Browsing by Subject "Deflagration"
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Item Cotton Gin Dust Explosibility Determinations(2014-01-06) Vanderlick, Francis JeromeFollowing the recent Imperial sugar dust explosion in 2008, a comprehensive survey of past dust explosions was conducted by the Occupational Safety and Health Administration (OSHA) to determine potential explosible dusts. After the survey, OSHA personnel listed dust found in cotton gins, or gin dust, fueled two explosions in the past. OSHA is required by law to regulate facilities handling explosible dusts to provide a safe working environment for employees. The dust handling facilities must test the dust for explosibility based on the American Society for Testing and Materials (ASTM) E 1226 to ensure proper regulation of facilities. Dusts found in cotton gins were tested to determine if they are explosible. Safety Consulting Engineers Inc. (SCE) personnel tested gin dust in accordance with the ASTM method and reported that gin dust (GD) was an explosible dust. However, personnel from the Center for Agricultural Air Quality Engineering and Science (CAAQES) utilized the CAAQES test method and reported that gin dust was non-explosible. The goal of this research was to analyze the two different test methods and determine if gin dust should be regulated as an explosible dust. It is assumed that either the ASTM or CAAQES test method had incorrectly classified gin dust. The CAAQES test method was analyzed and tests were conducted on multiple dusts to the accuracy of the test procedure. A theoretical analysis of the ASTM test method was conducted to determine potential flaws in the test method. The ASTM test method was found to be flawed. It used pressure as the only criterion for a dust explosion, utilized high energy ignition sources, limited the amount of oxygen, and had no requirement for a dust to have a minimum explosible concentration (MEC) to be classified as explosible. Utilizing high energy ignition source can result in a determination that a dust explosion occurred when the measured reaction was actually due to the ignition source and not a dust explosion. This type of test is referred to as an overdriven test. The CAAQES test method utilizes three criteria: a ruptured diaphragm, flame front leaving the chamber, and a characteristic pressure versus time curve to determine if a dust has a MEC. If a dust has a MEC, it is an explosible dust. By determining the MEC a more accurate classification of a dust can be made by utilizing the CAAQES test method, as CAAQES personnel did to determine that gin dust is not an explosible dust. An analysis of the ASTM and CAAQES explosible dust testing protocols was conducted to determine proper classification of gin dust. Primary dust explosions occur in the process stream of facilities at locations where an explosible dust is entrained at concentrations above the MEC. A primary dust explosion may result in a series of secondary dust explosions. For a dust explosion to occur four criteria must be met simultaneously: there must be containment, a dust entrained in the air at or above the MEC, oxygen must be present, and there must be an ignition source. A theoretical analysis was conducted to determine if a MEC exists in a cotton gin. The results indicated that there were no locations in a cotton gin where aMEC existed. It was concluded that gin dust is not an explosible dust and that dust explosions are not possible in cotton gins.Item Hydrodynamical analysis of nanometric aluminum/teflon deflagrations(2008-05) Stacy, Shawn Christopher; Pantoya, Michelle; Levitas, Valery; Weeks, Brandon L.The hydrodynamics of deflagrations from reactive materials (RM) submerged underwater can be studied using a modified aquarium test. Normally loose powder RM will disperse after being submerged in water. Introducing hydrophobic materials such as Teflon into the reactant matrix, enables a barrier against permeation of water into the reactants. Also, ignition via resistance heating can be difficult underwater because significant energy is lost by convection off the wire into the water. Nano-Al particles require significantly less energy for ignition than their micron scale counterparts such that underwater ignition via resistance heating can be achieved. The objective of this study is to examine the reaction hydrodynamics from a submerged nano Al-Teflon mixture as a function of mixture composition and bulk density. Submerged Aluminum/Teflon mixtures were ignited and the ensuing reaction was recorded with a high speed camera and a pressure transducer. The resulting bubble shape, size, and pressure histories along with the burn time and rate allow the analysis and comparison of different fuel/oxidizer compositions and powder packing densities. Results show that as the density of the powder decreases the reaction transitions from a slow jet of multiple bubbles to quick single bubble. One observation is that as the percentage of aluminum increases the bubble radius also increases even though there is less of the gas producing Teflon in the mixture. This could imply that the excess aluminum is reacting with water.Item Initiation and detonation in lead azide and silver azide at sub-millimeter geometries(2006-12) Jung, Peter C.; Oler, James W.; Tappan, Alex; Weeks, Brandon L.The process by which an energetic material is initiated and transitions from burning to detonation has been investigated and documented in the literature for many different materials. The fast reaction velocities and short reaction lengths of primary explosives have limited the amount of research on the nature of their transient, developing, pre-steady-state detonation processes. The increased interest in micro electro-mechanical systems (MEMS) and the growth of small-scale manufacturing processes has led to the need for a better understanding of the properties of energetic materials at reduced length scales. This research made use of high-speed streak camera photography to study both the initiation properties and reaction velocities of lead azide and silver azide. The charges studied were cylindrical in shape and had diameters ranging from 200 µm down to 10 ìm. The samples developed for study in these experiments were cylindrical charges of either lead azide, Pb(N3)2, or silver azide, (AgN3), contained in micro-capillaries. A method for the reliable production of charges of both lead azide and silver azide in sub-millimeter geometries has been demonstrated. Results discussed include reaction velocity, observation of an accelerative reaction, observation of retonation waves, and the reaction of a lead azide charge as small as 10 µm in diameter.