Location: Cotton Ginning ResearchTitle: Combustible dust tests) Author
|Hughs, Sidney - Hughs Ed|
Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: 2/10/2011
Publication Date: 4/26/2011
Citation: Parnell, C.B., Mcgee, R.O., Vanderlick, F.J., Contreras, A., Hughs, S.E., Green, K. 2011. Combustible dust tests. National Cotton Council Beltwide Cotton Conference. 479-489. Interpretive Summary: An explosion caused by suspended dust in a sugar mill in 2008 killed 14 workers and injured others. This incident caused OSHA to revise its program of inspecting facilities who handle materials that generate suspended dust which are combustible and may create an explosion hazard. Besides sugar, other agricultural operations such as grain elevators also handle dusts that can reach concentrations suspended in air which can rapidly ignite causing an explosion. The question arose whether dust found in cotton gins could reach suspended concentrations that might cause an explosion similar to sugar or grain dust. Cotton gins do not have a history of dust explosions but it was deemed necessary by industry representatives to formally test interior cotton gin dust for its ignition potential. Dust that had settled on the interiors of cotton gins across the cotton belt was collected after the 2009/2010 ginning season for testing its potential to cause a dust explosion. Testing was done at the Center for Agricultural Air Quality Engineering and Science (CAAQES), College Station, TX using a method developed by CAAQES and a commercial testing laboratory that used two standard testing protocols. Tests conducted at CAAQES determined that gin dust was not combustible. Tests from the commercial laboratory were mixed with one test method determining that gin dust was not combustible but a second; following test determining that gin dust met the criteria for being classified as combustible. This paper discusses the separate tests and their conflicting results.
Technical Abstract: The sugar dust explosion in Georgia on February 7, 2008 killed 14 workers and injured many others (OSHA, 2009). As a consequence of this explosion, OSHA revised its Combustible Dust National Emphasis (NEP) program. The NEP targets 64 industries with more than 1,000 inspections and has found more than 4,000 combustible dust related violations. Many agricultural operations handle products such as grain and sugar that results in concentrations of combustible dust that can fuel deflagrations (explosions). It has been alleged that dust found in cotton gins is a combustible dust. Tests were conducted by the Center for Agricultural Air Quality Engineering and Science (CAAQES) and by a commercial laboratory to determine if gin dust was combustible. CAAQES reported that gin dust was not a combustible dust. The commercial laboratory reported that gin dust was a class "A" combustible dust. The justification of classifying gin dust as combustible dust was based upon a requirement that the dust be tested in 20 L spherical chamber with a 10,000 J chemical igniter sprayed through the dust cloud. Using a bench mark of 2 bars pressure rise as an indicator that an explosion occurred in the test chamber, it was determined that gin dust was combustible. The authors of this paper point out that burning of dust will result in a rise of pressure sufficient to exceed that benchmark of 2 bars resulting in an incorrect classification for gin dust. The CAAQES method uses tests for determining the minimum explosive concentration (MEC) as the criterion for determining whether a dust is a combustible dust or not. Numerous tests were conducted on corn starch, dust XX, and gin dust to determine MECs. The MECs of corn starch and dust XX were 43 g/m3 and 73 g/m3. There were no deflagrations for any concentration of gin dust tested. It was concluded that gin dust did not have an MEC and therefore was not a combustible dust.