Demolition work can be hazardous due to unknown factors such as deviations from the structure's original design, materials hidden within structural members, and unknown strengths or weaknesses of construction materials. To counter these unknowns, all personnel involved in a demolition project must be fully aware of the safety precautions to take to control these hazards. Preparatory operations for demolition involve the overall planning of the demolition job, including the methods to be used to bring the structure down, the equipment necessary to do the job, and the measures to be taken to perform the work safely.