Combustible Dust Strategies Meet OSHA Requirements, Maintain Productivity: Q&A Session

Webcast Q&A session with presenter Kirt Boston, Global Manager of Torit Technology, Donaldson Group

  1. Q: I agree point-of-use collectors are cost-effective, however in many cases there are space considerations. Any suggestions on managing space for dust collection/handling?
    • A: Applying dust collection close to the point where dust is generated offers many advantages and will often provide operational savings.  In many instances collectors can be readily relocated close to the dust generation point, but in some instances it is necessary to have very small collectors that physically will fit where the dust is being generated.

      There are now a variety of technologies and products including Donaldson PowerCore Collectors which offer the smaller more compact collector size needed for those locations where the point-of-use approach has limited space.  These smaller collectors facilitate the desire to apply collectors close to the point of dust generation.

      “Cost Advantages of Point-Of-Use Collection in Dump Pit Applications,” and “An Optimized Approach to Dust Control in Grain Elevators and Terminals” are two white papers available on the DonaldsonTorit.com website illustrating how Power Core technology can be leveraged in Point-of-Use collection strategies.

      Contact your local Donaldson Torit representative for additional information.

  2. Q: What methods/equipment is best for collecting aluminum dust?
    • A: Currently OSHA does not have a federal standard to reference on combustible dust but OSHA inspectors have been instructed to consider NFPA standards as well recognized guides on feasible mitigation strategies for combustible dusts.

      NFPA 484 Chapter 8 contains specific language related to combustible dust hazards in machining, fabrication, and finishing of aluminum, including cautions on thermite reactions when aluminum fines are mixed with metal oxides such as iron oxide. [NFPA 484,8.1.4.3, 2012 Edition]

      Mitigation strategy considerations for metal dusts should include the possibility of incompatible materials becoming mixed in a dust collection system.

  3. Q: Are dust collection units a serious concern?
    • A: The presence of a combustible dust in a process creates a serious concern which should be reviewed and evaluated in a process hazard assessment of the process.

      As a component in a filtration system, dust collectors have been identified in several studies as a viable location for combustion events.  As noted during the Webinar discussion, this pattern can be partially explained by the combination of conditions which exist within dust collectors, and particularly within continuous duty media collectors such as baghouse or cartridge collectors.

      Combustible dust suspended in an oxidizing gas (assuming air as the conveying gas) inside the enclosed housing of a collector represent four of the five conditions necessary for a combustion event. 

      The introduction of an ignition source into the collector then completes the conditions for a fire, and if dust concentrations are high enough when the ignition source is introduced an explosion could occur.

      Fortunately, the concentration of dust in typical dust control systems is often well below the concentration necessary for a flame front to propagate through the dust cloud.  As dust accumulates on filter media in the collector during operation some form of cleaning system is often used to periodically purge accumulated dust from the filters.  During purging the concentrations of dust in the volume around the filter increases and may achieve or exceed the minimum explosible concentration necessary for an event.  If an ignition source is also present a deflagration / explosion event could occur.

  4. Q: Do the new regulations mean existing customers with blast machines and dust collectors have to modify their installation to include fire protection controls?
    • A: Combustible dusts in a process should be considered as a possible risk in a process hazard assessment of the process.  And the outcome of a risk assessment of the process should provide the basis for any decisions on mitigation requirements.

      It is worth noting the National Fire Protection Association Standards do allow an Authority Having Jurisdiction to apply provisions of standards retroactively if the situation is deemed to present an unacceptable degree of risk.

  5. Q: How do you determine the required dust collection strategy for a new process in which you cannot yet collect dust samples for lab testing (proactively specify a system)?
    • A: Determining the conditions in a new process can be challenging and predicting the combustible dust challenges are no exception.

      Practices outlined in NFPA standards promote the use of process hazard analysis as the basis for mitigation strategy development.  In situations where specific details are not available, such as the properties of potentially combustible dusts which have not yet been produced, the standards permit sizing to be developed from properties of materials expected to be fundamentally similar, but the standards also require confirmation once the actual materials involved become available.  [NFPA68, 8.1.2 - 2013 Edition]

  6. Q: Info regarding indoor dust collector requirements and explosion control/suppression options.
    • A: NFPA and the International Mechanical Codes each contain language on specific requirements for collectors intended to be installed indoors.

      A thorough review of all applicable standards should be done by the process owner as requirements may vary for specific dusts, collector styles, or jurisdictions.

  7. Q: Ductwork design
    • A: Principles for effective industrial ventilation design topics from hood design to fan and collector selection are well documented in a variety of manuals and texts.

      A frequently referenced standard on this topic is published by the American Conference of Governmental Industrial Hygienists [ACGIH], Industrial Ventilation – A Manual of Recommended Practice for Design, 28th Edition.  This publication includes guidance on multiple topics around industrial ventilation system design.

  8. Q: How to accurately assess the necessary fan size and CFM needed in our dust collection upgrades.
    • A: Local exhaust ventilation when properly designed and operated has been shown to be very effective in containing and capturing dust generated in processes.

      Specific guidance on the design of local exhaust ventilation hoods and duct systems can be found in the publication Industrial Ventilation – A Manual of Recommended Practice for Design, 28th Edition published by the ACGIH.

  9. Q: On Slide 39, Kirt discussed air returned to a facility from a dust collection system. Is it possible to safely return air to a facility when collecting particles/fumes from laser cutting of metals (or specific metals).
    • A: As was mentioned in the presentation, decisions on returning of filtered air to an occupied space should be based on the outcome of a thorough process hazard analysis.

      NFPA Standards establish several different air quality requirements for air being returned to a facility, depending on the dust, the process, and the industry involved.

      In addition the NFPA standards generally require provisions be in place to prevent the return of flames, smoke, or pressure back into the facility.