Issue link: http://www.e-digitaleditions.com/i/796485
D ust collection systems are engi- neered and designed to minimize worker exposure to nuisance and haz- ardous dust generated by some types of production equipment. Dust capture hoods pick up airborne dust from bulk solids handling processes such as con- veying, mixing, blending, and packag- ing, and ductwork carries the dust to a dust collector for filtration, contain- ment, and safe disposal. A properly en- gineered dust collection system can significantly reduce inhalation and ac- cumulation of unsafe respirable or com- bustible dust in your plant. Shop drawings provide the con- tractor's fabrication and installation crews the details of what is to be built and installed. For a dust collection sys- tem, fully dimensioned shop drawings call out details such as ductwork size, type, and location; capture-hood con- struction details; sheet metal gauges; supports; and attachments to produc- tion equipment. The drawings should show plan and elevation views of all in- stalled components and should leave nothing to the imagination. Engineering/design documents, on the other hand, typically aren't de- tailed enough to be used for construc- tion and don't call out all the items listed in the specifications. They rarely show complete information, such as capture hood details; precise locations of system components on process equipment; and actual ductwork loca- tions with respect to existing plant in- frastructure. Also, the documents aren't always clearly written, which can lead to confusion about the engineer's meaning in some cases. Shop drawings bring all these potential problems to the forefront, so they can be corrected prior to fabrication and installation. Construction RFPs must require the contractor to submit the shop draw- ings to the project engineer for review and approval before construction be- gins. This review and approval process ensures that the fabricated and installed system will be satisfactory and mini- mizes the chance of installing the wrong type or size of equipment, such as the exhaust fan and dust collector. This is the time to catch and correct er- rors in materials, ductwork sizes, cap- ture-hood designs, and application of code requirements. The project engi- neer will then send the marked-up shop drawings back to the contractor for cor- rection and resubmittal. The project engineer's review is only to ensure that the shop drawings conform to the design concept and comply with the information shown in the engineering/design and specifica- tion documents. The contractor is still required to comply with all contract re- quirements. While requiring in the RFP that the contractor provide shop drawings for the project may sound obvious, it's not done often enough. Some contrac- tors may say that the engineering/de- sign and specification documents are good enough to be used instead of shop drawings. This is often because the con- tractor didn't include the cost of pre- paring the shop drawings when pricing the project proposal. Some contractors may say that you don't need shop drawings or that shop drawings will make the project take longer or cost more. On the contrary, shop drawings can save the contractor time and money by providing an or- derly set of fabrication documents. This can eliminate the constant stream of questions from sheet-metal workers at- tempting to build system components with insufficient information and en- sure that those components flow effi- ciently to the field for installation. Contractors should compare the money saved by not preparing shop drawings to the cost of replacing components that were improperly built or installed because of errors or misunderstandings caused by working only from engineer- ing/design documents. Another advantage to requiring shop drawings is that you'll have a com- plete and accurate set of documents showing the system "as built" for your records. PBEI John A. Constance The Engineers Collaborative Canandaigua, NY USA +1 215 300 9563 jac@engcollab.com www.engcollab.com PBEI | March 2017 7 Requiring shop drawings for new dust collection systems DUST D octor John A. Constance Send your dust collection questions to the editor, Jan Brenny (jbrenny@cscpub.com). A dust collection expert will answer them in a future issue.