We study methane backward flow in the laneways at various wind velocities and angles based on computational fluid dynamics theory;analyze the backward flow area length,the concentration distribution and the methane roof layer thickness.The results show that the methane roof layer would move against the airflow in a declensional ventilated airway if the downward air velocity is not large enough.The faster the airflow speed,the smaller the methane backward flow area becomes,and the methane roof layer becomes ...