What must sound for at least 20 seconds before CO2 is released in a fixed system?

In a fixed CO2 fire suppression system, a warning alarm must sound for at least 20 seconds before the CO2 is released. This is crucial as it provides a warning to personnel in the vicinity, allowing them to vacate the area and ensure their safety prior to the activation of the system. The alarm serves as a critical safety measure, notifying people of the impending discharge of CO2, which can displace oxygen and create a hazardous environment.

This procedure is established to minimize the risk of injury or exposure to the high concentrations of CO2 that would follow the activation of the suppression system. A warning alarm is specifically designed for this purpose, offering an audible signal that alerts individuals to prepare for potential evacuation without causing panic.

In this context, while the fire alarm, evacuation alert, and safety alarm all involve critical safety protocols, they do not serve the same specific purpose as the warning alarm, which is dedicated to alerting inhabitants of the impending CO2 release.