A primary cause in many industrial accidents is that equipment that is “under repair” starts or moves suddenly while the worker is in a dangerous position within the machine. This can happen when there is a failure to properly identify, isolate, and eliminate stored energy sources within equipment prior to beginning maintenance tasks. This stored energy (often referred to as“potential energy”) can be very dangerous if not dissipated as it can cause unexpected machine movements, even when the machine is “turned off”. Residual pressure in hydraulic or pneumatic lines, stored electrical energy, and stored pressure in compressor tanks or accumulators are examples of the potentially hazardous energy.