What are the most common confined space gases?

The most common gases found in confined spaces include carbon monoxide, hydrogen sulfide, methane, and oxygen-deficient atmospheres. Carbon monoxide is produced by incomplete combustion, while hydrogen sulfide often originates from decaying organic matter or industrial processes. Methane is typically associated with natural gas and can accumulate in certain environments. Oxygen deficiency can occur due to displacement by other gases or consumption by chemical reactions, posing significant safety risks.