as anesthesia by dentists, better known as laughing gas; hydro fluorocarbons, which are used in refrigerators and aerosols; per fluorocarbons, a gas permeated by fire extinguishers, refrigerators and high end ski waxes; and sulfur hexafluoride, more commonly known for its use in circuit breakers, switchgear and other electrical equipment.This leaves Americans between the proverbial ???rock and a