Materials that do not flow well form an arch or span across sloping sides of a blower truck body, leaving a void. This prevents material from continuing to move into the feeder, reducing material or halting discharge. Bridging typically occurs in force feed systems.
Bridging is a serious problem, and clearing material can cause serious injury or even death. The only safe way to free the material is to stop the blower truck, open the back door, and shovel the bridged material out of the truck. It is dangerous and never permissible to be inside the box of an operating blower truck.