Dust Hazard Analysis (DHA): How a Missed Static Spark Led to a Pharmaceutical Plant Explosion
- PSSI
- Apr 30
- 4 min read
Updated: May 1
Introduction: The Hidden
Danger of Static Sparks in Pharmaceutical Plants
A pharmaceutical plant’s newly commissioned reactor system, equipped with standard explosion protection systems, suffered a devastating dust explosion during routine powder handling. The cause of the explosion? A tiny electrostatic spark that went unnoticed in the Dust Hazard Analysis (DHA).This case study underscores the importance of a thorough DHA, following NFPA standards such as NFPA 660 (incorporating NFPA 652, NFPA 484 and others), to identify and mitigate risks. These standards help prevent accidents, reduce injuries, and minimize costly operational disruptions.
The Incident: A Recipe for Disaster
The incident occurred in a newly built manufacturing plant during a routine powder transfer operation. Here’s a breakdown of the reactor system and equipment involved:
Reactor: Constructed from carbon steel and lined with glass.
Charging Hopper: Made of stainless steel, unlined, used for transferring fine powder chemicals from Flexible Intermediate Bulk Containers (FIBCs).
Dust Collector & Nitrogen Purging System: Designed to remove excess air and reduce the oxygen concentration to prevent explosible dust-air mixtures.
During the operation, an operator cut open the FIBC liner to transfer powder into the reactor. Unseen by the operator, a static spark ignited the dust cloud, triggering a catastrophic explosion. The aftermath was extensive:
Charging hopper and reactor connections were blown out.
Windows shattered, and walls cracked.
Two employees suffered serious burns.
The FIBC and powder materials were burned, and the surrounding facility exhibited typical fuel-air explosion damage.
Conclusions: Analyzing the Root Cause of the Explosion
The explosion was most likely initiated by an electrostatic discharge, which could have occurred on the glass-lined and PTFE-lined pipes at the bottom of the charging hopper. The nitrogen-purged reactor-charging hopper system was designed to prevent oxygen from reaching the dust, but the dust collector fan induced an airflow much greater than the nitrogen supply. This imbalance caused a negative pressure in the charging hopper, leading to the opening of the pressure conservation valve. This allowed enough air to enter the hopper, creating an atmosphere capable of sustaining ignition and supporting dust cloud deflagration.
Further investigations revealed the following key points:
Electrical grounding issues: The shield element in the level probe was not grounded, potentially allowing sparks to ignite the suspended powder.
Construction materials: The use of insulating materials like glass and PTFE linings increased the risk of electrostatic discharges. These materials should be avoided when possible.
Root Cause: Gaps in the Dust Hazard Analysis (DHA)
A post-incident investigation revealed that the DHA had overlooked electrostatic discharge risks, despite having other explosion protection measures in place. Below are the key oversights:
Electrostatic Discharge Risks: These were not included in the Process Hazard Analysis (PHA).
Minimum Ignition Energy (MIE): The powder’s MIE was under 3 mJ, making it highly susceptible to ignition.
Charge Buildup: Electrostatic charge accumulation occurred during the gravity-fed powder transfer process.
Ignition Source: A spark from the chute likely triggered the ignition of the dust cloud.
Testing Results:
High resistivity (low conductivity)
Static charge accumulation
Ignition with minimal energy – very low MIE
Key Lessons to Prevent Dust Explosions
Conduct a Thorough Dust Hazard Analysis (DHA)
An effective DHA must identify all potential ignition sources, especially electrostatic hazards, during operations like powder transfer. NFPA 660 (Incorporating NFPA 652, NFPA 484 and others) require DHA updates every five years or after any major process change.
Test Your Powder's Combustible Dust and Electrostatic Properties
Before production begins, test materials for:
- Minimum Ignition Energy (MIE)
- Volume resistivity
- Explosion severity
These tests are essential to understanding the ignition risks posed by the materials in your process.
Reassess DHA After Equipment or Process Changes
Even small changes in equipment or processes can impact ignition risks. Always update your DHA accordingly. If something moves, mixes, or flows—check it for static hazards.
Final Takeaways: The Hidden Risk of Static Electricity
Static electricity is often underestimated, yet it is one of the leading ignition sources for combustible dust explosions. If your facility hasn’t fully evaluated electrostatic risks, it’s time to take action. At PSSI, we specialize in:
- Assessing combustible dust hazards
- Analyzing electrostatic ignition risks
- Planning effective explosion prevention strategies
Related Links
- NFPA 660, Standard for Combustible Dusts and Particulate Solids (2025)
- What is Minimum Ignition Energy (MIE)
- PSSI Dust Safety Services
Have You Updated Your DHA Recently?
When was your last Dust Hazard Analysis performed? Let us know in the comments or reach out for a consultation. We’d love to help you improve your facility's safety.
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For more information about practical and effective control of static electricity, dust explosion and other related safety issues or for a complementary discussion with one of our electrostatic specialists, please click the “Static Electricity" page of this website or give us a call on 609 240 7545.
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