What is the required supervisory signal for water tank pressure below?

The correct answer, which specifies that a supervisory signal is required when water tank pressure falls below 40 PSI, is based on industry standards and regulations for monitoring water supply in alarm systems. This threshold is critical to ensure that adequate water pressure is maintained for fire protection systems, particularly in sprinkler systems where consistent pressure is necessary for efficient operation.

Establishing a supervisory signal at this level helps in early detection of potential issues that could lead to inadequate fire suppression capabilities. If the pressure drops below 40 PSI, it may indicate a problem such as a leak or pump failure that could compromise the firefighting system's effectiveness. Timely alerts ensure that corrective actions can be taken before the situation becomes critical.

The other pressure thresholds do not align with established standards for supervisory signals. Thus, they would not provide the appropriate level of monitoring to guarantee safety and reliability in fire protection systems.