According to the CySA SYBEX book, in chapter 1, power failures are listed as both environmental threats and structural threats… but which one is it?
According to the book:
Environment threats occur when natural or man-made disasters occur that are outside the control of the organization. These might include fires, flooding, severe storms, power failures, or widespread telecommunications disruptions.
At the same time,
Structural threats occur when equipment, software, or environmental controls fail due to … environmental controls (such as power and cooling infrastructure) …