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NFPA 654 Combustible Dust Standard—2011 Edition

By W. Jon Wallace, CSP, MBA

Several recent combustible dust explosions, including the February 2008 incident at Imperial Sugar refinery resulting in 14 fatalities, has greatly increased industry awareness of the hazards of combustible dust. NFPA 654, Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids is the defacto dust explosion prevention standard. NFPA 654 applies to non-specific combustible dusts, including plastics, pharmaceuticals, textile papers, and paper products. The 2006 edition of NFPA 654 provides a template to address combustible dust hazard identification and control.

NFPA 654 is presently being revised and will be issued as the 2011 edition. The code committee finalized proposed changes to the definition of combustible dust as well as requirements related to hazard assessment, explosion isolation, fugitive dust control and housekeeping, control of ignition hazards, and contractors.

Combustible dust: The first step in hazard identification is recognition of what materials constitute combustible dusts. NFPA 654 currently includes combustible particulate solid to emphasize that larger solid particles can be broken down into finely divided solid form that may become combustible. For a combustible dust explosion to occur the dust must be suspended in air at the correct concentration with an ignition source, and where confinement occurs – such as a building, structure, or process equipment. The NFPA 654 committee proposes to revise the definition of a combustible dust as follows: “Combustible dust is a combustible particulate solid that presents a fire or explosion hazard when suspended in air or the process-specific oxidizing medium over a range of concentrations, regardless of particle size or shape.”

Housekeeping: Combustible dust explosion investigations conducted by the Chemical Safety Board (CSB) as well as OSHA indicate inadequate housekeeping as a contributing factor in several incidents. Typically, the secondary explosion results in the most damage. The initial explosion causes combustible dust to become airborne which is often ignited by the initial ignition source. Proper housekeeping is critical to reduce the potential and severity of a secondary explosion.  The proposed revision to NFPA 654 requires implementation of a planned inspection process to determine facility dust accumulation rates and determine housekeeping frequency necessary to maintain accumulations below acceptable levels.

Another proposed change clarifies the hierarchy to be utilized during cleaning. Investigation findings indicate improper cleaning methods may be more dangerous than no cleaning. The committee states vacuum cleaning is the preferred method for cleaning, followed by sweeping or water wash down. Blow down using compressed air or steam is allowed only after other methods have been utilized or other methods are considered more hazardous. Use of blow down method requires a restriction on air/steam pressure and use of protected electrical equipment.

Contractors: A new selection on contractors and subcontractors has been added requiring contractors to possess appropriate credentials documenting their qualifications and to be specifically trained in the installation, testing, and maintenance of systems and equipment they are interacting with. Also, contractors must be trained on facility safe work practices.

The release of the 2011 Edition of NFPA 654 is expected during the middle of 2010.

If you have any questions concerning this article or other safety issues, please contact W. Jon Wallace at 919.933.5548 or by