Respecting your system's safety hazards
In this twelfth column on the general application of pneumatic conveying, we'll discuss some of the safety hazards associated with pneumatic conveying systems. Although these systems don't have a lot of moving parts and, in fact, appear to be fairly harmless, every year people are injured or killed as a result of working with them. Treating your system with respect and following safe practices when working near it can help you avoid many pneumatic conveying safety hazards. The following sections describe and explain how to avoid these hazards, including material bridges and buildup, system air pressure, system vacuum, safety switches and moving parts, and inert gas. [Editor's note: This column doesn't cover explosion prevention techniques. Find articles on explosion prevention and protection listed under "Safety" in Powder and Bulk Engineering's comprehensive "Index to articles," in the December 2001 issue or at www.powderbulk.com.]
Whether material has bridged or built up in a bin, tank, or large silo supplying your pneumatic conveying system, the blockage can be dangerous. Worker injuries often result when someone tries to remove a material bridge across the storage vessel's discharge opening or remove buildup on the vessel walls. Such buildup commonly results when the material is a fine powder or contains moisture or fat. A bridge across the discharge opening stops material flow and will eventually stop production. Rapping on the vessel wall where the bridge or buildup occurs frequently breaks up the material and restores flow, but not always. What can an operator do when continual rapping doesn't restore flow?