(Including Work Restraint and Fall Arrest)
Work Restraint systems prevent a technician from reaching a place of danger and so are very safe techniques when used properly. Lanyards from a fixed anchor or rail systems on roofs are good examples of how to allow a technician space to move with minimal exposure to danger.
Despite being at the bottom of the Working at Height safety hierarchy, fall arrest systems are probably the most widely used of all in working environments as they are often cheap, quick and low profile. By accepting that falls may occur, then safety wise, it all depends on how the systems are used and the surrounding environments. Usually, they require a safe .dropzone. under the place of work so that the system is able to catch the technician without them striking any other hazards.
The techniques used by technicians include shock absorbing lanyards and inertia reels and systems may be permanently in place or set up temporarily depending on the duration of the tasks.