Location: Cotton Ginning ResearchTitle: A critical evaluation of combustible/explosible dust testing methods-part 1 Author
|Parnell, Jr, Calvin|
Submitted to: Journal of Loss Prevention in the Process Industries
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/4/2012
Publication Date: 7/25/2012
Citation: Parnell, Jr, C.B., McGee, R.O., Ganesan, B., Vanderlick, F.J., Hughs, S.E., Green, K. 2012. A critical evaluation of combustible/explosible dust testing methods - Part 1. Journal of Loss Prevention in the Process Industries. 26(3):427-433. Interpretive Summary: A question was raised by Federal regulators as to whether particulate found within the interiors of cotton gins would serve as fuel for dust explosions similar to what can occur in grain elevators. There is no anecdotal evidence in the cotton ginning industry of dust related explosions ever occurring in operating cotton gins. However dust collected from gin interiors had seemingly not been scientifically tested for any explosive properties. Samples of representative dust were collected from several cooperating cotton gins and tested by two different entities. The dust samples were split and tested by the Center for Agricultural Air Quality Engineering and Science, Texas A&M University (CAAQES) and by Safety Consulting Engineers Inc. (SCE). The two entities used very different test methods to test the explosibility of the dust samples. The SCE used protocols specified by ASTM E1226 and E1515 that suspend known quantities of dust in an enclosed chamber with a 10 kJ ignition source to check pressure rise within the chamber. A pressure rise above a specified limit after powering the ignition source is supposedly an indicator of explosibility of the dust being tested. The SCE determined that the gin dust was explosible by their method. The CAAQES used a different method that first determined if there was a minimum explosive concentration (MEC) of suspended dust within an enclosed chamber. If the MEC existed using the CAAQES test system then the dust was defined as explosible. The CAAQES tests determined that 1) gin dusts were not explosible, and 2) the tests conducted by SCE were “over-driven” by the large ignition source and gave a false positive reading. The two testing entities were not in agreement on their results but the CAAQES conclusion corresponds with current anecdotal evidence that dust suspended in the interior of commercial ginning operations is not explosible. This report is the first part of a larger discussion of proper test methods for determining the explosibility of any particular dust.
Technical Abstract: Tests were conducted by the Center for Agricultural Air Quality Engineering and Science (CAAQES) and by Safety Consulting Engineers Inc. (SCE) to determine if dust found in cotton gins (gin dust) would serve as fuel for dust explosions. In other words, is gin dust explosible? The laboratory tests used by CAAQES and SCE are very different. SCE used a totally enclosed 20 liter (L) chamber, flame from a 10,000 joule (10 kJ) ignition source, reported that gin dust was a class ‘A’ explosible dust. CAAQES used a 28.3-L (1 ft3) chamber with diaphragm, a stationary coil as the igniter, video and pressure recordings of each test and concluded that gin dust was not explosible. SCE followed the protocols specified by ASTM E1226 and E1515. The only indicator used to determine whether a deflagration occurred during a test was pressure. If the pressure rise exceeded one bar gage (g) in a 20-L chamber test with a flame from a 10 kJ energy source as the igniter, it was assumed that a deflagration occurred in the chamber and the dust was classified as explosible. The CAAQES criterion for determining if a dust was explosible consisted of determining the minimum explosive concentration (MEC). If the MEC existed using the CAAQES test system, it was explosible! The criteria used with the CAAQES method for determining the MEC was to test concentrations starting at concentrations above the MEC and lowering the concentrations until at least one of the three tests at that concentration failed to result in a deflagration. The indicators of a deflagration were (1) bursting of a diaphragm, (2) flame front leaving the chamber and (3) characteristic pressure vs. time curve. It was concluded that the ASTM method of using only pressure as the indicator of a deflagration in a totally enclosed chamber would likely result of an “over-driven” test and an incorrect finding that gin dust was explosible. The result of CAAQES testing was that gin dust was not explosible.