"Dead-man" safety switch for HV bench work?
Not exactly. The way this is handled in every high voltage laboratory I have worked in is that the machine area is cleared of people and safety gates deployed before charging can commence, and opening any of the safety gates will abort the machine (sometimes messily - but damaging the machine is considered preferable to killing people; in practice, I don't think anyone ever was clueless enough to open a gate with a shot in progress while I worked at the various places.)