Paul, from what I have gathered, the immersion detectors respond to conductive liquids modifying the impedance between a sensor probe and an electrode. It will trip the H & N open when the appliance is dropped in water. Its supposed to limit leakage to 6 mA..just like a gfci, but its not to be relied upon to prevent a momentary tingle. But it still sounds safer than the 30mA device that you mentioned.
As for the controversy about stray EMF from power systems, our IEEE published findings that pretty much aleviate fears of the power line and building wiring EMF having any deleterious effect on humans..as you probably are aware (you appear to be a really smart guy!). The energy of power wiring is negligible compared to the normal thermal energy in the human body. But, electromagnetic interference can still be a problem and so I would not be too keen about an open in a ring circuit. You can check Mike Holt's web site for further elaboration.
Sparky, if you are reading this I have a question for you: where can I download a copy of the latest ROP's and ROC's?
