This four-part series presents guidelines for: electrically isolated inputs and outputs; measuring the performance of hospital biomedical engineering programs; evaluating the risk of electric shock in hospitals; and for isolated power in anesthetizing locations. Parts I and II, covering the first two topics above, were published in the Oct.-Dec. 1980 issue of this Journal.Part III constitutes an attempt to place the risk of electric shock in hospitals in a quantitative perspective. Arguments are presented that indicate that electrical safety precautions usually take up a larger share of the hospital's biomedical equipment safety budget than is justified by the actual hazard levels.Part IV reviews the need for isolated power in anesthetizing locations. Three independently proposed revisions to the 1973 edition of NFPA Standard 56A would have significantly simplified the safety requirements for hospital anesthetizing locations (a) by reducing the area in flammable locations classified as hazardous to the internationally accepted “zone of risk,” and (b) by permitting the use of conventional electrical power rather than isolated power in locations where the risk of electrical accidents can be shown to be no greater than it is in other areas of the hospital. Despite extensive technical testimony supported with substantial supporting documentation, the revisions were vetoed by the Technical Committee after they were voted into the document by a floor vote of the general membership attending the NFPA Annual Meeting in Anaheim in 1978. The chronology of the major events surrounding the subsequent appeal of this veto is traced back to 1974, and an analysis is presented of what are considered to be shortcomings in the NFPA appeals process revealed by this particular case history.