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Combustible Dust – Understanding NFPA 654

| By Chemical Engineering

Combustible dust is a critical concern for any industry that processes and conveys dry bulk materials in their production facility. Changes in regulations have brought this issue into even greater focus. Nol-Tec Systems’ design teams are experts in developing systems hard-to-handle materials, to minimize the production of dust and the possibilities of combustion.

The National Fire Protection Association (NFPA) has issued stricter standards for safety measures used to prevent and mitigate explosions and fires in facilities where a combustible mix of dust/air could be present. Some of these changes include particle size (material less than 40 mesh) and the inclusion of more organic materials.

Combustible Dust Pentagon

Removal of any one element can prevent explosions.

Also, the United States has fully adopted the Globally Harmonized System for the Labeling and Classification of Chemicals (GHS), which has new standards for combustible dust. These standards are incorporated into the NFPA recommendations. These changes mean the reach of the codes has changed substantially.

There are several NFPA codes that pertain to combustible dust, but it is the intent to have standards address consistently across industries and materials. Nol-Tec has broad experience in conveying materials in all of these categories.

  • NFPA 652 – general regulation which directs users to the more specific industry and commodity specific standards
  • NFPA 654 – manufacturing, processing, and handling – broadest regulation and the base for the others
  • NFPA 61 – agricultural and food processing (organic dusts)
  • NFPA 484 – combustible metals
  • NFPA 655 – sulphur
  • NFPA 664 – wood processing and woodworking

Many chemicals not previously classified as hazardous are now designated as combustible dust explosion hazards. The Kst (dust deflagration index) of a myriad of powders have been updated.

The Kst value indicates how easily a material or mixture ignites, what the speed of fire/explosion propagation is, and the amount of energy released in the explosion. It measures “relative explosion severity compared to other dusts” (OSHA’s Hazard Communication Guidance for Combustible Dusts, OSHA 3371-08 2009). These are all indicators of the severity of a dust explosion with a given material. In fact, so many dusts are classified combustible that the focus is now on that severity potential and how to mitigate it.

High Profile Combustible Dust Explosions Lead to Stricter OSHA Enforcement
In late 2014, the Occupational Safety and Health Administration (OSHA) received a mandate to fully enforce these updated NFPA standards, covering hundreds of chemicals, organic materials, metals, and powders. This stricter enforcement has been, in no small part, due to several high-profile combustible dust explosions.

The United States Chemical Safety Board (CSB) investigates these accidents and issues final reports and recommendations for any facility to reopen and continue their work with combustible dust. Their findings can also be very informative for other similar facilities working to minimize the explosion potential in their own plants. An excellent example of this reporting can be found at, along with video exemplifying how dust combusts and the damage it can inflict on a facility and its staff.

Along with these CSB recommendations, OSHA utilizes NFPA 654 to inform more site inspections for violations such as poor housekeeping, inadequate communication of the hazards posed by a material, and insufficient hazard control.

Hazard control has typically been focused on two areas. The first is facility housekeeping and containment of the materials. Nol-Tec is an expert in handling difficult bulk materials – those that are fragile, friable, or abrasive. We know how to design a system that will minimize the breakage on your materials. Less breakage means less dust which means minimized risk for combustible dust explosion. Also, the less dust that escapes the conveying process, the lower the risk of explosions due to accumulations of dust in the facility. Nol-Tec Systems’ dense and dilute phase pneumatic conveying designs are fully enclosed and are reliable tools for the maintenance of a clean facility.

Explosion Mitigation: Preventing Combustible Dust Explosion
The second area of focus has been explosion mitigation. This is generally accomplished through the use of explosion panels, venting systems, and/or explosion suppression systems. Panels and venting can help control the release of energy in case of an explosion, which can minimize damage to the plant and increase personal safety. There is, however, damage to the processing system itself, as well as loss of the dry bulk material that exploded and burned in that contained circumstance.

Suppression systems involve the use of a suppressing chemical being released into the convey system when potential explosive conditions are detected by a pre-programmed safety system. These kinds of systems will stop the explosion, but the material and the convey lines are contaminated. The material will have to be discarded and the convey lines scrubbed, costing time and money.

Nol-Tec and Air Products and Chemicals have partnered on research for a system that would, in fact, prevent combustible dust explosions through the use of inert gases as the conveying air, rather than oxygen.  Removing the oxygen from a dust/air mixture means no explosion is possible, for the vast majority of compounds. They have co-authored a paper in the March 2015 issue of Chemical Engineering. Further details on this research and its practicality for conveying combustible dust materials can be found here.

Contact Nol-Tec for Help with Dust Explosion Mitigation
Nol-Tec’s test lab and design staff are actively implementing these new NFPA 654 and GHS standards in our own facility and incorporating them into our design work. With over 30 years in the industry, Nol-Tec is in an exceptional position to understand the broad impact on our customers’ businesses. We have been updating our designs and recommendations to meet the challenges of these new regulations. Contact us today at to learn more about how can partner with you to respond to the changing regulatory climate.