Methane is colorless, odorless and lighter than air. It is given off in considerable quantity from anaerobic action. However, it is formed by a highly specialized group of bacteria, and conditions normally found in confinement facilities are not conducive to producing significant amounts of methane. The more important danger of methane is perhaps its explosive characteristic at concentrations of 5 to 15 percent. While this gas is normally considered nontoxic, it has an asphyxiating effect.
Carbon dioxide is colorless, odorless and heavier than air.
It normally makes up 30 to 60 percent of the gas resulting from anaerobic stabilization of manure. Carbon dioxide is not highly toxic. However, its greater danger is asphyxiation due to depletion of oxygen supply in the air. Concentrations of carbon dioxide greater than 4 percent are cause for concern for both humans and livestock. However, it is easily recognized by its pungent odor.