*Question E0A04:
When evaluating a site with multiple transmitters operating at the same time, the operators and licensees of which transmitters are responsible for mitigating over-exposure situations?*  

*Correct Answer is  C: Each transmitter that produces 5 percent or more of its MPE limit in areas where the total MPE limit is exceeded*  

### AI Response: (may contain errors)  

To understand the responsibilities of operators and licensees regarding over-exposure situations at a site with multiple transmitters, we need to focus on the concept of Maximum Permissible Exposure (MPE) limits.

### Correct Answer: 
**C: Each transmitter that produces 5 percent or more of its MPE limit in areas where the total MPE limit is exceeded.**

#### Explanation:
- The Federal Communications Commission (FCC) regulations state that if a transmitter contributes 5% or more of the MPE limit in an area where the total MPE limit is exceeded, the operator is responsible for mitigating the exposure. This ensures that all operators are accountable for their contributions to potential over-exposure situations.

### Why the Other Choices are Incorrect:
- **A: Each transmitter that produces 20 percent or more of its MPE limit in areas where the total MPE limit is exceeded.**
  - This choice is incorrect because the threshold for responsibility is set at 5%, not 20%. A higher threshold would allow more exposure without accountability.

- **B: Each transmitter operating with a duty cycle greater than 25 percent.**
  - This option is misleading as it focuses on duty cycle rather than the percentage of the MPE limit. Duty cycle alone does not determine responsibility for over-exposure.

- **D: Each transmitter operating with a duty cycle greater than 50 percent.**
  - Similar to option B, this choice incorrectly emphasizes duty cycle. The responsibility is based on the percentage of the MPE limit, not just the duty cycle.

### Useful Rules of Thumb:
- **MPE Calculation**: The MPE limits are defined for different frequencies and exposure durations. Operators should always refer to the specific MPE tables provided by the FCC.
- **Mitigation Responsibility**: If your transmitter contributes 5% or more of the MPE limit in an area where the total exceeds the limit, you must take action to mitigate exposure.

By understanding these concepts, you can better prepare for questions related to MPE and operator responsibilities on the Extra Class exam.