Explosion characteristics of three component hybrid mixtures

Hybrid mixtures of a combustible dust and flammable gas are usually found in many industrial processes that handle combustible dust, vapor or gas. The work of this paper investigates the explosion behavior of mixtures consisting of three flammable components and air. The materials used in this case are corn starch, methane and acetone in vapor state. The experiments took place in the standardized 20 L explosion sphere where modifications were done to allow input of solvent and gas. The test protocol was according to EN 14034 with electrical igniters as ignition source but in the case of pure dust tests both chemical and electrical igniters were used. The experimental results demonstrate the significant enhancements in explosion likelihood and explosion severity when small amounts of solvents or gases below their respective lower explosion limits were mixed with dust. They also confirm that a hybrid mixture explosion is possible even when dust, gas and vapor concentrations are respectively lower than their minimum explosion concentration (MEC) of dust and lower explosion limit (LEL) of gas and vapor. Considering dust as main component the results presented show that the addition of less than 4 vol. % of gaseous fuel significantly lowers the MEC of starch from 250 g/m3 to 5 g/m3 and also increase the explosion severity of the dust. In the case of gas/vapor, the addition of starch below the MEC decreases the LELs from 4.9 to 1.0 vol. % and 2.5 to 0.5 vol. % for both methane and acetone respectively.