Final answer:
A firefighter with symptoms of light-headedness, disorientation, and rapid fatigue is likely experiencing hypoxia, an oxygen deficiency due to low partial pressure of oxygen, which can severely impair health.
Step-by-step explanation:
A firefighter experiencing symptoms such as light-headedness, disorientation, and rapid fatigue could be suffering from hypoxia, which is a deficiency in the amount of oxygen reaching the body's tissues. The partial pressure of oxygen is crucial for maintaining energy homeostasis in the body. Hypoxia can occur if a person is breathing air with a low partial pressure of oxygen (below 0.16 atm), which could impair coordination and judgment, and can be severely detrimental to health if the partial pressures fall below 0.06 atm. The symptoms mentioned can also align with conditions such as acute mountain sickness (AMS), which presents similar symptoms, and is a result of the low atmospheric pressure at high altitudes decreasing the oxygen levels in the blood and tissues. Therefore, a firefighter showing such symptoms most likely has A. an oxygen deficiency.