherent safety and the othertwo categories is that inherent safetyseeks to remove the hazard at thesource as opposed to accepting thehazard and looking to prevent itsoccurrence or mitigate its effects.

Figure 7 illustrates a systematicapproach to loss prevention that hasfound general acceptance in industry.With this approach, the preferredorder of consideration for risk reduc-tion measures (from most effective toleast) is inherent, passive engineered,active engineered, and proceduralsafety. This is akin to the layer of pro-tection analysis (LOPA) concept inwhich inherently safer process designsits at the central core of the layers.Hopkins26 uses the phrase hierarchy ofcontrols to describe essentially thesame idea; i.e., that there is a hierarch-ical ordering of controls to deal withhazards, covering the spectrum from

21

Figure 7. A systematic approach to loss prevention.19

22 Journal of Chemical Health & Safety, January/February 2010

elimination (at the top of the hierar-chy) through engineering and admin-istrative (procedural) controls, to PPE(personal protective equipment) at thebottom of the hierarchy.

Inherent safety

The formal concept of inherent safetyin the process industries was first pro-posed by Trevor Kletz in the late 1970sin his Jubilee Lecture to the Society ofChemical Industry in Widnes, UK.27

(The title of his paper, what you don’thave, can’t leak, provides an aptdescription of the main thrust of inher-ent safety.) Since that time, the con-cepts of inherent safety and inherentlysafer design have made several inroadsinto the process industries. Numerousresearch and review papers have beenwritten, and a new text28 represents themost recent major publication in thesubject area. The four key principles ofinherent safety are summarized inTable 4.

Various examples of the applicationof the principles in Table 4 to dustexplosions have been given in a recentpaper by Amyotte et al.14 A brief reca-pitulation by inherent safety principlefollows:

� M

Ta

Pr

M

Su

M

Si

Jo

inimization- Avoidance of dust cloud formation

(including operation below theminimum explosible concentra-tion if possible).

- Removal of dust deposits (avoid-ance of dust layers). The paper byFrank11 is an excellent resource onthe both the importance and theeffectiveness of good housekeep-

b

in

in

b

od

m

ur

ing.

� S
ubstitution- Substituting one work procedure
for another (e.g., using an explo-

le 4. Inherent safety principles.14.

ciple

imization Use smaller quantities of heliminated. Perform a haz

stitution Replace a substance withinvolve hazardous materia

eration Use hazardous materials iinvolve less severe process

plification Design processes, processieliminating excessive use o

nal of Chemical Health & Safety, January

sion-proof vacuum in place ofsweeping with a broom to removedust accumulations).

- Replacement of bucket elevatorsand other mechanical conveyingsystems with dense-phase pneu-matic transport (if feasible).

- Substitution of process hardwarewith less hazardous materials ofconstruction (e.g., avoiding unne-cessary use of insulating materi-als).

- Substitution of a process route thatinvolves handling an explosiblepowder (e.g., earlier introductionof an inert powder that is a com-ponent of the final product).

- Substitution of the hazardousmaterial (i.e., explosible powderitself). This is often not feasiblewhen the explosible powder isthe desired product; one potentialapplication is the replacement ofpulverized coal with petroleum

aaral.ninngf

/F

coke in a utility boiler.

� M
oderation- Altering the composition of a dust
by admixture of solid inertants.- Increasing the dust particle size so

as to decrease its reactivity.- Avoiding the formation of hybrid

mixtures of explosible dusts andflammable gases.

- Limiting the effects of a processupset by using appropriate dis-
tances to separate process units.
� S
implification
- Employing the concept of error tol-
erance by designing process equip-ment robust enough to withstandprocess upsets and other undesiredevents (e.g., shock- or pressure-resis-tant design).
- E
nsuring information on the hazar-dous properties of powders is clearand unambiguous (e.g., through
Description

zardous materials when the use of sucdous procedure as few times as possibless hazardous material or processingReplace a hazardous procedure with otheir least hazardous forms or identifyg conditions.equipment, and procedures to elimin

add-on safety features and protective

ebruary 2010

effective use of Material Safety DataSheets or MSDSs).

Passive engineered safety

Passive add-on devices, if adequatelydesigned, manufactured and fitted forservice, will perform their desiredsafety function simply by their pre-sence. No actuation beyond the initi-ating event (e.g., dust explosionoverpressure) is required for a passivedevice to fulfil its intended role. Explo-sion relief venting would fall in thiscategory as would the use of physicalbarriers to isolate plant sections in anattempt to prevent domino or knock-on effects.

Active engineered safety

Active add-on devices require somedegree of detection and activation toperform their desired safety function.In addition to adequate design andmanufacturing, these devices requireproper maintenance and testing tofacilitate their reliable performance.Demand for active engineered mea-sures is intentionally intermittent,and there is thus a strong need to limitthe potential for failure when they areneeded. Examples here would includeautomatic dust explosion suppressionsystems (as previously mentioned) andmechanical isolation valves, both ofwhich employ detectors and actuatorsin addition to the actual safety device(suppressant-filled canister and metalplate, respectively).

Inerting is a dust explosion preven-tion/mitigation measure that could beclassified as either inherent or activeengineered safety depending on themethod of application. As previouslyindicated, addition of an inert solid toan explosible dust so as to render the

h materials cannot be avoided orle when the procedure is unavoidable.route with one that does notne that is less hazardous.processing options that

ate opportunities for errors bydevices.

23

resulting mixture nonexplosible, is anexample of the inherent safety princi-ple of moderation—albeit through theprocedural measure of adding the inertmaterial. An example here is theadmixture of inert limestone or dolo-mite to explosible coal dust as is prac-ticed in underground coal mining. Onthe other hand, inerting or partialinerting by means of a nonreactivegas would likely be viewed as activeengineered safety because of the needfor physical devices for inert gas addi-tion and monitoring.

Procedural safety

Although there is a strong human ele-ment to the previously described levelsin the hierarchy of controls – after all, itis human beings who design, manufac-ture and install safety devices – thecategory of procedural safety is wherethe performance of plant personnelbecomes critical to the success or fail-ure of a given safe work practice orprocedure. The potential for humanerror places procedural safety at thebottom of the hierarchy of controls;this fact must be recognized and man-aged by comprehensive considerationof the human factors involved in per-forming a safety-oriented task.

Procedural dust explosion riskreduction measures typically relate toattempts to remove ignition sourcesfrom the workplace. Examples includepermit-to-work, and the previouslymentioned hot-work permitting, andgrounding and bonding. Althoughabsolutely necessary as a line ofdefence against dust explosion occur-rence and consequences, it is not advi-sable to rely solely on ignition sourceremoval in this regard. Potential igni-tion sources abound in industry andsometimes arise as a result of a poorlydesigned or poorly followed proce-dure.

Summary of Prevention and MitigationMeasures

Eckhoff6 has previously reported a tab-ular listing of the common means ofpreventing and mitigating dust explo-sions. With the analysis in the previoussections of the current paper, thesemeans can now be categorized usingthe hierarchy of controls as shown inTable 5. There are several points to

24

note in using Table 5 as a selectionguide for dust explosion risk reductionmeasures:

� I
nherent safety (inherently saferdesign) is the most effective way todeal with a dust explosion hazard.To paraphrase Kletz27: what youdon’t have, can’t explode.
� I
nherent safety achieves its greatestimpact when considered early in thedesign life cycle. Once a process unitis built to withstand only moderatepressure excursions, it is likely toolate to consider an explosion pres-sure-resistant design for that parti-cular unit.
� S
ome inherent safety options maynot be feasible in a given application.For example, a chemically inert dustcannot likely be substituted for anexplosible dust if the latter is theactual desired product. But again,if the relevant inherent safety ques-tions are not asked, then potentialprocess or product alternatives can-not be explored.
� I
nherent safety is not a stand-aloneconcept. It works through a hier-archical arrangement in concertwith engineered (passive and active)and procedural safety to reduce risk.
� T
he hierarchy of controls does notinvalidate the usefulness of engi-neered and procedural safety mea-sures. Quite the opposite—thehierarchy of controls recognizesthe importance of engineered andprocedural safety by highlightingthe need for careful examination ofthe reliability of both mechanicaldevices and human actions. Theseconsiderations must be incorporatedinto the dust explosion risk assess-ment process.
Role of Management

The discussion to this point has con-sidered the technical knowledgeneeded to reduce the risk of a dustexplosion: (i) thorough hazard identi-fication in terms of causation factorsand explosibility parameters, (ii) mea-sures for preventing occurrence, and(iii) measures for mitigating the con-sequences. The following sections dealwith the important matters of safetyculture and safety management sys-tems. In effect, these topics determine


whether a company has the will toproperly implement the above techni-cal knowledge, and to do so in a sys-tematic, organized manner. The finalsection gives a brief case study thatillustrates what can happen whenthere is no apparent safety culture orsafety management system.

Safety culture

The fundamental issue of whether acompany (in particular, its senior man-agers) believes it is possible to achievea higher standard of safety – in essencewhether a company believes safety is‘the right thing to do’ – has recentlybeen addressed in the excellent bookby Andrew Hopkins. Hopkins26

describes three concepts that addressa company’s cultural approach tosafety, and makes the argument thatthe three are essentially alternativeways of talking about the same phe-nomena: (i) safety culture, (ii) collec-tive mindfulness, and (iii) risk-awareness. He further defines the con-cept of a safety culture as embodyingthe following subcultures: (i) a report-ing culture in which people reporterrors, near-misses, and substandardconditions and practices, (ii) a justculture in which blame and punish-ment are reserved for behaviour invol-ving defiance, recklessness or malice,such that incident reporting is not dis-couraged, (iii) a learning culture inwhich a company learns from itsreported incidents, processes informa-tion in a conscientious manner, andmakes changes accordingly, and (iv)a flexible culture in which decision-making processes are not so rigid thatthey cannot be varied according to theurgency of the decision and the exper-tise of the people involved.

Safety culture measurement requiresthe use of appropriate indicators.There has been much recent discussionin the literature on safety culture indi-cators (lagging and leading), and sig-nificant efforts aimed at developingsuitable indicators have been under-taken by organizations such as theHealth and Safety Executive in theUK and the Center for Chemical Pro-cess Safety of the American Institute ofChemical Engineers. An increasinglycommon thought promoted by Hop-kins and others15 is that safety culture


Table 5. A hierarchical view of various means of preventing and mitigating dust explosions.

Explosion prevention

Explosion mitigationPreventing explosible dust clouds Preventing ignition sources

Process design to prevent undesiredgeneration of dust clouds andparticle size reduction andsegregation

Smouldering combustionin dust, dust fires

Good housekeeping (dust removal/cleaning)

Procedural Safety—may alsoinvolve aspects of InherentSafety or Engineered Safety

Mitigation with respect to secondarydust explosions; prevention with respectto primary dust explosions

Inherent Safety—Minimization,Substitution, Moderation,Simplification

Inherent Safety—Minimization

Keeping dust concentrationoutside explosible range

Other types of open flames(e.g., hot work)

Explosion-pressure resistant construction

Inherent Safety—Minimization Procedural Safety—may alsoinvolve aspects of InherentSafety or Engineered Safety

Inherent Safety—Simplification

Inerting of dust cloud byadding inert dust

Hot surfaces (electrically ormechanically heated)

Explosion isolation (sectioning)

Inherent Safety—Moderation Procedural Safety—may alsoinvolve aspects of InherentSafety or Engineered Safety

Inherent Safety—Moderation (e.g., unitsegregation, product choke, etc.) if notusing mechanical devices. If mechanicaldevices are used to isolate plant sections,classification would be EngineeredSafety—Passive in the case of physicalbarriers, or Engineered Safety—Active inthe case of isolation valves.

Intrinsic inerting of dust cloudby combustion gases

Heat from mechanical impact(metal sparks and hot-spots)

Explosion venting

Engineered Safety—Active Procedural Safety—may alsoinvolve aspects of InherentSafety or Engineered Safety

Engineered Safety—Passive

Inerting of dust cloud byN2, CO2 and rare gases

Electric sparks and arcs andelectrostatic discharges

Automatic explosion suppression

Engineered Safety—Active Procedural Safety—may alsoinvolve aspects of InherentSafety or Engineered Safety

Engineered Safety—Active

Partial inerting of dust cloud by inert gasEngineered Safety—Active

indicators must measure the effective-ness of the various measures compris-ing the risk control system. In otherwords, safety indicators must berelated to the elements making upthe safety management system.

Safety management systems

Safety management systems are recog-nized and accepted worldwide as best-practice methods for managing risk.They typically consist of 10–20 pro-gram elements that must be effectivelycarried out to manage the risks in anacceptable way. This need is based onthe understanding that once a risk isaccepted, it does not go away; it isthere waiting for an opportunity tohappen unless the management sys-tem is actively monitoring company


operations for concerns and takingproactive actions to correct potentialproblems.

As a primary corporate objective,dust explosion prevention and mitiga-tion would typically fall within thescope of a Process Safety Managementsystem (i.e., a management system forprocess-related hazards such as fire,explosion, release of toxic materials,etc.) One such system widely used inindustry is termed PSM, Process SafetyManagement—where PSM is definedas the application of managementprinciples and systems to the identifi-cation, understanding and control ofprocess hazards to prevent process-related injuries and accidents. Thesuite of PSM elements is shown inTable 6.

ry/February 2010

In light of the previous discussion onthe hierarchy of controls, a strong casecan be made for the need to demon-strate a commitment to the principlesof inherent safety within each of thePSM elements listed in Table 6.16 Thus,within element 6, process risk manage-ment, the hierarchical arrangement ofdust explosion prevention and mitiga-tion measures shown in Table 5 wouldfind direct application. Additionally,within element 8, training and perfor-mance, a strong safety culture wouldnecessitate the provision of workplacetraining in dust explosion hazards, andhow these hazards can be alleviated byapplication of, for example, the inher-ent safety principle of minimizationthrough effective housekeeping. Asillustrated by the analysis that follows

25

Figure 8. Damage to portal at No. 1 main, Westray coal mine.29

Table 6. Elements of Process SafetyManagement, PSM.16.

No. Element

1 Accountability: objectives andgoals

2 Process knowledge anddocumentation

3 Capital project review anddesign procedures

4 Process risk management5 Management of change6 Process and equipment integrity7 Human factors8 Training and performance9 Incident investigation

10 Company standards, codesand regulations

11 Audits and corrective actions12 Enhancement of process

safety knowledge

for element 9, similar observations canbe made for the other PSM elements inTable 6.

In a previous paper, Amyotte et al.15

have demonstrated that three of Hop-kins’ four safety subcultures (reporting,just and learning) have an explicit linkto the PSM element of incident inves-tigation. With respect to the subject ofthe current paper, a company’s com-mitment to just and reporting cultureswill ultimately be expressed in thenumber of dust explosion incidentsthat are reported. In the spirit of aleading indicator, it would be impor-tant to also measure the number ofnear-miss and at-risk behaviourreports involving combustible pow-ders. The outputs of reporting andinvestigating will manifest themselvesas a measure of commitment to a learn-ing culture; lessons learned is a keyphrase in the industrial lexicon. Theidea of learning from experienceextends beyond the realm of incidentinvestigation and into other safetymanagement system elements (e.g.,process risk management, manage-ment of change, and enhancement ofprocess safety knowledge).

It may be tempting to dismiss talk ofsafety culture and safety managementsystems as being unimportant in rela-tion to the chemistry, physics and engi-neering of dust explosions. Further,safety culture might be viewed by someas merely the current ‘hot topic’ in

26

industrial safety—i.e., a relatively newconcept that, given time, will bereplaced by something else. On thefirst matter, the next section will hope-fully dispel any notion that well-estab-lished technical knowledge, in theabsence of a strong safety culture andmanagement system, is sufficient toensure an acceptably low dust explo-sion risk. On the second point, we offerthe following quote from the last para-graph of Count Morozzo’s report2

describing the Turin flour warehouseexplosion mentioned in the introduc-tion:

Ignorance of the fore-mentioned circum-stances, and a culpable negligence ofthose precautions which ought to betaken, have often caused more misfor-tunes and loss than the most contrivingmalice. It is therefore of great importancethat these facts should be universallyknown, that public utility may reap fromthem every possible advantage.

The above passage makes an elo-quent case for the importance of astrong safety culture, incident investi-gation, and the sharing of lessonslearned. It is instructive to also notethat it was written over 200 years ago.

Case study—Westray coal mineexplosion

The Westray coal mine explosionoccurred in Plymouth, Nova Scotia,Canada, on May 9, 1992, killing 26


miners.23 An indication of the destruc-tive overpressures generated under-ground can be seen in Figure 8,which shows surface damage at themine site. The methane levels in themine were consistently higher thanregulations, which was caused byinadequate ventilation in the mine.Dust accumulations also exceeded per-missible levels due to inadequatecleanup of coal dust; additionally,there was no crew in charge of rockdusting (inerting the coal dust withlimestone or dolomite). These andmany other factors contributed to thepoor work conditions that continuallyexisted in the Westray mine and madeit the site of an incident waiting tohappen. All of these substandard con-ditions and practices could be attribu-ted to the lack of concern thatmanagement had towards safety issuesin the mine, which was one of theprimary root causes of the problemat Westray.

The question may arise as to whethera coal dust explosion in an under-ground mine, which was initiated bya methane explosion, is a typical casein a dust explosion context. The choiceof this particular case study is, how-ever, regarded as fully justified giventhat it has been so well-documented29

and thoroughly analysed.23

Lack of adequate loss preventionand management is generally due todeficiencies in one or more of three


Table 7. Hazard avoidance possibilities categorized by inherent safety principle.15.

Principle Recommendation to avoid hazard

Minimize Methane: degasification (extraction of methane prior to mining)Coal dust: housekeeping program for continuous removalFuel storage: elimination of underground storageIgnition sources: replacement of nonflameproof equipment (i.e., minimization of ignition sources bysubstitution of equipment)Shift length: reduction from 12 h

Substitute Auxiliary ventilation system: forcing, rather than exhaust, system for adequate airflow to clear methane fromthe working face of the mineMain ventilation fan: alternate design and location so as not to pick up dust and other debris from the coalreturn conveyor belt.

Moderate Coal dust: purchase and maintenance of an adequate inventory of rock dust; implementation of a programfor rock dusting undergroundCoal dust: roadway consolidation (a process to control the formation and dispersal of dust on mineroadways by application of rock dust, moisture-absorbing material and a binding agent)

Simplify Methane: installation of a reliable, robust mine air monitoring system

areas–the safety management systemitself, the standards identified and setfor the safety management system, andthe degree of compliance with suchstandards.15 A particular managementsystem element may have missing com-ponents or may be entirely absent;alternatively the management systemelement may be present to somedegree, but could have inappropriatestandards–or perhaps standards forwhich there is little or no compliance.

Management system elements(reference Table 6) that contributedto the Westray explosion includeinadequate:

� M

Jo

anagement commitment andaccountability to safety matters(which is a key element in establish-ing an effective company safety cul-ture).
� M anagement of change procedures. � I ncident investigation (including
near-miss reporting and investiga-tion).
� T raining (orientation, safety, task-
related, etc.).
� T ask definition and safe work prac-
tices and procedures.
� W orkplace inspections and more
proactive hazard identificationmethodologies.
� P rogram evaluation and audits.
System standards that contributed
to the Westray explosion includestandards (i.e., levels of performance)
urnal of Chemical Health & Safety, Janua

relating to virtually all the system ele-ments listed above, including inade-quate:

� C

ry

oncern expressed by managementtoward safety matters (in terms ofthe standard of care one would rea-sonably expect and which, from alegal perspective, should be consid-ered mandatory).
� F ollow-through on inspections for
substandard practices and condi-tions.
� A ction on hazard reports submitted
by employees.
� J ob instructions for employees. � E quipment maintenance. � S cheduling of management/
employee meetings to discuss safetyconcerns.

Compliance factors that contributedto the Westray explosion include:

� P
oor correlation between manage-ment actions and official companypolicy concerning the relationshipbetween safety and production (asevidenced by the same managementpersonnel holding responsibility forboth production and undergroundsafety). � I nadequate compliance to industry
practice and legislated standardsconcerning numerous aspects ofcoal mining: methane concentra-tions, rock dusting, control of igni-tion sources underground, etc.

/February 2010

With reference to dust explosioncausation, prevention and mitigation,
the hierarchy of controls (in particularthe inherent safety control level) wasessentially ignored at the Westray site.Had there been a commitment to theprinciples of inherent safety, some ofthe hazard avoidance recommenda-tions given in Table 7 would have beenimplemented. It is particularly poign-ant to note that all of the measureslisted in Table 7 are well known andare commonly practiced in the under-ground coal mining industry.
CONCLUSION

Dust explosions occur in a variety ofindustries and have a recorded historystretching back over 200 years. InNorth America, a series of high-profiledust explosions investigated by the USCSB have renewed efforts to under-stand their causation, prevention andmitigation. While the dust explosionhazard may exist for many powdershandled in industry, the risk of anexplosion is a function of likelihoodand consequence severity considera-tions reflected in a number of impor-tant explosibility and ignitabilityparameters of dust clouds. Theseinclude the (i) maximum explosionpressure and maximum rate of rise ofthe explosion pressure in standardizedclosed-vessel tests (yielding also thevolume-normalized maximum rate ofpressure rise), (ii) minimum explosible

27

dust concentration, (iii) minimum(limiting) oxygen concentration ofthe atmosphere for flame propagation,(iv) minimum spark ignition energy,and (v) minimum dust cloud ignitiontemperature. In addition, knowing theminimum ignition temperatures ofdust layers and dust deposits for var-ious layer thicknesses and depositvolumes is important to prevent openand smoldering dust fires.

A dust explosion occurs when anexplosible dust cloud (consisting ofan adequately mixed fuel and oxidant)is formed and ignited by a sufficientlyenergetic ignition source in a confinedor partially confined environment.Such explosions originate as either pri-mary or secondary events, and mayalso involve the co-presence of a flam-mable gas (leading to the creation of ahybrid mixture).

Dust explosion prevention and miti-gation measures can be hierarchicallyorganized from most to least effectivein terms of measures related to: inher-ent safety (minimization, substitution,moderation and simplification), pas-sive engineered safety, active engi-neered safety, and procedural safety.Consideration of all levels in this hier-archy of controls is required for effec-tive dust explosion risk reduction.

Equally, if not more important todust explosion control, is the key roleplayed by senior management in ensur-ing a strong safety culture and an effec-tive safety management system.Technical knowledge without thecommensurate management commit-ment and program to ensure imple-mentation of such knowledge isdoomed to failure, as evidenced bythe 1992 Westray mine explosion.

ACKNOWLEDGEMENTSThe authors wish to gratefully acknowl-edge the funding agencies and indus-trial companies that have supportedtheir research efforts over the years.

28

REFERENCES1. NFPA 68. Standard on Explosion

Protection by Deflagration Venting,2007 Edition; National Fire Protec-tion Association: Quincy, MA,2007.

2. Morozzo, C. Account of a ViolentExplosion Which Happened in theFlour-Warehouse, at Turin, Decemberthe 14th, 1785; To Which are AddedSome Observations on SpontaneousInflammations; From the Memoirs ofthe Academy of Sciences of Turin. TheRepertory of Arts and Manufactures:London, 1795.

3. Piccinini, N. Account of a ViolentExplosion; Politecnico di Torino; Tur-in, Italy, 1996.

4. Eckhoff, R. K. Dust Explosions in theProcess Industries, 3rd ed. Gulf Profes-sional Publishing/Elsevier; Boston,2003.

5. Faraday, M.; Lyell, C. Philos. Mag.1845, 26, 16.

6. Eckhoff, R. K. J. Loss Prev. Process Ind.2009, 22(1), 105.

7. CSB. Investigation Report – Dust Ex-plosion – West Pharmaceutical Ser-vices, Inc., Report No. 2003-07-I-NC;U.S. Chemical Safety and Hazard In-vestigation Board: Washington, DC,2004.

8. CSB. Investigation Report – Combus-tible Dust Fire and Explosions – CTAAcoustics, Inc., Report No. 2003-09-I-KY; U.S. Chemical Safety and HazardInvestigation Board: Washington, DC,2005.

9. CSB. Investigation Report – Alumi-num Dust Explosion – HayesLemmerz International-Huntington,Inc., Report No. 2004-01-I-IN; U.S.Chemical Safety and Hazard Investi-gation Board: Washington, DC,2005.

10. CSB. Investigation Report—Combusti-ble Dust Hazard Study, Report No.2006-H-1; U.S. Chemical Safety andHazard Investigation Board: Washing-ton, DC, 2006.

11. Frank, W. L. Process Saf. Progr. 2004,23(3), 175.

12. Abbasi, T.; Abbasi, S. A. J. Hazard.Mater. 2007, 140(1–2), 7.

13. Eckhoff, R. K. Int. J. Chem. Eng., inpress.


14. Amyotte, P. R.; Pegg, M. J.; Khan, F. I.Process Saf. Environ. Protect. 2009,87(1), 35.

15. Amyotte, P.; Khan, F.; Demichela, M.;Piccinini, N. Paper 0114, in NinthInternational Probabilistic Safety As-sessment and Management Conference(PSAM 9), Hong Kong, China, 2008.

16. Amyotte, P. R.; Goraya, A. U.; Hender-shot, D. C.; Khan, F. I. Process Saf.Progr. 2007, 26(4), 333.

17. Wilson, L.; McCutcheon, D. IndustrialSafety and Risk Management; Univer-sity of Alberta Press; Edmonton, AB,2003.

18. BGIA. GESTIS-DUST-EX, Database:Combustion and Explosion Character-istics of Dusts. Available at: http://www.dguv.de/bgia/en/gestis/expl/in-dex.jsp [March 18, 2009].

19. Amyotte, P. R.; Pegg, M. J.; Khan, F. I.;Nifuku, M.; Yingxin, T. J. Loss Prev.Process Ind. 2007, 20(4–6), 675.

20. IChem, E. Dust Explosion Hazards,Video Training Package 022; Institu-tion of Chemical Engineers; Rugby,UK, 1993.

21. Kauffman, C. W. Fuel-Air Explosions;Lee, J. H. S. & Guirao, C. M. Ed.,Fuel-Air Explosions; University of WaterlooPress: Waterloo, ON, Canada, 1982p.305–347.

22. Amyotte, P. R.; Chippett, S.; Pegg, M. J.Progr. Energy Combust. Sci. 1988, 14(4),293.

23. Amyotte, P. R.; Oehmen, A. M. ProcessSaf. Environ. Protect. 2002, 80(1), 55.

24. Cashdollar, K. L. J. Loss Prevent.Process Ind. 2000, 13(3–5), 183.

25. Amyotte, P. R.; Khan, F. I.; Dastidar, A.G. Chem. Eng. Progr. 2003, 98(10), 36.

26. Hopkins, A.; Safety. Culture and Risk:The Organizational Causes of Disas-ters; CCH Australia Limited; Sydney,Australia, 2005.

27. Kletz, T. A. Chem. Ind. 1978, 6, 287.28. Center for Chemical Process Safety

(CCPS). Inherently Safer Chemical Pro-cesses: A Life Cycle Approach, 2nd ed.;John Wiley & Sons, Inc.: Hoboken, NJ,2009.

29. Richard, K. P. Justice. The WestrayStory—A Predictable Path to Disaster,Report of the Westray Mine PublicInquiry; Province of Nova Scotia:Halifax, NS, Canada, 1997.





Documents

Dust Explosion Causation,Prevention and Mitigation,An Overview