Mixed-use fire hydrant systems: Yes, they are permitted in accordance with the provisions of UNI 10779. Below is a detailed response, including the conditions, restrictions, and practical implications mentioned in the referenced standard.*
Table of Contents
When mixed feeding is permitted (UNI 10779)
A mixed-source supply toa fire hydrant network is permitted in accordance with the provisions of UNI 10779. In other words, it is not a “universally applicable” solution: it must be evaluated on a case-by-case basis and is permitted only under the specific conditions set forth in the standard referenced in the text.
The key question is not just “Is it possible?”, but “Under what conditions is it acceptable?”: UNI 10779 is cited as a direct reference for determining when mixed feeding can be adopted.
Requirements: Supported Activities and Configurations
Mixed feeding is considered acceptable in the following cases:
- Only for activities classified as Hazard Level 1.
- If only the internal protection system is installed, with no above-ground or underground UNI 70 fire hydrants.
These two points must be considered together: it is not enough simply to “have a network of fire hydrants”; what matters is the declared hazard level and the configuration of the fire protection system (internal protection is required, but without the external UNI 70 fire hydrants specified in the text).
Connection to the building’s main water supply
For the cases indicated (hazard level 1 and internal protection only), the text clarifies that the water supply may be provided as a branch from the building’s general water supply system.
This passage is key because it describes the logic behind “mixed-source water supply”: the fire protection system is not supplied by a completely separate line, but is drawn from the general water supply, provided that additional requirements (outlined in the next section) are met.
Conditions Affecting the Water System’s Flow Rate, Pressure, and Reliability
In addition to general eligibility, the text requires compliance with additional conditions, including:
- The system’s flow rate and pressure performance must take into account the combined requirements of the fire protection and domestic water systems.
- A certificate of reliability from the water utility must be requested.
Therefore, the inspection does not concern only the fire protection system “in isolation,” but must also take into account domestic water use, because the demand is explicitly defined as combined.
Check Valve and Independence of the Fire Protection System
The text introduces two very specific functional requirements:
- Install a check valve or other equivalent device to prevent water from flowing back from the internal plumbing system into the external water supply system.
- Ensurethe complete independence of the fire protection system starting from the power supply point, with regard to the Fig. A1 as set forth in Appendix A of UNI 10779.
In practice, the power supply may be “shared,” but the fire suppression system must remain independent from the power supply point onward, and backflow to the outside must be explicitly prevented by a device equivalent to a check valve.
If the required pressure is not reached: pump unit
The text also addresses the situation in which the required pressure at the points of use is not achieved: in that case, it will be possible (and recommended) to install a pump unit.
This instruction should be interpreted as an operational response to a test result: first, check whether the pressure required by the loads is met; if it is not, the pump unit is activated to make up the difference and meet the pressure requirement.
Pumps and Pump Rooms: What Changes with UNI EN 12845 and UNI 11292
In the case of mixed-feed systems, the text specifies that the pumping unit is not required to comply with the requirements of UNI EN 12845, citing section A2 of UNI 10779:
- “In the case of mixed feeding where the above requirements are met, the provisions set forth in section A.1 do not apply.”
And we are reminded of what point A1 states:
- “The relevant requirements of UNI EN 12845 apply to the construction of water supply systems, with the following additions.”
The implication stated in the text is clear: in this case, UNI EN 12845 does not apply to the pumps, and consequently, the room does not have to comply with UNI 11292 either.
Conclusions
A mixed-use hydrant network is permitted if it falls within the specified cases (hazard level 1 and internal protection only, without external UNI 70 fire hydrants) and if the conditions regarding combined demand, water supply system reliability, backflow prevention, and independence from the supply point are met. If the required pressure is not achieved, a pump unit may be necessary, with the implications specified in UNI EN 12845 and UNI 11292.
