At what level of oxygen percentage is air considered deficient?

Air is considered deficient in oxygen when the concentration falls below 19.5%. Normal atmospheric air typically contains about 20.9% oxygen, which is the standard level for safe breathing. When the oxygen levels drop to 19.5% or below, individuals may start to experience difficulty in breathing, impaired judgment, and other health risks associated with oxygen deprivation. This threshold is particularly critical in hazardous materials situations, where low oxygen levels can pose serious risks to responders and others in the vicinity. Therefore, recognizing 19.5% as the limit is vital for maintaining safety in environments where hazardous materials may be present.