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July 2020 / 31 protective equipment (PPE) requirements, house- keeping schedules, thresholds and methods, hot work requirements, training, contractors, incident investiga- tion as well as others. Method of analysis There isn't a defined or set method to use to complete a DHA. However, there are methods that have proven to be effective, thorough, and applicable to all types of combustible compliance issues. Typically, methods used to complete a PHA will work with a DHA, but the DHA only focuses on combustible dust issues. Some people in the powder and bulk materials industry have successfully used a checklist–what-if combination for hazard determination and a risk assessment matrix for determining the current risk level and what must be done to reduce the risk to an acceptable level. A risk assessment matrix, as shown in Figures 1 and 2, is a valuable tool that's allowed per NFPA 652, Chapter 9, "Management Systems." The remainder of this article will provide a partial example of a typical method for a DHA using the checklist–what-if method. The key is to provide a checklist that covers the equipment and system items as thoroughly as possible, and the accompanying what-if questions should cover all the ranges of possi- ble scenarios. Keep in mind that no checklist nor list of what-if questions can cover every possibility. The people involved in the DHA are responsible for adding items to these lists as they see fit. These lists must be flexible to cover all the foreseeable problems that are feasible, which can include some problems that aren't even reasonable. The use of a risk assessment matrix is of great help once a hazard is determined. cles as dust is more flammable and, thus, is the true hazard. • Document everything to make sure you can defend your testing results as you may have to defend your efforts and results in court. • K St and P max are necessary to know for mitigation and protection determination regarding explo- sion vents, isolation valves, and others. • MIE and MEC are critical in determining the actual hazards and risk levels in processing and bulk handling operations, such as convey- ing, milling, and dust collection. MIE and MEC can also indicate materials that are subject to increased risk of electrostatic discharge ignition. • Don't ignore other characteristics such as parti- cle size, moisture levels, adhesive and cohesive properties, temperature, and others. Any variable that'll influence the analysis should be considered. While the previous tasks are compulsory (to this author), the following are additional prerequisites that'll prove most helpful to the DHA. • Provide up-to-date schematic flow diagrams of the processes and systems where combustible dusts are present. • Provide layout drawings where feasible with building information. • Take pictures, videos, or both of the processes. Pictures help people remember and understand where obvious problems exist. Additional good-to-have information includes doc- uments associated with NFPA 652, Chapter 8, "Hazard Management: Mitigation and Prevention." Document examples include management of change, emergency plans, operating procedures and practices, personal FIGURE 1 Typical risk assessment matrix example with legend Risk probability Risk severity Catastrophic A Hazardous B Major C Minor D Negligible E Frequent 5 5A 5B 5C 5D 5E Occasional 4 4A 4B 4C 4D 4E Remote 3 3A 3B 3C 3D 3E Improbable 2 2A 2B 2C 2D 2E Extremely improbable 1 1A 1B 1C 1D 1E Color Risk level Red High Yellow Moderate Green Low