How to Optimize Dust Testing
Most pharmaceutical owners/operators know that potentially combustible dust must be tested. Combustible dust testing is required by the NFPA to determine whether it’s combustible (can burn) or explosible (rapid increase in volume creating a subsonic shock wave). This can be done by researching published data for common materials or having a dust sample from the facility tested.
However, once a dust is known to be explosible, owners/operators must test further to assess the hazard and specify explosion protection equipment.
Clients often ask me which tests they should request from a lab, and the short answer would be: Run them all. However, engineering is about optimization and performing tasks as efficiently as situational constraints allow. You might not need to run them at all. While several published sources provide properties of well-known excipients such as sugar, gelatin and corn starch, active pharmaceutical ingredients (API) present a different challenge. Since there often is no published data for these powdered compounds, they need to be tested for explosivity. And what about materials that are in-process?
For example, could dust from a natural organic material mixed with dust from a synthetic organic or metallic material be considered “similar enough” to already-tabulated combustibility property values? Is that data accurate enough to determine the size of that explosion vent panel? When it comes to personal safety and asset protection, I would say no. It’s crucial to be as accurate about hazardous materials as possible. This also means using “fresh” dust from a process, not dust collected off the floor, since it might be contaminated with other particles.
Know the Types of Combustible Dust
When it comes to testing, there is no one-size-fits-all solution. There will be circumstances in which owners/operators need to know multiple explosibility properties, and others that are not necessary to ensure safety. . Dust testing encompasses many acronyms and abbreviations for combustibility properties, and nearly all are associated with a separate lab test. Below, I break down the types of dust testing and which ones, in my experience, leverage resources best:
- Kst (Explosion Severity): Always. It’s the standard index to compare dust explosibility.
- Pmax (Maximum Explosion Pressure): Always. It’s crucial to know how much pressure an explosion can generate, then engineers can specify an explosion vent.
- LIT or Tc (Layer Ignition Temperature): Always. The temperature at which a dust layer begins to smolder is important because it creates an ignition source for fire or explosion. Hot surfaces that could accumulate dust need to be kept below the LIT, which includes: light fixtures and bearings on rotating equipment. Lights can be specified with acceptable temperature ratings, while bearings can be monitored to ensure they stay below the LIT.
- MIE (Minimum Ignition Energy): Usually. If personnel handle dust in flexible intermediate bulk containers (FIBCs, commonly called bulk bags or super sacks), MIE helps specify the type of FIBC material that can be safely used. Distinct types of FIBC material are required for materials with low MIE. A low MIE coupled with a material that is a good insulator may result in NFPA code requirements that limits the container transfer rate, which can them limit choices for conveying equipment and operating procedures for that equipment.
- MEC (Minimum Explosion Concentration): Usually. This data helps define whether a dust deflagration hazard may be present. For example, dust within collection ducting often has a concentration of less than 25 percent of the MEC. Those ducts would not be likely locations for a deflagration to start. Those ducts would still allow a deflagration flame front to travel from one piece of dust handling equipment to another. Meaning, there would still be a need to place protection on the ducts.
- LOC (Limiting Oxygen Concentration): Sometimes. Dust deflagration hazards are rarely controlled by limiting oxygen concentration. An inert gas blanket requires sensitive pressure and vacuum relief devices that can be affected by a dusty environment.
- CIT or Tc (Cloud Ignition Temperature): Sometimes. The LIT is typically lower than the CIT, and since the LIT is more restrictive, the CIT is not necessary. Also, CIT is frequently greater than 300º C (572º F). A surface that hot may not be present in many facilities, unless they have fuel-fired equipment. CIT can be important when it is possible to have hot surfaces that will not collect a dust layer (i.e., vertical surfaces), but can become ignition sources for suddenly released dust clouds.
Remember, no matter which tests pharmaceutical owners/operators decide to perform, it’s imperative that unidentified dust is tested and proper procedures are put in place to mitigate risk to personnel and assets.
If combustible dust and process engineering services are needed at your pharmaceutical plant, don’t hesitate to reach out to EAD at firstname.lastname@example.org or at 402.884.8650. You can also follow us on LinkedIn to learn more about our in-plant expertise.