In our blog article “Everything you need to know about water mist,” we discussed the operation, types and applications of water mist systems.

In this article, we will delve into UNI EN 14972, the European standard on water mist systems.


Introduction to the UNI EN 14972 standard

EN 14972-1:2020 was published on December 23, 2020 replacing the European technical specification in force until then (CEN/TS 14972:2011). UNI has fully implemented this European standard and as of February 25, 2021, it became part of the Italian normative body (UNI EN 14972-1:2021).

The standard is structured in 17 parts, of which Part 1 specifies the requirements and provides information on the design, installation, controls and maintenance of all types of water mist systems (cylinder or with pumping unit, with automatic or open nozzles).

Parts 2 through 17 represent the fire test protocols for which the standard applies.

A major change introduced in the standard is certainly the clear definition, for the applications covered by the test protocols, of the minimum requirements in terms of discharge duration time and, in the case of water mist systems with automatic nozzles, operating area. The standard devotes an entire annex (B) to the topic of operating area for systems with automatic nozzles, presenting a number of calculation examples.


Main Novelties of UNI EN 14972-1:2021

Definition of Operating Area

For automatic nozzles:

  • Maximum area over which, for design purposes, water mist nozzles are assumed to activate in the event of a fire;

For open nozzles:

  • All nozzles included in a section


For automatic nozzle applications, the system sizing requirement is discriminated not only by the determination of the operating area, but also on a minimum quantity of automatic nozzles, indicated in the standard in the specific case and referred to the specific test protocol.

The latter requirement highlights a departure from the sizing logic of conventional sprinklers that was very well established in the 2011 version.

For example, with regard to the protection of offices, restaurants, hotels, libraries, etc., falling under the UNI EN 14972 part 3 test protocol, and basically falling under fire hazard class OH1 (ref. UNI EN 12845:2020) in addition to the determination of the operating area, the sizing of the pumping unit and water reservoir must be carried out considering the intervention of a minimum number of automatic water mist nozzles equal to 6, regardless of the spacing and flow rate of the nozzles tested during fire testing.


Hydraulically most favorable/unfavorable area

Hydraulically Most Favorable Zone

Area of operation for which water flow is at maximum for a specified pressure, measured at the control valve or pump assembly.

Hydraulically Most Unfavorable Zone

Area of operation for which the system pressure, measured at the control valve or pump assembly, must be at its maximum to achieve the specified flow rate.

Innovations in water supplies

Compared with the previous version, another important innovation concerns the possibility of designing water supplies with reduced capacity, obviously guaranteeing their make-up to ensure the flow rate required by the water mist system. In the case where this replenishment is by electrically powered equipment, this equipment must be monitorable, redundant, and supplied by emergency power line.

If designing with reduced water reserve, the following parameters must be met:

  • 5 min pumping system operation time if the system discharge time is less than 30 min;
  • 10 min pumping system operation time if the system discharge time is more than 30 min.

The following types of supplies are defined as acceptable:

  • aqueduct,
  • cylinders,
  • pressure or gravity tanks,
  • tanks/wells/tanks with suction pumps.

In addition, where the fire strategy requires water supplies with a higher degree of reliability and availability, the standard considers the alternatives acceptable:

  • in the case of aqueducts, this must be connected to the circuit at the two extreme points,
  • in the case of pressure or gravity tanks, these must not be of reduced capacity,
  • in the case of tanks/wells/tanks with suction pumps, these must be redundant.

Compared with the previous 2011 version, however, the two annexes pertaining to the determination measure of water droplet size and mechanical and functional stress tests on nozzles, respectively, have been removed.

For what applications can water mist systems not be used?

Water mist systems are suitable for many applications but should not be used where the application of water may cause additional risks.

They should not be used for direct application to liquefied gases at cryogenic temperatures (such as liquefied natural gas), which boil violently when heated by water.

Materials that react with water include: reactive metals, such as lithium, sodium, potassium, magnesium, titanium, zirconium, uranium and plutonium; metal alkoxides, such as sodium methoxide; metal amides, such as sodium amide; carbides, such as calcium carbide; halides, such as benzoyl chloride and aluminum chloride; hydrides, such as lithium aluminum hydride; oxyhalogenides, such as phosphorus oxybromide; silanes, such as trichloromethylsilane; sulfides, such as phosphorus pentasulfide; cyanates, such as methylisocyanate.


Useful recommendations for the area to be protected

Ventilation in the protected area

Whenever possible, the ventilation system should be turned off before the system goes into operation. Where this is not possible, the air velocity should be within the limits specified by the DIOM manual (discussed in the next section).

Fuel and other combustibles used in the protected area.

During a fire, provision must be made to discontinue any additional fuel supply as part of emergency firefighting procedures, except for the minimum supply for emergency operating systems. This point should also be considered when specifying the period of operation.

Supply of equipment in the protected area

Normally, high-voltage supplies for equipment in the affected area should be turned off when the water mist system is activated or when a fire is detected. Exceptions are minimum supplies for emergency operating systems. Where this is not possible, provisions must be in accordance with the DIOM manual.


The crucial role of the DIOM

Another important change in the new version of the standard is the introduction of the DIOM (manufacturer’s design, installation, operation and maintenance manual).

This is a design, installation, operation and maintenance manual that must be delivered for each water mist system and must be specific to each fire test protocol.

The DIOM manual must be dated and identifiable with a reference number or date and revision status to clarify the current version.

The information in it must include at least the following, where applicable:

(a) type and identification of the system;

(b) applicable occupancies with any limitations;

(c) description of hazards;

(d) ventilation limitations and environmental conditions;

(e) area and room limitations;

(f) requirements on fire-resistant separation;

(g) design parameters:

  • Nozzle type and unique model identification,
  • number of operating nozzles or area of operation,
  • additives (if used),
  • minimum operating pressure,
  • specific pressure for automatic startup of the first pump unit when pressure drops in the water mist system,
  • minimum flow rate at the nozzle and maximum pressure at the nozzle,
  • minimum and maximum ceiling height,
  • minimum and maximum volume or area,
  • minimum and maximum distance between nozzles,
  • nozzle orientation, installation and placement parameters,
  • requirements regarding obstacles (e.g., minimum distance from beams, spray obstacles),
  • type of fire detection system (if used in the fire test),
  • minimum/maximum distance of the thermal release element from under the ceiling,

(h) list of critical components compatible with the water mist system (e.g., nozzles, priming, signaling, and valves),

(i) minimum requirement for water and/or misting gas quality,

(j) hydraulic calculations or other sizing methods (e.g., pre-engineered systems, system accumulators],

(k) additives (if applicable):

  • specific type;
  • specific concentration;
  • method of mixing the additive with water;
  • method of handling the additive/water mixture during the life cycle;
  • material safety data sheet of additives;
  • explanation of the effects of the additives;

(l) any constraints critical to the operation of the water mist system (e.g., information on nozzle cover plates, guards, and accessories such as cover plates),

(m) for each application list the associated fire test protocol and test report reference.


Maintenance of water mist systems: how to do it?

Water mist systems are normally stand-by systems, which are activated the moment an incident occurs.

For this reason, they are susceptible to failure if their efficiency is not kept active at all times through scheduled maintenance and testing activities.

Often maintenance activities are considered a heavy burden, or difficult because of the type of some facilities, and therefore they are not given due importance.

Or they are carried out by personnel who are not properly trained or without specific experience of the plant to be maintained.

Since these plants can remain even several years in a stand – by situation, the lack of or ineffective maintenance can generate inefficiencies at the time of need.

These inefficiencies result in:

Failure to deliver
Delivery deviating from the design parameters

Maintenance must be carried out in accordance with the directions expressed in the DIOM and in compliance with the standard.

For domestic and residential systems, verification and maintenance functions can be carried out by the user. At least once a year, or more frequently when required by the DIOM manual, all systems should be thoroughly inspected and tested for proper operation by competent personnel.

It is with this in mind that the Normator, in the current edition, has intensified its maintenance activities by defining a detailed program of all interventions that can minimize the risk of missed or inefficient.


Weekly Verification of all pressure gauges located on main trunks and cylinders.
Pressure of dry lines of preaction systems must not be less than 1 bar per week
Verification of all water tank levels
Correct position of all shut off valves
Checking whether the alarm on each valve is working
Pump test
Check and record unit starting pressure
Check oil and lubricant levels
Verify oil pressure
Diesel Engine Test
Keep the engine running for 20 min
Stop the engine and immediately activate it using the test button
The water level of the primary level of the closed circuit should be checked
Check oil pressure engine coolant temperature, check hoses, check for leaks.
Monthly Verify proper operation of heating systems
Check batteries (electrolyte and acid level)
Quarterly Check the pumping unit with each of its valves
Start the pumps and check that the pressure is not lower than the nameplate values
Carry out sequences of multiple pump activations
All secondary electrical supplies must be tested
All shut-off valves activated and closed appropriately
Simulate nozzle activation to verify proper operation of alarm signals, discharge tripped, and that pump starts automatically
Verification of spare parts
Semiannual Verification of dry valves and deluge valves
Verification of the detection and alarm system
Annual Risk verification – changes to structures or fire load
Visual inspection of nozzles
The pumping unit should be tested at full load (using a dedicated line )
Check fail-to-start according to 12845 for diesel engine
Check water fill valves in tanks
Verify pumping unit filters are clean
Verify piping and brackets are free from corrosion and mechanical damage
Verify grounding of piping
Verify degree of filling of tanks and cylinders (< 5% of charge/pressure)
Verify signal transmitters remotely
Visual inspection of system (if doubtful of leaks proceed to line pressing)
Triennial All tanks should be examined externally for corrosion
Check all shut off and control valves
Quinquennial Two nozzles per section should be tested for:
intervention temperature
thermal response
Decennial Cleaning of all water tanks
Pipe flushing

Maintenance personnel must have knowledge and experience of the regulatory framework of the facilities on which they are to work, as well as practical knowledge and training of the components of the facilities.


Who can perform maintenance on water mist systems?

In order to perform maintenance on a water mist system, the maintenance technician must have:

  • Certificate of qualification issued by the Fire Department.
  • Training certificate issued by the manufacturer of the water mist system.

In the absence of either certificate, the maintenance technician is not authorized to perform maintenance on a water mist system.

With regard to systems for residential use, at least once a year, the system must be maintained according to the manufacturer’s instructions by a company authorized by the manufacturer.

The installer must provide the user with a maintenance program for the system and components in accordance with the manufacturer’s design and installation manual.

The program must include instructions on actions to be taken in case of failure.


Qualified fire maintenance technician: the Controls Decree and UNI EN 14972-1:2021

On Sept. 25, 2021, the “Controls Decree” was published, which regulates the “General criteria for the inspection and maintenance of facilities, equipment and other fire safety systems, pursuant to Article 46, paragraph 3, letter a) item 3, of Legislative Decree No. 81 of April 9, 2008.”

Among the relevant points of the Decree, drafted by the Ministry of the Interior in consultation with the Ministry of Labor and Social Policy, is the introduction of the figure of the qualified maintenance technician.

Point 6 of Annex 2 of the decree mentions:

The National Fire Department shall issue the certificate of qualified maintenance technician following positive assessment of learning outcomes.


What are the tasks and activities that the qualified maintenance technician can and must perform?

  • Perform documentary checks;
  • Perform visual and component integrity checks;
  • Perform functional, manual or instrumental checks;
  • Perform the maintenance activities required as a result of the outcome of the checks performed;
  • Make records of activities performed in paper or digital form;
  • Perform maintenance activities in accordance with standards and procedures related to occupational health and safety and environmental protection;
  • Relate with the employer (or person in charge of the activity) regarding control and maintenance activities;
  • Coordinate and supervise maintenance activities.

Component testing protocols and certification

In the new edition of UNI EN 14972, test protocols have been designed as stand-alone standards, and at present 16 test protocols have been identified (not yet all published).

Detail of the test protocols

Part 2: Commercial area test protocol for systems with automatic nozzles; An inspection report including recommendations must be filed with or by the owner. A complete maintenance program, including the user’s inspection and service program, must be provided at the time of acceptance testing. The design, installation, and commissioning records must be retained by the system user so that they are available for any inspection of the water mist system. At least once a year, the system must be maintained according to the manufacturer’s instructions by a company authorized by the manufacturer The installer must provide the user with a maintenance schedule for the system and components in accordance with the manufacturer’s design and installation manual.
The program must include instructions on actions to be taken in case of failure.
Part 3: Test protocol for offices, classrooms, and hotels for systems with automatic nozzles;
Part 4: test protocol for non-storage occupancies for systems with automatic nozzles;
Part 5: Test protocol for garages for systems with automatic nozzles;
Part 6: Test protocol for suspended ceilings and subfloors for systems with automatic nozzles;
Part 7: Test protocol for low-risk commercial occupancies for systems with automatic nozzles;
Part 8: Test protocol for machines in enclosures greater than 260 m3 for systems with open nozzles;
Part 9: Test protocol for machines in enclosures not exceeding 260 m3 for systems with open nozzles;
Part 10: Test protocol for protection of atria with side nozzles for systems with open nozzles;
Part 11: test protocol for cable tunnels for systems with open nozzles;
Part 12: test protocol for commercial fryers for systems with open nozzles;
Part 13: test protocol for wet benches and other similar equipment for systems with open nozzles;
Part 14: test protocol for combustion turbines in enclosures greater than 260 m3 for systems with open nozzles; and
Part 15: Test protocol for combustion turbines in enclosures not exceeding 260 m3 for systems with open nozzles;
Part 16: Test protocol for industrial oil cookers for systems with open nozzles; and
Part 17: Test protocol for residential occupancies for systems with automatic nozzles.


Certifications and components: what are they?

EN 54 – Fire detection and fire alarm systems.

When system activation depends on a detection system, all parts of the detection system shall comply with the relevant parts of EN-54.

UNI EN 12094 – Components of gas extinguishing systems.

Part 1 : electrical automatic control device and delay devices.

Part 2: non-electrical automatic control device and delay devices

Part 4: valves and actuators

Part 8: connectors

Part 10: pressure gauges and pressure switches

UNI EN 12259 – Components for sprinkler and water spray systems.

Part 1: sprinklers

Part 2: dry alarm valves

Part 3: wet alarm valves

EN 17450 -1: Components for water mist systems – Filters

EN17451 : Automatic sprinkler systems – design , installation and commissioning pumps

EN 50342: lead-acid starter batteries.

EN 60529: protection (IP grade)

EN 60623: secondary batteries

Directive 2014/68/EU – Pressure Equipment.

In cylinder systems, all pressure parts must comply with the PED Directive

Directive 2010/35/EU – Transportable pressure equipment

In cylinder systems, cylinders containing pressurized gas shall be marked


Documents accompanying the systems

Documentation for design acceptance, installation and commissioning.

Documentation for acceptance of design, installation, and commissioning must include at least the following:

  1. complete design information, including system identification, type and application, and risk limits
  2. system design parameters and hydraulic calculations (water or other medium)
  3. requirements for commissioning and acceptance:
    – hydrostatic test results;
    – that the necessary flushing and cleaning has been carried out so that the piping is free of debris that could cause nozzle blockage,
    – results of functional tests,
    – the installed system is in accordance with the documentation (drawings and calculations),
  4. complete description of the functional system (to include operating sequence, delays, break functions, maintenance switches, and all other relevant items),
  5. location and identification of nozzles,
  6. schematic diagrams of the entire system, including all point-to-point connections within the entire system.
  7. plan and sectional views of the protected area with the layout of:
    – divisions, dimensions and locations of the zones,
    – all piping, nozzles, and all hooks and supports,
    – all alarm and control system devices,
    – all controlled devices such as dampers, valves, etc. ,
    – all warning and instruction signs,
    – isometric view of the complete system,
    – plans including full details of all piping and equipment in the system,
    – Evidence that the hazard is within the scope of the DIOM manual,
    – system line diagrams and parts lists,
    – drawings or data sheets, or both for component identification.

If field conditions require a change from the approved documentation, the change must be recorded in the documentation.

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