Lethality of electricity is multi-dimensional, trying to reduce it to a single quantity does not really work (exposure time and electrical frequency are very important).
Sounds a bit like fuse wire (except the frequency dependence)... There's both a current and a time component. High overloads can be tolerated for a very short time without blowing the fuse, while low overloads can be sustained for longer before the fuse reaches its maximum temperature and breaks.