A Tiny Electrostatic Spark Ignited a Dust Explosion in a New Pharmaceutical Plant

A chemical reaction process in a newly commissioned pharmaceutical plant began with loading a combustible powder in a supersack (FIBC) into a glass-lined reactor through a closed hopper system as shown in Figure 1. In the middle of supersack unloading, a dust explosion occurred, causing two secondary explosions. The explosions damaged the hopper, broke the window glasses, and damaged the building walls. The two employees who were conducting the operation suffered severe burn injuries.

Right after the site was secured, our team conducted site survey and inspection, evaluated materials involved, process and plant, performed onsite electrostatic measurements, and interviewed plant personnel. We found that the plant had been provided with the following safety measures to prevent dust explosions:

• The reactor and the hopper were protected with nitrogen inerting;

• A dust collector was installed to control dust concentrations in the hopper and fugitive dusts;

• The plant was kept clean with excellent housekeeping;

• All equipment was grounded adequately;

• Hazardous areas in the plant were adequately classified according to the National Electrical Code (NEC/NFPA 70) to prevent electrical ignition hazards; and

• A HAZOP (PHA), which includes dust hazard assessment (DHA), had been conducted.

Why Did This Explosion Happen in This New & Protected Plant?

It was very puzzling that this new, clean and explosion-protected plant, provided with several safety measures, still had a dust explosion. Our investigation revealed several failures in the design of the powder handling system and one of them was a failure to prevent electrostatic sparks.

Firstly, the HAZOP/PHA failed to grasp the gravity of the combustible dust hazards of the powder and the potential electrostatic ignition hazards of the powder itself and the materials of construction for the reactor and pipes. As a result, the company only recognized that the powder poses a dust explosion hazard but stopped making further efforts to determine the ignition sensitivity to electrostatic hazards.

Our tests revealed that the powder is high insulating, capable of building high levels of electrostatic charge in the powder loading process, and needs very small amount of spark energy to ignite (<3 mJ). Our electrostatic reconstructions test results showed that the gravity discharge chute would have been the ignition source due to the high electric resistivity and electrostatic chargeability.

The pile of powder collected in the glass-lined reactor could also have been another potential ignition source that could have ignited the dust cloud in the reactor resulting in more extensive damage and personal injuries. Fortunately, the inerting of the reactor, although not fully accomplished, would have prevented an ignition of the dust in the reactor.

How to Effectively Control of Combustible Dust Hazard and Electrostatic Hazards?

Firstly, a Dust Hazard Analysis (DHA)/PHA should include systematic review and assessment of all potential ignition sources including electrostatic ignition sources.

Secondly, since fire and explosion hazards and risks are determined by many factors including the materials' properties, processes, process equipment, process conditions, equipment layout, facility designs, and the existing preventive and protective measures, whenever there is a change made in a plant, the impact on the fire and explosion hazards should be reviewed and assessed. This is why NFPA 652 requires that the DHA be reviewed and updated every 5 years or after a major change is made.

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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.