What pressure level triggers the low air alarm?

The correct choice is 5 psi under system air pressure, as this is the standard threshold that triggers the low air alarm in a sprinkler system. This level is set based on industry standards and safety protocols to ensure that the system maintains adequate pressure for proper operation. If the air pressure drops to this level, it indicates a potential issue with the air supply or the integrity of the system, prompting immediate attention to prevent further complications, such as losing system reliability or effectiveness in fire suppression.

The choice of 5 psi is crucial because it provides a buffer above the normal operational pressure that allows for early detection of pressure drops. It serves as a proactive measure to maintain safety within the system, enabling timely maintenance or repairs to be conducted before reaching a critical level that could compromise the sprinkler system's function.