How to Implement a Dust Hazard Analysis in Your Food Plant

Editor’s note: This is part two of a two-part series focused on dust hazard analysis. Part one, which appeared in the April/May issue, focused on the dust hazard analysis process. This article details how to put an analysis into practice at your food plant.

So, you’ve completed your dust hazard analysis (DHA). Now what? The DHA is just step one of your dust safety plan. Now it’s time to put the DHA recommendations into practice. That includes identifying and mitigating potential hazards and designing a dust collection system that complies with National Fire Protection Association (NFPA) guidelines.

Elements of a Dust Safety Plan

Creating or updating your dust safety plan will typically start with the dust hazard analysis. A new DHA should be completed every five years or when new processes, system changes, materials, or environmental hazards are introduced. It will typically include:

• Material characterization results (from specific dust testing or, in some cases, based on industry-standard values for food dust explosibility);
• Process characterization;
• Identification of specific hazards;
• Evaluation of existing safeguards;
• Mitigation recommendations; and
• A process for documentation and verification of hazard reduction activities.

Hazard Identification and Prioritization

The dust safety plan begins with understanding the specific hazards presented by your dust, your processes, and your environment. The dust hazard analysis should identify areas where hazards exist that could lead to a dust cloud explosion, including nodes where both oxygen and dust are present, potential ignition sources, (including heat sources from processes as well as static build-up, friction, or sparks from mechanical systems), and areas where dust tends to form clouds (e.g., dump points, batch mixers) and where dust clouds are enclosed (e.g., bins, silos, ductwork).

Hazard prioritization goes a step further. In this process, hazards are quantified and ranked using two metrics:

1. The likelihood that a combustion event could occur, given both the inherent hazards and the efficacy of any existing mitigations already in place; and
2. The potential severity of an explosion should one occur, given the characteristics of the dust (e.g., explosion indices), dust volume, physical facility layout, and the presence of other hazards, such as dust accumulation, that could fuel a dangerous secondary explosion.

Figure 1. Example hazard ranking analysis. Courtesy of RoboVent.

One simple way to prioritize hazards is to rank each issue on a scale of one to four for both likelihood and severity. Multiplying likelihood by severity gives you a numeric value for each hazard, from 1 to 16, with 1 being the lowest risk and 16 being the highest (see figure 1).

Each hazard is then assigned an overall risk level, which can be used to prioritize risk mitigation activities (see figure 2). Hazards with the highest risk levels should be addressed first; however, keep in mind that any issue that puts the facility out of compliance with Occupational Safety and Health Administration (OSHA) regulations and NFPA guidelines must be addressed in a timely manner, even if the overall risk level is determined to be low or moderate.

Figure 2. Example risk level prioritization chart. Courtesy of RoboVent.

Make Risk Mitigation Decisions

Once you have risks prioritized, you need to start making mitigation decisions. There is no single solution when it comes to combustible dust hazard mitigation. The tools and strategies used will depend on many factors and may include:

• Material substitution (though this is not always an option when dealing with food ingredients;
• Changes to processes (e.g., removing or shielding an ignition source, changing the design of conveyance systems or dump points to reduce cloud formation, etc.);
• Administrative standards and changes to worker behavior (e.g., using an NFPA-compliant vacuum system instead of brooms for housekeeping, limiting the number of people who have access to high-hazard areas, and providing worker training and education); and
• Engineering controls, including dust collection.

The explosion pentagon is a good place to start when evaluating potential risks and making mitigation decisions (see figure 3). All five elements of the pentagon must be present for an explosion to occur: a combustible dust, dispersion in a cloud, enclosure of the cloud, oxygen, and a source of ignition. Eliminating one or more of these elements will prevent an explosion from taking place.