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16 / May 2021 powderbulk.com DUST DOCTOR PBE John A. Constance, The Engineers Collaborative Dust collection system Q&A dust above those levels, your dust collection system's capture hood or hoods will need to be effective enough to reduce the dust concen- tration to acceptable levels. So, how do you determine the amount of airborne dust the dust capture hood(s) will need to capture? First, measure the dust concentration that's generated at the operator's breathing zone and in the operation area. Your industrial hygienist or an outside one can take these measurements for you. Then, with the air measure- ment results, you can specify the nuisance dust's airborne concentra- tion that the system's dust capture hoods need to achieve. A properly designed dust capture hood can reduce the dust's airborne concen- tration by an average of 90 percent without taking the process' solids away or interfering with the pro- duction operation. For instance, if your air measurements show the plant area's total dust concentration at 50 mg/m 3 , a properly designed dust capture hood can bring this level down to somewhere close to 5 mg/m 3 . If that level is satisfactory to you (and meets regulation stan- dards), you can specify to the dust collection system manufacturer that each dust capture hood achieve a total airborne dust concentration of less than 15 mg/m 3 without material loss and production interference. Also, as previously mentioned, you'll need to specify M any manufacturing pro- cesses in the powder and bulk solids industry work with material that creates dust, which needs to be removed from the work area. But dust collection systems aren't one size fits all, so the system needs to be tailored to your specific plant and application needs. Before you have a dust collection system designed and built for your plant, there are some questions you should ask. If you don't have the correct answers suitable for your application before the system is designed, fabricated, and installed, the resulting problems can be expensive to correct afterwards. What do you want your dust collection system to do? The first question you'll want to consider is what you want your dust collection system to do. If you don't specify the results you want the new or upgraded dust collection system to accomplish, you likely won't get the outcome you want. For example, let's say that a blender charging operation is generating fugitive dust. If the dust is considered a nuisance dust according to OSHA standards, the dust's allowable airborne concen- tration is 15 mg/m 3 of total dust in the plant area and 5 mg/m 3 of respirable fraction (amount that can be safely inhaled) within the plant personnel's breathing zone. 1 If your operation is generating nuisance that the dust collection system at each dust capture hood achieve a respirable dust concentration in plant personnel breathing zones of less than 5 mg/m 3 without material loss and production interference. An actual case at a manufac- turing company involved a toxic dust where the respirable exposure without dust collection was mea- sured at 0.82 µg/m 3 . The properly designed dust capture hood's installation reduced the exposure level to 0.054 µg/m 3 — a 93 percent decrease that satisfied the desired reduction target. If you don't achieve your tar- geted dust concentration reduction at dust collection system startup (your industrial hygienist performs air sampling with the dust capture hoods in place), the design engineer and contractor must correct the problem. In addition, if you don't specify your required dust collec- tion system performance results in your purchase orders to the design engineer and involved contractors, you won't get what you want, and correcting the problem will cost you more. Why do you need shop drawings? Having accurate dust collection system drawings is important to ensure you get the system you requested. Shop drawings pre- pared by the fabricating and installation contractor show the