Spark arresting module

In a duct for conducting stack gases, a spark barrier comprising a rigid frame, transversely-spaced bars having broad and narrow sides positioned in the frame with the broad sides spaced apart in parallel relation and defining narrow spaces between the broad sides corresponding in width to the width of the narrow side and with the narrow sides at both front and back of the frame lying in planes perpendicular to the front and back sides, said frame when supported in a duct as a barrier presenting the narrow sides of the bars at right angles to the direction of flow of the gases through the duct and the broad sides parallel to the direction of flow of the gases through the duct, a shaft, means supporting the shaft in a position parallel to the plane containing the narrow sides of the bars at the front upstream side of the frame and at right angles to the longitudinal dimensions of the bars and spaced therefrom at the upstream side, a plurality of blades corresponding in number to the number of the spaces between bars fixed to the shaft with adjacent blades angularly displaced at right angles to each other, each blade comprising base-to-base trapezoidal vanes extending radially from the axis of the shaft, one-half of the base of said vanes being greater than the distance between the axis of the shaft and the plane in which lie the narrow sides of the bars at the front side so that portions of the blades are always located between the bars at the front side and means for effecting rotation of the shaft.