High-voltage transmission lines carry electricity from switchyards to local power grids, substations and other facilities. Transmission lines are designed to carry high voltages in order to minimize the energy loss that naturally occurs over long distances. Most of these lines span between tall transmission towers, while a small number are underground.
Overhead transmission lines are not insulated, and contacting them is dangerous. The coating on power lines is designed for protection from the weather and will not prevent electric shock. Even approaching the lines with aerial equipment or extinguishing agents can cause electric arcing. This is why transmission line emergencies require large safety clearances, as well as unique response tactics.
Even deenergized transmission lines can hold a charge that can be fatal or extremely hazardous. Keep yourself and all equipment at least 100 feet away from these lines unless the the local utility company has verified they are properly grounded and safe to contact.