At first glance, the system would be classified as an extinguishing system with a gas extinguisher and the best sprinkler system. However, it is neither gas nor water, it is mist. By using the dynamic pressure of 140 bar and special nozzles, we are able to disperse water droplets with a diameter between 50 and 120 micrometers at very high speed, which ensures good penetration into the centre of the fire – to the flame – even in adverse conditions, for example during heavy winds or intense ventilation (a system for smoke and heat removal, ventilation in tunnels). The smaller the water droplets, the greater their total effective surface area: cooling and inerting. Reducing the diameter of the water droplets by 20x increases their total area by 400x and their number by 8000x.

How is the water mist used for extinguishing?

Extinguishing system with water mist in a tunnel

Extinguishing system with water mist in a tunnel

The water mist extinguishes or limits the fire in three ways: by cooling the room and the equipment, by blocking radiation and by locally reducing the oxygen concentration. Unlike gas extinguishers where we have to consistently follow the instructions for use, fine water mist is completely safe. People can stay in the room even while the fire is being extinguished. Its significant advantage over the sprinkler system is that only a small quantity of water leaks out.

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When to choose the water mist extinguishing system?

Protection of airports, libraries, industrial machinery etc. The water mist system has been implemented, tested in practice and integrated into a variety of different systems and facilities. Since the electric conductivity of water mist is poor, it can also be used to extinguish fire in environments containing devices under voltage, even in data and communication centres.

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For small systems, the price of installing a gas system is lower than the price of a high-pressure mist system, however the price of water mist systems is gradually decreasing due to its increased use. High-pressure mist systems do not require tight spaces, people can stay in the room even while extinguishing takes place, the extinguishing time is longer, and the installation price is lower for large systems.

Construction of a high-pressure mist system

A high-pressure water mist system consists of four basic parts: water storage, high-pressure generator, distribution piping system and special nozzles.

Water mist - extinguishing nozzle

Water mist – extinguishing nozzle

The water storage is a cylinder or a group of cylinders containing clean water in small systems, and a water tank in larger systems. In some cases, the system can be fuelled directly from a reliable water supply system. Clean water is used, which must be filtered by a 100 filter and must not contain too much chlorine or other additives. The use of foaming agents and other substances, which appear to increase the extinguishing efficiency, is prohibited.

The high-pressure generator is a small cylinder with nitrogen or air with a nominal pressure of 200 bar in smaller systems which directly pushes the water towards the nozzles. In medium-sized systems, the compressed nitrogen or air in the cylinders powers special high-pressure pumps which in turn push the water towards the nozzles. Large capacity high-pressure pumps driven by electric or diesel engines are required for the largest systems.

The distribution piping system consists solely of high-pressure stainless pipes. The pipes are not welded together; they are connected with high-pressure couplings. Due to the very low water consumption, the external diameters of the pipes are small, from 12 mm onwards, which allows for bending and precise modification to the configuration of the facility. Stainless materials prevent rust in pipelines which usually appear in sprinkler systems. A small quantity of water and its purity allow live testing with the discharge of water mist without harm to the room and objects under protection.

Special nozzles for open deluge systems consist of the body with a 300 filter, where special mist creation nozzles are inserted. Nozzles for high-pressure sprinkler systems additionally have a fast performance thermal element.

The water mist extinguishing system at the Ljubljana Jože Pučnik airport

The passenger terminal T-2 at the Ljubljana Jože Pučnik Airport is one of the most important investments in Slovenia in recent years. In agreement with the investor, the author of the architectural design and fire safety experts in Slovenia and abroad, we decided for a technology of fire protection which is relatively new for Slovenia: extinguishing with high-pressure water mist.

Aerodrom_Ljubljana_36

Why did we choose high-pressure water mist?

The main reasons for our decision are as follows:

  1. Minimum water consumption – a reservoir with a capacity of 22 m3 is sufficient for 5000 sprinklers (which is also the approximate final figure for the second expansion phase). This is a big saving in comparison with the required “Olympic pool” for a conventional sprinkler system (the calculated quantity of water needed for this facility is approximately 8 times smaller). Both systems must operate for 60 minutes according to the requirements of standards.
  2. Excellent extinguishing properties in three ways: by cooling the room and equipment, by blocking radiation, by locally reducing the oxygen concentration; all of this is a result of the use of extremely tiny water droplets with sizes between 50 and 120 µm.
  3. High speed water droplets from the high-pressure system ensure good penetration into the fire and reduce the impact of ventilation on the distribution of water mist.
  4. Fine water mist is safe: people can stay in the room even during extinguishing.
  5. Fine water mist is safe for your property and is not electrically conductive: only a small quantity of clean water leaks out. This feature also allows live testing of the system without the risk of harmful consequences.
  6. The use of stainless steel pipes of small diameters and special high-pressure couplings makes the installation easy, flexible and weld-free.
  7. Fine water mist causes minimal damage after the fire and allows you to immediately continue your business activities. There are no floods or soaked objects as with conventional sprinklers.
  8. An additional good characteristic that no other extinguishing system has is that smoke and fire products are washed out. The concentration of toxic gases and aggressive compounds, produced by the fire, is thereby dramatically reduced.
  9. We decided to use the HI-FOG system, manufactured by Marioff, because it demonstrated high reliability and because they have a number of important references for marine and land applications worldwide in addition to over 6000 natural size test fires and over 100 attestations.

The starting point for the construction of the extinguishing system was a fire protection study carried out by CPZT (Bojan Grm, Msc.) from Radovljica, the architectural and construction proposals drawn up by EKO ART (architect Vladimir Koželj) from Ljubljana, arrangements with investors, attestations, technical data sheets and other technical documentation by the equipment manufacturer Marioff from Finland as well as the applicable standards and regulations, in particular NFPA 750, NFPA 13, VdS CEA 4001.

The system is based on a high-pressure pump in the basement of the new terminal. A smaller pump establishes controlled water pressure of 25 bar throughout the whole system. In the event that one of the sprinklers for water mist should open due to increased temperature, the pressure in the installation falls, which triggers the main pump that provides a dynamic pressure of 140 bar at the pump.

The whole system is divided into 6 branches, separated by normally opened zone valves. When the extinguishing is finished, the zone valve is closed manually, until normal state is restored and the triggered sprinklers are replaced.

The main pipelines are stainless pipes with the outer diameter of 38 mm, the pipelines to the sprinklers are stainless pipes with the outer diameter of 12 mm.

In most rooms, rapidly performing sprinklers HI-FOG 2000 C2 are installed which may cover up to 25 m2 of surface area with an RTI index of 25 and the release temperature of 57 °C.

Zarja Elektronika and its partner Marioff carried out the installation works professionally, within the deadline and in constant cooperation with the project designer, the investor, and the supervisor. The professionalism of the investor should be emphasized – they were aware of the need for effective and active fire protection, which at the same time allows the shortest possible time to restore normal operation of the terminal after a potential fire and ensures the safety of both people and equipment.

The HI-FOG water mist extinguishing system was the first system of its kind in Slovenia, which is why it was necessary to put slightly more effort into proving the conformity of the project and the implementation with regulations and standards. The final approval was given by the commission of the VdS, a subsidiary of the German Insurance Association, which verified the entire system and its performance on two visits to the facility, and issued a certificate of conformity.

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