An Improved Method to Determine the Explosibility of Dust Over the ASTM Explosible Dust Testing Standards

The explosibility of a dust is tested using a 20L semi spherical chamber specified by ASTM E1515 and E1226 standards. The dust cloud is ignited with 5KJ or 10 KJ pyro-technic igniters and the rise in pressure is recorded. Pressure rise is the only criterion used to determine the explosibility of a dust. The requirements for a dust explosion to occur are (i) Fuel at or above the minimum explosible concentration (MEC) (ii) Oxygen (iii) Ignition source and (iv) Containment.The Cotton Ginning Research Laboratory had collected cotton gin dust (CGD) samples across the cotton belt and forwarded it to Safety Consulting Engineers Inc. (SCE) and Center for Agricultural Air Quality Engineering and Science (CAAQES). SCE conducted tests based on the current ASTM standards and reported CGD was a Class A explosible dust. Using a unique realistic test system, CAAQES reported CGD was not an explosible dust. In the ASTM method, the dispersed dust cloud was ignited by a flame from a 10 KJ pyrotechnic ignitor that burns the dust rather than resulting in a self-propagating flame and the resulting pressure is the only indicator of a deflagration. In the CAAQES method, the dust sample is dispersed by compressed air and the dust cloud is ignited by a stationary source. If an MEC exists, the resulting flame and the pressure wave rupture the diaphragm and leave the chamber. A characteristic pressure vs. time curve is recorded for each test. This testing methodology with a stationary ignition source and a diaphragm ensures the self-propagation of the flame. The CAAQES method classifies a dust as explosible only if it has a MEC, which is verified by not only the pressure vs. time curve but the visual and audible indications of a deflagration by the bursting diaphragm.