(75c) A Correlation for the Lower Flammability Limit of Hybrid Mixtures

Hybrid mixtures explosions involving dust and gas can cause great loss of lives and properties. A recent coal mine explosion in Upper Big Branch Mine, West Virginia in April 2010, resulted in the loss of 29 miners’ lives. Hybrid mixtures are also widely encountered in industries such as paint factories, pharmaceutical industries, or grain elevators. The lower flammability limit (LFL) is a critical parameter when conducting a hazard assessment or developing mitigation methods for processes involving hybrid mixtures. Unlike unitary dust or gas explosions, which have been widely studied in past decades, only minimal research focuses on hybrid mixtures, and data concerning hybrid mixtures can rarely be found. Although methods to predict the LFL have been developed by using either Le Chatelier’s principle which was initially proposed for homogeneous gas mixtures, or the Bartknecht formula which was adopted for only certain hybrid mixtures, significant deviations still remain. A more accurate correlation to predict an LFL for a hybrid mixtures explosion is necessary for risk assessment.

This work focuses on the study of hybrid mixtures explosions in a 36L dust explosion apparatus using a mixture of methane/cornstarch in air. By utilizing basic characteristics of unitary dust or gas explosions, a new formula is proposed to improve the prediction of the LFL of the mixture. The new formula is consistent with Le Chatelier’s principle or the Bartknecht formula.