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In the wake of recent tragic and highlypublicized dust explosions, companies areasking, “Could that happen here?” and

“What can I do to prevent such an incidentat my facility?” One approach is to man-age dust explosion hazards as though theywere subject to OSHA’s Process SafetyManagement (PSM) requirements (29 CFR1910.119), even though dust hazards oftenare not covered under this regulation.  The PSM rule’s 14 individual elementscan be grouped into a three-step risk man-agement strategy:

1. Understand your process.  2. Identify the hazards of your pro-cess.  3. Implement the means to reduce thelikelihood and magnitude of the hazards.

The central pillar of PSM is the processhazard analysis (PHA) in that it brings

all elements together. All of the requiredprocess information is used to analyze thehazards in the PHA. In addition, follow-ing the review of the hazards, the existingand proposed safeguards are documentedin the PHA. Similarly, the control of dustexplosion hazards centers on the dust haz-ard assessment. As with PSM, the samethree steps are integral to the dust hazardassessment and form the basis for mitiga-tion of dust explosion hazards.

Understand your process  The process safety information ele-ment from PSM requires a covered pro-cess to keep current information coveringthe process chemistry, technology andthe equipment. The physical propertiesof the materials handled and the poten-tial for them to react with other materialsis part of this basic information, which iskey to managing the hazards. A facilitythat handles dust should know what theyare handling along with physical proper-

ties and the potential to react, ignite and/or explode.  In a recent audit of a facility that pro-duces inorganic water treating chemicals,the audit team observed a wide varietyof packaged solids that were used in theprocess. When asked if any of the solidsare combustible, the facility personnelanswered that there are no fire hazards inthe plant. As the audit continued with awalk through of the facility, a substantialsupply of a cellulose-based additive wasobserved, which was clearly marked as a

dust explosion hazard. This hazard wasdiscovered in a review of the MaterialSafety Data Sheets (MSDS). The first step

to control dust hazards is awareness.The Chemical Safety Board report1 

from the investigation of the tragic dustexplosion at CTA Acoustics in 2003 notedthat the dust explosion hazards associ-ated with phenolic resins were not welldescribed in the vendor’s MSDS. Oneof the key issues listed in the report is“Combustible Dust Hazard Awareness.”

Identify the hazards  Process safety hazards are identifiedand analyzed in the PHA. The dust hazardassessment is the analog for managementof dust hazards. The dust hazard assess-ment evaluates all five sides of the dustexplosion pentagon.

  1. Fuel: The dust hazard assessment begins with an inventory of all dust andmaterials that can become dust as a resultof the processing steps and includes all ofthe information obtained in understand-ing the process. From a list of all dusts,combustible dusts are identified along withtheir physical properties. Rolf K. Eckhoff 2 identified two characteristics of dust thatcontribute to its importance as a fuel in adust explosion — dust chemistry including

moisture, and particle size or specificsurface area. In many cases, sufficientdata are not readily available (such ason MSDS) so sampling and analysis isrequired.  • Ignition: Sources of ignitionare evaluated in the assessment and

the reduction of these sources is valu-able in reducing risk. However, dueto the nature of combustible dustclouds, complete elimination of igni-tion sources is difficult at best. Some

have used the phrase, “Ignition sources arefree,” meaning that ignition sources of suf-ficient energy are so prevalent that a dustexplosion mitigation strategy should neverrely solely on the elimination of ignitionsources.  • Oxygen: While reducing the oxygenconcentration below flammable limits canhelp reduce the risk, such a strategy isoften not practical. Many solids-handlingequipment and conveying systems areoperated in an air environment.

  • Suspension: The dust explosionrequires that sufficient fine particle sizedust be present and that it be well-dis- persed in a suspension of an oxidizer,typically air. The dust hazard assessment,therefore, evaluates the quantity of com- bustible dust that can become available foran explosion and the means for the dustto be lifted into a suspension. While thesuspension characteristic is not found onthe traditional flammability triangle, it caneasily be compared to having sufficientflammable material to be within flam-

mable limits.  • Confinement: The ignition of a dustcloud does not depend on confinement(other than assisting in building sufficientdust concentrations), but the resultingflame speed and pressure wave created bythe deflagration does. As with suspension,this is not unique to dust explosions.

Reduce the risk   The remaining PSM elements arefocused on reducing the risk associatedwith an identified hazard scenario. Forexample, mechanical integrity programs,operating procedures and managementof change all reduce the likelihood of an

event from occurring and occasionallycan reduce the magnitude of the hazard.Either result will reduce the risk. All ofthe risk reduction opportunities identi-fied in the PSM rule can be applied to adust explosion scenario to help minimizethe risk.  There is one noticeable difference,however, in the control of dust hazards.The difference is housekeeping. Dustaccumulations due to fugitive losses ofdust from the equipment are very dif-ficult to control at the source. Still, themost effective way to prevent a danger-ous accumulation of dust is to never losecontainment in the first place. For dustthat does leave the process, it is essential

that the equipment, including structuresand buildings, be kept clean and free ofaccumulated dust. Note that Eckhoff 3 hasillustrated that a dust accumulation ofonly 1 millimeter thick can result in a dustdispersion of 100 grams per meter cubedup to 5 meters high, sufficient to be in thecombustible range for some materials.  A word of caution regarding house-keeping — be careful to not create a bigger problem with the solution. For example,do not use compressed air to clear the dustaccumulations from equipment, thereby

creating the suspension of dust that you are trying taddition, as illustrated in thsion at West Pharmaceutithe location of the dust accunot be obvious, such as laysuspended ceiling.  As mentioned earlier, cotion sources will be part of thtion strategy. Ignition sourcemized through proper equiconsistent with the area eleccation, bonding and groundor insulating heated surface proper hot-work permitting,   Finally, the risk can b

through both active and psion mitigation. Effective minclude, for example, facilitygration venting, sprinkler scialized suppression systems

Conclusion  Risk management for explosions should be treatener similar to the strategy lOSHA PSM regulation. Thstanding the process, identifards, and protecting against facility can reduce the risk sion hazard to acceptable lev

For more information, Curtis at (281) 673-2963 o

tis@absconsulting.com.❑

1. “Investigation Report, Com Fire and Explosions (7 killedCTA Acoustics, Corbin, Kent2003. U.S. Chemical Safety

 No. 2003-09-I-KY, February2. “Dust Explosions in

 Industries,” third edition, Ro pp. 25 to 55.3. “CSB Investigation D

 Explosion at West PhServices,” published April 2

[COMPLIANCE TIPS]

Reducing the risk of dust explosion hazards

By: RICK R. CURTIS   Senior Risk/Reliability Engineer   ABS Consulting 

  Dust explosion pentagon. Source: U.S. Chemical Safety Board 

 Risk management for dust hazard

explosions should be treated

 similarly to the strategy in theOSHA PSM regulation.

Fuel Ignition

SuspensionConfine

Oxygen