Monitoring the level of the fire protection water reserve: Yes, it is required to provide a method for checking/indicating the level and managing the corresponding alarm, as specified in UNI EN 12845. In this response, we outline the regulatory requirements mentioned and the most commonly used practical solutions.
Table of Contents
What does UNI EN 12845 require in section 9.3.2.1?
UNI EN 12845 addresses this issue in section 9.3.2.1, stating that, with the exception of open basins, tanks must be equipped with a water level indicator that is readable from the outside.
In practice, the requirement isn’t just to “know” that there is water: we need a system that makes it possible to clearly verify the water level in the cistern or tank from the outside.
What do APP. H and APP. I (Table I.1) add?
In addition to the “visual” requirement in 9.3.2.1, in the APP. H (Fluid Levels) All critical fluid levels, including water storage tanks, must be monitored so that the water level does not fall more than 10% below the nominal fill level.
Finally, in the APP. I , in Table I.1 (list of alarms to be transmitted), the liquid level (including the water reserve level) is listed among the Type B alarms (technical alarms) that must be monitored and transmitted to a manned area.
Solution 1: Level indicator visible from the outside + level switch
To comply with the requirement in 9.3.2.1, a simple level indicator (such as the one mentioned in the example) may be used.
This indicator must be accompanied by a level switch (such as a float switch) capable of triggering an alarm contact when the level specified by the APP. H (that is, before the decline exceeded 10% from the nominal level).
With this combination, you get:
- external level reading (indicator);
- generation of the alarm contact (level switch/float switch);
- willingness to monitor and trigger the alarm as required.
Solution 2: Visual indicator equipped with electrical contacts
Alternatively, you can install a visual indicator that is already equipped with electrical contacts.
In this case, the indicator’s contacts can be used directly as alarm contacts and routed to a manned station, in accordance with the provisions regarding technical alarms (APP. I, Table I.1) and the indication threshold specified in APP. H.
The practical advantage of this option, compared to the “indicator + float” solution, is that the visual indicator and the contacts are integrated into the same device, while still achieving the goal of displaying the level and triggering the alarm.
Solution 3: Submerged level sensor with a 4–20 mA signal
According to the description, the simplest method for monitoring the level of the fire protection water reservoir and triggering the required alarm is to use a level sensor submerged in the reservoir that provides a 4–20 mA signal proportional to the free-surface level.
This setting provides a “continuous” (proportional) signal, which is useful both for level indication and for managing the required alarm threshold (APP. H), without compromising the objective: ensuring legible display and alarm transmission as specified in APP. I.
Connection to the pump control unit and alarm transmission
The sensor can be connected to the electronic control unit of one of the main fire pumps, so as to:
- always display the tank level on the screen (in accordance with the requirement in 9.3.2.1 regarding level indication);
- be able to manage and transmit the low-level tank alarm, as required by the other sections referenced (APP. H for the indication threshold and APP. I/Table I.1 for the alarm to be sent to the manned area).
In summary: level indication and alarm generation/transmission are two sides of the same operational requirement.
Which Solution to Choose (Based on What You Actually Need)
The three options described lead to the same goal: meeting the requirements cited (9.3.2.1, APP. H, APP. I) without unnecessarily complicating the system.
In terms of functional logic:
- If an immediate visual check is the main requirement,the externally readable indicator is the basis;
- If an alarm is also needed, contacts are required (from a level switch/float switch or built into the indicator);
- If you want direct and proportional monitoring, the submersible 4-20 mA sensor provides a dedicated signal that can be processed by the control unit, while keeping both the display and the alarm active.
Conclusion
For a tank used as a fire protection water reserve, a system must be provided that allowsthe level to be read from the outside (UNI EN 12845, 9.3.2.1) and that enablesa low-level alarm to be generated and transmitted (APP. H and APP. I/Table I.1) to a manned area. Solutions may be simple (gauge + float), integrated (gauge with contacts), or signal-based (4–20 mA sensor).
