Combustible Dust Hazard Analysis (DHA): A Step-by-Step Guide to Ensuring Safety
Step 1: Gather Essential Documentation
Step 2: Conduct Field Verification
Step 3: Assemble Your DHA Team
Step 4: Identify Hazards and Evaluate Compliance
Step 5: Prioritize Identified Hazards
Step 6: Document Your Findings
Step 7: Regularly Review and Update
Simply completing a combustible dust hazard analysis (DHA) won’t automatically make your facility safer. Meaningful safety improvements happen through appropriate follow-up actions (as detailed in steps 5 through 7) or hiring a dust hazard analysis consultant.
The process described below assumes your facility already handles Industrial dust hazard analysis through manufacturing, processing, or other activities. If you aren’t sure if your dust is combustible, please see the “Burning rate test page?” section of our website to learn more details. Our goal is to provided up to date and reliable information.
Here are the key steps for conducting an effective DHA:
Step 1: Gather Essential Documentation (Combustible dust assessment)
Start by collecting all relevant drawings and documents that describe your processes, equipment, operating parameters, and any existing hazards. Examples include:
- Process flow diagrams (PFDs)
- Piping and instrumentation diagrams (P&IDs)
- Mass and energy balances
- General arrangement drawings
- Building plans
- Equipment manufacturer specifications (drawings, data sheets, manuals)
- Electrical hazard classification drawings
Older facilities might present challenges in obtaining all these documents. In such cases, a thorough field investigation becomes necessary to adequately document the processes, equipment, and facility for the analysis. Interviews with plant operations staff can often provide undocumented process data.
Documenting and understanding the materials used in each process stage and their properties is also essential. Many dust hazard analysis consultants consider processes alter a material’s characteristics, such as particle size, particle size distribution, and moisture content, all of which significantly impact the dust’s hazard level. If dust properties have been tested (e.g., , , minimum explosive concentration (MEC)), obtain and verify the test reports to ensure they represent the various stages where properties might change.
Finally, gather the applicable NFPA standards. NFPA 652 provides guidance on industry-specific or commodity-specific standards relevant to your facility. While other standards may apply, NFPA 68, Standard on Explosion Protection by Deflagration Venting, and NFPA 69, Standard on Explosion Prevention Systems, are likely necessary references for any facility.
Step 2: Conduct Field Verification
Even when facility-specific documentation exists, it’s often outdated or incomplete. The older the facility and its dust hazard analysis documentation, the greater the chance of undocumented changes. Perform due diligence to verify the information that will form the basis of your DHA.
When existing documentation is limited, you might better term this step a “Field Survey.” Thorough documentation of larger, older facilities may require significant effort to support a comprehensive DHA. This presents an excellent opportunity for facilities lacking up-to-date PFDs to revise their drawings to reflect the current plant configuration.
Step 3: Assemble Your DHA Team
NFPA 652 recommends (though doesn’t mandate) that a team perform a DHA and requires that a qualified individual lead it (Giusto, 2019a). Taking a team approach allows plant engineers, EHS (Environmental, Health, and Safety) personnel, and plant management to contribute their unique perspectives. Include maintenance and operations personnel, as their hands-on experience often provides valuable insights into potential combustible dust hazards.
The perspective of a consultant experienced in the DHA process can also prove invaluable. An external expert with experience across various industries might identify hazards and suggest solutions that internal team members might overlook. As the saying goes, “You can’t read the label from inside the jar.”
Step 4: Identify Hazards and Evaluate Compliance
This step is the core of the DHA and the primary reason NFPA 652 mandates the process. Many combustible dust incidents have occurred because of unrecognized hazards. This step involves systematically reviewing your process and facility to identify potential hazards. The team can use various approaches and formats for this review, but the objective is to consider every point in the process, identify hazards, and determine the necessary measures to minimize risks.
Remember the fire triangle and explosion pentagon during this stage (Giusto, 2019a). However, since air is usually the oxidizer, and you wouldn’t conduct a DHA without combustible dust (fuel), the analysis often focuses on dust quantities or concentrations and potential ignition sources.
For each process step and facility area, consider:
- Is there, or could there be, enough dust to create a combustible atmosphere?
- Are there, or could there be, ways to disperse dust into a cloud?
- Are there, or could there be, any ignition sources present?
It’s equally important to identify any existing protective measures. If hazards already have NFPA-compliant protection, no further action is immediately needed. Documenting these measures alongside the hazards is crucial. Also, evaluate installed measures to confirm compliance with NFPA standards.
For example, one facility had an explosion vent on an indoor dust collector that vented through the roof. While seemingly a good safety measure, closer inspection revealed an improper weather cover over the vent duct, and the duct wasn’t sized correctly per NFPA 68. These issues could have prevented the vent from functioning properly during an explosion. Ultimately, the team determined that the roofline was too far from the dust collector for a compliant vent duct, and they installed a flame-arresting vent with particulate retention instead.
Step 5: Prioritize Identified Hazards
Once the team identifies hazards, they must prioritize them to address the highest-risk hazards first. Similar to Step 4, various methods can be used, but a risk matrix is commonly employed to rank hazards based on the anticipated likelihood of an event and its potential severity. Some hazards may require immediate action, while others can be scheduled for future remediation.
Step 6: Document Your Findings
NFPA 652 mandates the documentation of DHA results. Complete and thorough documentation is vital for two main reasons:
First, authorities having jurisdiction (AHJs), such as local fire marshals or OSHA representatives, may request to review the DHA. A comprehensive and well-organized report demonstrates compliance with relevant codes and standards or shows that identified areas needing attention have a plan for resolution.
Second, the DHA report serves as a crucial reference for management of change as processes are modified, and your facility undergoes upgrades or expansions.
Step 7: Regularly Review and Update
In facilities where combustible dust hazards haven’t previously received adequate attention, completing a DHA should initiate a shift from reactive compliance to proactive hazard management. You need to revisit and update the DHA whenever your facility undergoes changes. This includes modifications to existing process operating parameters, the introduction of new or different materials, or the installation of new equipment or processes. In some facilities, this might occur several times a year, while others may experience longer periods without significant changes. To prevent complacency and the cumulative effects of subtle changes, NFPA 652 Section 7.1.4 requires the DHA to be reviewed and updated at least every five years.
In Conclusion
For facilities handling combustible dust, a DHA is essential for ensuring the safety of both the facility and its personnel. This is why NFPA 652 required the completion of a DHA by September 7, 2020. This information aims to help readers understand the necessary steps for conducting a DHA and emphasizes the value of this process beyond mere regulatory compliance.
