Entering a permit space can prove fatal for an employee when the oxygen level is below what percentage?

The correct answer, 19.5%, is significant because it reflects the minimum oxygen level required to maintain a safe working environment within a confined space. An oxygen concentration below this threshold indicates that the atmosphere may be considered oxygen-deficient and poses an immediate risk to life and health.

Typically, an atmosphere that is below 19.5% oxygen can lead to symptoms ranging from impaired judgment and coordination to unconsciousness and death, depending on how low the levels drop. Normal atmospheric air contains about 20.9% oxygen, and levels below 19.5% should trigger preventive measures, including atmospheric testing and the potential implementation of safety protocols like ventilation or the use of supplied breathing air.

The other options represent oxygen levels that are dangerously low but do not serve as the threshold for initiating caution or emergency procedures in most regulations and safety guidelines. Therefore, it's essential to recognize 19.5% as the critical level that marks the transition from safe to potentially life-threatening conditions in a confined space environment.