Milling Journal - Q1 2008 - (Page 48)

from the effects of an explosion. If the latter, can the pressure and flame from an explosion be contained or controlled within a single vessel, or does the propagation between vessels need to be considered? 3. Make a final decision on your approach. Several options are available. • You can try to contain the explosion within a single vessel, but this can be costprohibitive. • You can control explosion-generated flame and pressure through suppression. • You can control explosion-generated pressures through venting. • You can control the propagation of pressure and flames through isolation. Explosion Suppression These types of devices reduce the maximum pressure from an explosion below the design strength of the vessel— minimizing damage from the pressure and flames of the explosion. They include a pressure detector that signals a control device to react in the event of an explosion and release a flame-suppressing chemical, such as sodium bicarbonate. This approach may involve several detectors and multiple suppressant discharge containers, depending on the size of the vessel. They may be installed on all types of equipment around the mill, including dust collectors, dryers, roller mills, and bucket elevators. Explosion Isolation Relatively small explosions can become major, deadly explosions as pressure and flame travel from vessel to vessel through pipes and ducts, lofting and igniting dust as they move along. Explosion isolation systems prevent this through the use of pressure or optical sensors, which activate devices in the pipes or ducts to block the spread of the explosion, isolating it from the rest of the plant. These devices might include a slide gate across “Relatively small explosions can become major, deadly explosions as force and heat travel from vessel to vessel through pipes and ducts, igniting dust as they move along.” the pipe or a valve that releases a fire suppressant such as sodium bicarbonate. A challenge with this type of system is making sure that the barrier is in place before the flame front reaches it. Explosion Venting Venting controls explosion-generated pressure by releasing it from the vessel through an opening of pre-determined size and location. The vent closure responds to the explosion pressure by moving out of the way of the blast wave and flame front. The required size and location is determined using NFPA 68 equations. Vent placement must be considered carefully to determine what external damage could occur when the vent closure is blown out and flame and pressure are released. NFPA 68 prohibits indoor venting but permits ducting to the outdoors or the use of a flameless venting device. Ed Zdrojewski, contributing editor 48 First Quarter 2008 Response No. 481 MILLING JOURNAL http://www.beltzmilling.com http://www.beltzmilling.com

Table of Contents Feed for the Digital Edition of Milling Journal - Q1 2008

Milling Journal - First Quarter 2008 Contents First Break Examining Fortification Standards IAOM 2008 Milling Short Courses 2008 IAOM Conference and Expo Melinda Farris Interview Designing a Purifierless Millflow Dirk Maier Named KSU Dept. Head NAMA’s 2008 Division Meetings Protecting Electrical Workers Miller Profiles Todd Bastean Interview Safety: How Serious Are We? Product Quality/Gwirtz Product Roundup: Magnets Pest Management/Subramanyam Explosion Protection Supplier Interview: Darin Stutler Product Reviews New IAOM Safety Award Criteria Don’t Forget OSHA Form 300A Milling Notes Great Lakes Regional Conference 4th Quarter 2007 Flour Production IAOM Reference Guide Hammermills Brushes Aspirators Level Indicators Product Reviews Magnets Mixers Packaging Purifiers Safety Equipment Screeners Separators Sifter Accessories Ad Index

Milling Journal - Q1 2008

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