Researches on the failure process of coal during coal and gas outbursts are of great importance in underground mining. Based on the theories of coal spherical shell failure, coal spallation and coal powder pneumatic conveying, the flow state and transport mechanism of coal and gas outbursts were studied. This paper concludes that in the outbursts' development stage, with the front of the outburst being gradually exposed to air, the gas gradient behind the outburst acts as a reciprocating air knife of high pressure that cuts the ejected coal powders, thus forming a plug flow with a high solid-gas ratio and a low speed. By referring to the laboratory results from other researchers and data recorded from field outbursts, an appropriate explanation was obtained for the wave-like coal powder distribution and the sound explosion using the dense-phase plug flow pneumatic conveying theory, which conversely confirms the possible existence of the plug flow. (C) 2016 Elsevier B.V. All rights reserved.