Is the IH Respiratory Hazard also an Explosion Risk?
By: Mark Yukich & Ashok Ghose Dastidar, Contributors
As a professional, the importance of identifying respirable industrial hygiene hazards and taking the steps necessary in reducing the amount of exposure to encourage a safe atmosphere for workers is vitally important. However, when tasked with reducing respirable dust hazards within a facility’s process, it is recommended to identify the potential explosibility and/or combustibility of the dust generated within the process line. Our aim is to provide a brief overview of questions to consider when assisting a facility with respirable dust hazards and how to determine the potential for combustible dust risks.
When you are conducting a safety assessment at a facility where dust is airborne within the process area, the question that should be asked of the facility operator is: “Have you ever had this dust tested for explosibility or combustibility?” The dust generated in many different processes can be found to be explosible and/or combustible, but the first step is to test a representative sample from the process by running the Explosibility and Combustible Screening Tests. These tests will provide a “yes” or “no” result for each test result.
NFPA 652 Standard on the Fundamentals of Combustible Dust mandates that, if a facility has a combustible and/or explosible dust, the facility operator must complete a Dust Hazards Analysis (DHA) of the process are that handles these materials.
There is a difference between explosible and combustible. The explosibility screening test determines if the material is explosive within an airborne dust cloud. Any pressure rise greater than 1 bar (approximately 15psi gauge) is deemed an explosible material. The combustibility screening test determines if the material will propagate a flame while in a pile or layer. A material can be explosible and may not be combustible. For example, sugar is explosible in a dust cloud, but is not combustible. When tested in a layer, the material will melt, where there may be a hazard of a subsequent pool fire from the melted sugar—which should also be evaluated.
Now that it has been determined the sample is either explosible and/or combustible, NFPA 652 requires the DHA be completed. The DHA is a risk-identification exercise, performed by an experienced engineer, of the process areas where these reactive materials are generated and/or handled. The result will provide recommendations to help reduce risk within the current operation. Prior to the site visit taking place, obtaining the explosion and combustion characteristics that will demonstrate how the material reacts under different hazard conditions will prove to be the most efficient use of your time.
Earlier, we talked about the screening tests giving a “yes” or “no” answer, but there are other tests commonly referred to in NFPA codes that would be helpful to have on hand. Some of those data points that are key to developing a mitigation strategy are found below:
Explosion Severity Test (KSt Pmax) – This test is used to determine the appropriate size/strength of the dust collector that supports the process line and what type of explosion protection is required. This explosibility test demonstrates how strong and how fast of a reaction can occur within a dust cloud when initiated by an ignition source.
Minimum Ignition Energy (MIE) – This test demonstrates the minimum amount of ignition energy needed for a reaction to occur. The result of this test is measured in the minimum amount of energy that is measured in millijoules (mJ). As a point of comparison, when you receive a shock when going to touch a doorknob, this is a spark that is generating about 30-40mJ of energy. In fact, there are some materials that can react with as little as 1mJ. Part of the impetus of a DHA is identifying potential ignition sources. Understanding the MIE will go a long way in guiding the process of identifying the hazards that may be present due to the presence of an ignition source.
Minimum Explosible Concentration (MEC) – This test will illustrate the level of dust concentration needed within a dust cloud to have an explosible reaction. There are mitigation strategies to keep airborne combustible dust concentrations below the MEC value, so as to take steps necessary to reduce risk within the operation.
On-Site Analysis & Management
Once you have the test data compiled, schedule the on-site Dust Hazards Analysis (DHA) to be completed with the assistance of a qualified engineer to guide the risk-identification process by following applicable NFPA codes, specifically NFPA 652 and NFPA 70 National Electrical Code. The DHA is a hazard-identification assessment with recommendations in reducing risk within the operation. The recommendations could include any need for explosion/deflagration protection, grounding and bonding, ignition source control, electrical area classification and training personnel to identify hazards, just to name a few items.
When the recommendations are put into place, it is important to develop a Combustible Dust Management Program (CDMP) to ensure that the key findings uncovered in the safety audit are understood and implemented. The CDMP will have to address a regular maintenance schedule to confirm that the applied safety measures are properly maintained. Also, there needs to be key personnel identified that will help keep the facility on track with these safety strategies. Part of this will include a “management of change” program to ensure the safety steps taken are part of a group collective mission, rather than left to one individual, and that modifications to equipment and processes do not compromise the designed safety profile.
Overall, the practice of good housekeeping on a regular schedule is a fundamental recommendation towards reducing the risks related to combustible and explosible dust within any process. As an IH professional, you understand how important it is to reduce the airborne hazards present, so you play a key role in the primary recommendation that is found for any facility handling combustible dust. Airborne dust found to be explosive and/or combustible will be recognized as a primary fuel source, just like any other flammable fuel like acetone or gasoline.
Whenever you find yourself within a facility focusing on the IH hazards, take a moment to ask them the question, “Have you ever tested your dust for explosibility and combustibility?” Every facility operator has the duty to know what combustible dust risk, if any, is present to protect the safety of their people and facility. Fauske & Associates, LLC can assist with all facets of the testing and on-site process safety support.