What percentage of oxygen by volume defines an oxygen deficient atmosphere?

An oxygen-deficient atmosphere is defined as one that contains less than 19.5% oxygen by volume. This threshold is significant in safety practices, particularly in confined spaces, because 19.5% is the minimum oxygen concentration considered safe for human breathing. Levels below this can lead to symptoms of oxygen deficiency, such as dizziness, confusion, and, in severe cases, unconsciousness or death due to asphyxiation.

In various industrial and safety guidelines, maintaining oxygen levels at or above 19.5% is crucial for ensuring the safety and health of workers in environments where oxygen levels might be compromised. This standard is established by organizations such as OSHA (Occupational Safety and Health Administration) to safeguard workers against the risks associated with low oxygen environments.

Other options presented do not accurately reflect the widely accepted standard for an oxygen-deficient atmosphere. The specific value of 19.5% has been identified specifically to prevent health risks associated with low oxygen environments.