Ammonia is released from decomposing manure and urine. It can slow growth rate and reduce feed conversion efficiency. If also hinders the lungs’ normal ability to remove or destroy airborne disease organisms that are inhaled, increasing the chances of respiratory infection. The recommended maximum exposure limit to ammonia is 20 ppm for pigs, poultry and calves, and 7 to 10 ppm for humans.

Hydrogen sulfide, also known as pit gas and recognized by its characteristic rotten egg smell, can be deadly to pigs and humans exposed to a concentration as low as 20 ppm. While day-to-day concentrations of hydrogen sulfide are generally safe, dangerous concentrations can sometimes be measured during agitation of manure during pit pump-out procedures. The recommended maximum exposure limit to hydrogen sulfide is 10 ppm for pigs, poultry and calves, and 5 ppm for humans.

Carbon monoxide is a colorless, odorless gas given off by gas-fired supplemental heaters that are not burning fuel efficiently. It can cause still births in baby pigs and slow growth rate in nursery pigs. Because of the susceptibility of unborn babies to carbon monoxide breathed by the mother, pregnant women are encouraged to work only in heated facilities that are free of carbon monoxide gas. The recommended maximum exposure limit to carbon monoxide is 50 ppm for pigs, poultry, calves and humans.

Carbon dioxide, while not considered dangerous at concentrations normally measured in enclosed animal facilities, can be used as a rough indication of overall air quality and effectiveness of a ventilation system. Concentrations of carbon dioxide that exceed 5000 ppm may indicate that too little fresh air is being supplied to the animals.