Hydrogen sulfide is associated with most of the fatalities from manure storages, both human and animal. Carbon dioxide is a non-toxic gas, but it does replace oxygen and, therefore, can asphyxiate humans and animals. Because it is colorless and odorless, carbon dioxide is impossible to detect without gas detection equipment. Since it is heavier than air, it usually accumulates near the bottom of the storage. Carbon dioxide does not usually build up to the point that is becomes lethal unless all ventilation into and around the pit has been eliminated for a few hours.
Ammonia can cause severe damage to the eyes, throat, and lungs.
This gas combines with moisture in the eyes and respiratory tract to form an alkaline base, which results in severe burns. Ammonia is lighter than air and has a strong bleach-like smell. Because of its irritating nature, people usually leave the area quickly. Therefore, it is not suspected to have caused any human deaths. However, constant low-level exposure to ammonia can have a discomforting effect on humans and livestock.