Ah, risk--an issue close to my heart, and an interesting conversation. I'd like to put in my 2 cents. "low" risk piece of equipment may actually pose a "high" risk." Agree totally, which is why I like, "The chance of the device's faulty state being noticed by a non-technical person" as a risk characteristic, while "A device's likelihood of breaking down" I've found unreliable as an indicator--assuming the device is not new. We've used 4 weighted criteria plus 1 additional: does the device have 100% electronic self test?, will failure be apparent to user?, does device require cal, lube, or part?, is consequence of failure great?, and 5, have defects been found during inspections that users missed (how effective maintenance is)? There ARE some elaborate formulas, but often they rely on more arbitrary input than they're worth.
