What is a requirement for Self-Contained Breathing Apparatus (SCBA) usage?

Wearing a Self-Contained Breathing Apparatus (SCBA) when oxygen levels drop below 19.5% is a critical safety requirement. This is because oxygen levels at or above 20.9% are considered normal for safe breathing conditions. When the oxygen concentration falls to 19.5%, it may lead to symptoms of oxygen deficiency, such as dizziness or impaired cognitive function, which could adversely affect a person's ability to work safely. Therefore, SCBA usage is mandated in environments where the oxygen level is at or below this threshold, ensuring adequate respiratory protection against potentially harmful, low-oxygen atmospheres.

Other options present different contexts that do not align with the established safety regulations regarding SCBA use, such as specifying levels of oxygen that are not within the safety margin or wrongly limiting usage based on job classification or the location of work. Only the guideline of wearing an SCBA in environments with oxygen below 19.5% correctly reflects the safety standards necessary to safeguard workers in hazardous conditions.