Final answer:
A permit space is dangerous and potentially fatal for an employee if the oxygen levels fall below 19.5% or rise above 23.5%, as these levels can lead to hypoxia or hypoxemia.
Step-by-step explanation:
Entering a permit space can prove fatal for an employee when the O2 level is below 19.5% and above 23.5%. These levels are important for keeping a balance in the atmosphere of the confined space to ensure safety and avoid hypoxia or hypoxemia, both conditions of low oxygen in the body that can lead to serious health complications or death. Breathing air with a partial pressure of oxygen below 0.16 atm can impair coordination and judgment, and below 0.06 atm can be quickly fatal. Safety engineers are vigilant about this risk and measures are taken to prevent such hazardous exposure.