It is a common belief among farmers that it is safe to enter a facility or pit if they cannot smell the putrid, rotten egg odor associated with hydrogen sulfide. This is not necessarily true because high concentrations of hydrogen sulfide paralyzes the nerve cells of the nose to the point where the person can no longer smell the gas. Hydrogen sulfide, because it is heavier than air, accumulates above the liquid level of the pit. Individuals may be quickly overcome with hydrogen sulfide when working around a pit, whether it be climbing down a ladder to make repairs or when leaning down to take a manure sample. This gas is released throughout the year from urine and feces on the facility floor, or from a pit beneath the floor.
Ammonia is lighter than air and generally dissipates from a well-ventilated facility.
Concentrations ranging from 6 to 20 ppm and above will irritate the eyes and throat. At higher concentrations, ammonia can irritate the respiratory system and cause wheezing and shortness of breath. Concentrations above 2500 ppm are considered to be dangerous to human life, but individuals are not likely to enter a facility with a concentration this high because of the extremely strong odor. A colorless, odorless, non-toxic gas that is lighter than air, methane generally dissipates from a confinement building. The risk of fire is greater in a poorly-ventilated structure.