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
Shale gas in the United States infrastructure emerged as environmental concerns for the rush. In Pennsylvania, controversy has surrounded the practice of releasing wastewater from "fracking" into rivers which serve as consumption reserves. Methane release contributing to global warming is a concern. The word “fracking”, slang for hydraulic fracturing, has entered the English language. The Great Shale Gas Rush refers to the growth in unconventional shale gas extraction in the early 21st-century. Pennsylvania was featured in the Academy Award-nominated, environmental documentary Gasland by Josh Fox in 2010. Most of the filming for the 2012 Gus Van Sant dramatic film, Promised Land, starring Matt Damon, took place