Re: Impact Assessment
I had to produce written risk assessments for pretty much anything we did that had any possible significant risk. Things like taking kids with serious behaviour difficulties on a school trip, crossing major roads, I did RA refresher courses every few years.
The principle is simple enough, even of the methods vary. You gauge probability - not usually a number, because that's impossible. There are too many variables in too many combinations.
And you multiply by the severity of outcomes.
In this case maybe likelihood of loss of power I'd maybe put as Low based on that 1:100 figure, ( not my own guess, which would have been at least a cynical Medium).
But consequence as Very High. (Loss of valuable equipment, data, business and lives)
On the basis that LowxHigh=Medium I'd have said this was a Medium to High risk.
And that's how I always produced my RAs. Which also had to contain a plan to minimise risk.