Combustible Dust Standards for Dust Collection Systems

June 23, 2015

4 Min Read
Combustible Dust Standards for Dust Collection Systems

The release of NFPA 652: Standard on Fundamentals of Combustible Dusts will have a direct impact on plant operations that utilize dust collectors. The new standard is designed to provide the basic principles and requirements for handling combustible dusts. Ultimately, NFPA 652 is meant to provide you with a three step approach to identify your combustible dust hazard, analyze your dust hazard, and manage your dust hazard. This process becomes critical for facilities operating dust collection equipment. Dust collection systems for combustible dust represent a significant increase in deflagration risk compared to most process equipment.  

Hazard Identification
The first step in the process is to determine if your dust is combustible. Dust samples can be tested by certified laboratories or you can use historical, published information. Dust testing can determine a variety of different parameters including deflagration index (Kst), maximum deflagration pressure (Pmax), minimum ignition energy (MIE), and maximum explosive concentration (MEC). When using historical or published data it is important to verify if the data represents the materials being handled in your process. Additional information can be found in NFPA 652 regarding the use of published data for your dust samples. Once you identify the parameters of the dust being collected in your dust collector, you can begin to analyze your dust hazard.

Dust Hazard Analysis
A Dust Hazard Analysis (DHA) is a focused analysis on all areas of a process related to a combustible dust hazard. A DHA will now be required under NFPA 652 for all facilities that handle combustible dusts. The goal of a DHA is to identify and evaluate the process, facility, scenarios, operations, and safeguards, in regards to a combustible dust hazard. This analysis needs to be conducted by a qualified person and documented. NFPA 652 provides a guideline for how to conduct a DHA and even provides a step by step example in the appendix.
    
Dust collection systems should definitely be included in a DHA.  Dust collectors have an inherent risk when handling combustible dust. This risk is due to the design and operational characteristics of a dust collection system. Dust collectors operate with four of the five elements needed for an explosion - combustible dust, oxygen, a suspended dust cloud, and a confined area. The element not regularly occurring in a dust collector is an ignition source. Analyzing possible ignition sources is critical in DHA for a dust collector. Another part of the DHA process, is to analyze if the dust collection system is properly designed and located. Proper dust collection designs require minimum air volume flows and velocities to be maintained. Additional concerns should be the dust collector maintenance and the presence of prevention and mitigation safeguards.

Hazard Management
Managing the hazards identified in your DHA is the final step in providing a safe combustible dust handling process. Hazard management will include risk analysis, operation procedures, equipment design, housekeeping, ignition source control, PPE requirements, and mitigation safeguards.
    
Implementing a management of change (MOC) program for your dust collection system is important to avoid the introduction of hazards. Establishing procedures for hot work will limit the introduction of potential ignition sources. Developing preventative maintenance processes for your dust collection system will help keep your dust collector operating as designed.
    
Additional safeguards may need to be implemented to prevent or mitigate the effects of a dust explosion.
  
Prevention techniques for dust collection systems include:
•    Bonding and grounding
•    Hot-particle detection
•    Inerting
•    Process interlocks

Mitigation techniques for dust collection systems include:
•    Explosion venting
•    Flameless venting
•    Chemical suppression
•    Isolation devices – valves or chemical
•    Containment
•    Fire protection systems

Dust collectors have been a well-documented source of dust explosions in a variety of process industries. Designing and operating your dust collection system to the latest combustible dust standards is critical for operating safe facility.
 
Jason Krbec is the sales engineering manager for CV Technology. He is a PE and has a BS in mechanical engineering from the University of Florida. He is a member of the technical committees for NFPA Standards 68, 69, 652, 654, and 655.

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