Which factor is NOT a determinant of TUC/EPT?

• A. Altitude
• B. Physical activity
• C. Lifestyle
• D. Oxygen mask color

Answer: (D)

Time of Useful Consciousness (TUC) and Effective Performance Time (EPT) are determined by how long the body can function under hypoxic conditions before oxygen deficiency impairs performance. The big influences are altitude and how hard the body is working. At higher altitudes, the partial pressure of oxygen drops, so TUC/EPT shorten because there’s less oxygen available for the brain and tissues. When you’re physically active, your metabolic rate goes up, so your tissues consume oxygen faster, which also shortens TUC/EPT. Lifestyle factors—like overall fitness, cardiovascular health, and smoking status—affect how efficiently you use oxygen, so they can lengthen or shorten your usable time depending on the individual.

The color of the oxygen mask has no impact on oxygen delivery or physiological response; it doesn’t change how much oxygen you receive or how your body responds, so it does not determine TUC/EPT.