How does the high-high level alarm signal on a Type III operating storage tank?

The correct answer highlights the specific response of the alarm system for a Type III operating storage tank when high-high level conditions are detected. A flashing primary control panel (PCP) indicates a visual alert that draws immediate attention to the situation. This is crucial because high-high levels may signal an overfill condition, which poses risks for both safety and environmental contamination. The resonating horn amplifies the alert, ensuring that personnel in the vicinity can hear the alarm clearly, even in noisy environments.

The distinction between a resonating horn and other types of sounds is important, as it suggests a specific auditory signal designed to command urgency. This combination of visual and auditory alerts ensures a prompt and effective response to mitigate any potential hazards associated with high levels in the tank.