As a subject matter expert in industrial hygiene and safety, I can provide you with information on what percentage of oxygen is considered safe for human health and normal functioning. For humans to breathe comfortably and for life processes to occur efficiently, the oxygen concentration in the air needs to be within a certain range. Normal atmospheric air contains between 20.8 and 21 percent oxygen. This is the level at which the human body functions optimally. However, it's important to note that oxygen levels that are either too low or too high can be harmful. The **Occupational Safety and Health Administration (OSHA)** has established guidelines for oxygen levels in the workplace. According to OSHA, an atmosphere is considered oxygen deficient if it contains less than 19.5 percent oxygen. At these levels, the body can experience a range of symptoms from dizziness and shortness of breath to unconsciousness and asphyxiation. On the other side of the spectrum, an atmosphere is considered oxygen enriched if it contains more than 22 percent oxygen. High oxygen levels can lead to a condition called oxygen toxicity, which can cause seizures, respiratory issues, and damage to the central nervous system. In summary, for safety, it is crucial to maintain oxygen levels within the range of 19.5 to 22 percent, with the optimal level being around 20.8 to 21 percent for normal human health and functioning. read more >>

While normal atmosphere contains between 20.8 and 21 percent oxygen, OSHA defines as oxygen deficient any atmosphere that contains less than 19.5 percent oxygen, and as oxygen enriched, any atmosphere that contains more than 22 percent.read more >>