Sapphire and Steel’s unheimlich opening narration

“All irregularities will be handled by the forces controlling each dimension. Transuranic, heavy elements may not be used where there is life. Medium atomic weights are available: Gold, Lead, Copper, Jet, Diamond, Radium, Sapphire, Silver and Steel. Sapphire and Steel have been assigned.”
-Opening non-explanation for Sapphire and Steel

Sapphire and Steel was the real vehicle for terror in my childhood. Never mind hiding behind the sofa. This was a programme to be watched through a crack in the door from the next room.