A boom truck is a type of mobile crane that uses a boom to lift heavy loads onto its bed, but its lifting capacity can be exceeded if the load's center of gravity moves too far from the crane's tipping axis during lifting movements like extending the boom or rotating the upper deck. This can cause the crane to become unstable and collapse. To prevent boom collapse, operators must be trained, fall protection must be worn, safety devices cannot be overridden, inspections must be performed, only authorized people can operate the crane, load weights must not exceed capacity, and outriggers must be used if provided.