Inert gas asphyxiation lacks oxygen and consists of an asphyxiant gas (one or more of argon, nitrogen or carbon dioxide), causing the animals to lose consciousness. Argon and nitrogen are important components of a gassing process which seem to cause no pain, and for this reason many consider some types of controlled atmosphere killing more humane than other methods of killing. However, "stunning" is often done using carbon dioxide. If carbon dioxide is used, controlled atmosphere killing is not the same as inert gas asphyxia, because carbon dioxide at high concentrations (above 5%) is not biologically inert, but rather is toxic and also
Natural gas in the United States sealed with rope and molten lead. In the 1800s and early 1900s, most natural gas discoveries were made while exploring for oil. Natural gas was usually an unwanted byproduct of oil production. In the 1870s steel pipe replaced cast iron. In 1883, Pittsburgh became the first major city supplied with natural gas. Other cities followed, but only if they were close to natural gas wells. Because natural gas was a byproduct, it was priced cheaply, and, where available, undercut the market for town gas. In 1891, one of the longest pipelines of the time was built, a 120-mile long pipeline