It is unclear what NFPA 652 , "All components of enclosed systems that handle combustible particulate solids shall be designed to prevent the escape of dust, except for openings intended for intake and discharge of air and material." What is unclear is what it means by "prevent the escape of dust." Must all enclosed conveyors be "dusttight"?
652 184.108.40.206.2 states, “Coverings on cleanout, inspection, and other openings shall be fastened to prevent the escape of combustible dusts," which is very similar language to 220.127.116.11. However, the standard in 664, which references the same components, says, "Access hatches and removable equipment covers shall be tight fitting and securely fastened for dusttight operation" ( 18.104.22.168.7). "Dusttight" here is explained in the appendix, which says, "Gaskets or smooth machined mating surfaces are generally required for dusttight operation” (A.22.214.171.124.7).
Our concern is that there is an IP rating for "dusttight" operation. NFPA doesn't reference this rating, so its definition of "dusttight" may be less stringent. And NFPA 664 126.96.36.199.2 states, "All equipment shall be designed to minimize fugitive dust emissions from the equipment." This doesn't sound like a "dusttight" standard.
Thus, we are unsure what the codes mean, precisely. Must the entire conveyor be "dusttight" or must the conveyor, as a whole, generally control (i.e. minimize) dust? Must only the hatches and removable equipment covers be "dusttight?"
For some background, we manufacture conveyors and other material handling equipment. Our client base is largely in the wood manufacturing industry, and we are analyzing our designs and preparing for the questions we're bound to receive come mid-September when companies are required to complete their dust hazard analysis.