Water mist extinguishing system

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From a building law perspective, water mist extinguishing systems are mostly automatic extinguishing systems which, due to their nozzle design, eject the extinguishing water as very small drops with a diameter of approx. 10 to 1000 µm in order to efficiently fight a fire with little water. They serve to control incipient fires and enable effective extinguishing work. Generally defined, water mist extinguishing systems are mostly automatic systems for fire fighting , for extinguishing fires, for keeping smoke free or for component cooling . Even for hygienic cleaning z. B. by slaughterhouses water mist systems are used. The term water mist extinguishing system is then no longer applicable.

Definitions or terms of water extinguishing system technology

"Extinguishing system" or fire fighting or fire extinguishing system

An "extinguishing system" is a technical system that is always ready for operation and that uses an extinguishing agent to contain a fire . Stationary (stationary) "extinguishing systems" often consist of a pipeline system with suitable extinguishing water ejection devices, e.g. B. sprinkler heads or extinguishing nozzles that deliver the extinguishing agent when needed. You are either indirectly through fire alarm systems or directly through fire detection and triggering elements such. B. glass vials or fusible link triggered. The systems should control a fire automatically until the fire brigade arrives to extinguish it. Therefore the colloquial term “extinguishing system” is rather misleading and is therefore often replaced in the literature with the terms fire fighting or fire extinguishing system. Mobile systems are available as swap trailers or as containers for fire fighting vehicles, which, depending on the application, come to the location on the carrier vehicle. Examples of this are mobile carbon dioxide, powder and water mist extinguishing systems.

Terms for stationary water extinguishing systems and their regulations

(Other systems, e.g. with foam as an extinguishing agent, are not considered here.) In order to find out the conceptual and thus also the technical differences and subtleties, one or more deep looks into the harmonized DIN EN standards are required .

There are three main categories or types of systems:

  • A - the "sprinkler system", currently regulated by DIN EN 12845
  • B - the "fine spray extinguishing system", currently regulated by DIN EN 14972 and
  • C - the water spray extinguishing system , currently regulated by DIN CEN / TS 14816

Both open and closed (automatic) sprinkler heads or (spray) nozzles can be used in all three system types. In particular, no further distinction is made in the respective standards for “sprinkler system” (A) and “water spray extinguishing system” (C). In the case of the “fine spray extinguishing system” (B), the DIN EN standard distinguishes between “fine spray extinguishing system with open nozzles” (B.1) and “fine spray extinguishing system with automatic nozzles” (B.2), with the second being the term “fine spray sprinkler system” is also used.

In particular, the water mist extinguishing system is actually not clearly anchored in the standards and there is no further subdivision of types of water extinguishing systems. A different derivation is therefore required.

Since insurance companies often also have requirements for water extinguishing systems in construction projects , the guidelines of VdS Schadenverhütung GmbH are recognized rules of technology for them and for many planners and specialist planners. Based on the VdS guidelines, three types of water extinguishing systems can initially be identified:

  • D - the "sprinkler system", current guideline VdS CEA 4001
  • E - the "water mist extinguishing system" and "water mist sprinkler system", current guideline VdS 3188 (here: high pressure systems)
  • F - the "water spray extinguishing system", current guideline VdS 2109

In terms of the system, at least two of the three system types can be equated with two types of the DIN standards: A ≙ D and C ≙ F C and E cannot, however, be equated without further ado, since VdS 3188 is only used for high-pressure systems. The low-pressure systems of "water mist extinguishing systems" or "water mist sprinkler systems", on the other hand, are in turn recorded in VdS 2109 and VdS CEA 4001. In VdS 3188, however, an umbrella term for “water mist extinguishing system” and “water mist sprinkler system” can be found, which summarizes and is better suited for comparing it with “fine spray extinguishing systems” (B): “water mist systems” (new for E )

"Water mist systems" can therefore now be subdivided as follows:

  • E.1 - in the low pressure range and with automatic nozzles they are technically regulated in VdS CEA 4001; In common parlance called "low pressure water mist sprinkler system".
  • E.2 - in the high pressure area and with automatic nozzles they are technically regulated in VdS 3188; Called in parlance the "high pressure water mist sprinkler system".
  • E.3 - in the low pressure range and with open nozzles they are technically regulated in VdS 2109; In common parlance called "low pressure water mist extinguishing system".
  • E.4 - in the high pressure area and with open nozzles they are technically regulated in VdS 3188; In common parlance called "high pressure water mist extinguishing system".

In summary, it can be stated that the term “water mist extinguishing system” originates from the VdS guidelines on water mist systems, but there are comparable systems as “fine spray extinguishing systems” according to DIN EN.

The differences between the water mist system types are essentially the use of automatic (closed) nozzles (water mist sprinkler system) or open nozzles (water mist extinguishing system) and the pressure with which the water is pumped through the system. Systems with automatic nozzles or sprinklers react to temperatures, the pipe network is usually permanently filled with water. Systems with open nozzles or sprinklers, on the other hand, are controlled by a fire alarm system because the pipe network is always dry here. Both DIN EN 14972 ("Fine spray extinguishing system", see B) and VdS 3188 make statements on pressure: ≤16 bar (low pressure) and> 16 bar (high pressure).

Standards for water mist extinguishing systems

German standards and guidelines

  • DIN EN 14972 - Fixed fire fighting systems - Fine spray extinguishing systems - Planning, installation, inspection and maintenance.
  • DIN CEN / TS 14816 - Fixed fire fighting systems - Water spray extinguishing systems - Planning, installation and maintenance
  • VdS 3188 (Schadenverhütung GmbH) - water mist sprinkler systems and water mist extinguishing systems (high pressure systems)
  • VdS 2109 (Schadenverhütung GmbH) - water spray extinguishing systems - planning and installation

German standards and guidelines related to WN-LA

  • DIN EN 12845 - Fixed fire fighting systems - Automatic sprinkler systems - Planning, installation and maintenance
  • VdS 2496 (Schadenverhütung GmbH) - control of fire extinguishing systems - planning and installation
  • VdS CEA 4001 (Schadenverhütung GmbH) guideline for sprinkler systems - planning and installation
  • VdS 2212 (Schadenverhütung GmbH) - operating log for water extinguishing systems

International standards and guidelines for WN-LA

  • FM Global (Factory Mutual) 5560 - American National Standard for Water Mist Systems
  • FM Global (Factory Mutual) Data Sheet 4-2 - WATER MIST SYSTEMS
  • NFPA (national fire protection association) 750 - Standard on Water Mist Fire Protection Systems.
  • IMO (international maritime organization) SOLAS 1974 - Chapter II – 2 - Construction - Fire protection, fire detection and fire extinction.
  • IMO (international maritime organization) MSC 1165 - Revised Guidelines for the approval of equivalent water-based-fire-extinguishing systems for machinery spaces and cargo pump-rooms.
  • IMO (international maritime organization) A.800 - Revised Guidelines for the approval of sprinkler systems equivalent tot hat referred to in SOLAS regulation II-2/12.
  • British Standard BS 8489-1: 2016 - BS 8489-1: 2016 - Fixed fire protection systems. Industrial and commercial watermist systems. Code of Practice for Design and Installation.

History of water mist extinguishing systems

Water mist was first patented in the 1930s. On June 26, 1928, Benigne Pierre Marie Le Gouz de Saint Seine applied for his patent in Paris to “extinguish chimney fires” by injecting a water mist below the scene of the fire. In his patent he describes impressively how the water droplets, in contrast to water droplets from a shower (sprinkler), are carried away by the draft of air rising in the chimney shaft. In this way, the water droplets reach the site of the fire, where they largely evaporate and the fire is suffocated (inerting effect at the source of the fire). Conceivable water additives and the possibilities at that time to generate pressure in the water storage tank are also listed. For this purpose, compressed gas, carbon dioxide or compressed air generated with a mechanical pump should be used (just like today). It seems to be the oldest patent for water mist extinguishing technology.

The central scientific institute for fire fighting of the former USSR investigated the suitability of water mist extinguishing systems in the 1950s and in 1961 the Czechoslovak Fire Protection Association published a brochure on experiments with new water mist extinguishing devices. In these tests, the extinguishing effect of mist on liquid fires was also investigated. In the process, round steel tubs with a diameter of three meters were filled with flammable liquids such as oil , gasoline , other highly flammable and explosive liquids, ignited and extinguished with water mist. The tests of the then np THZ (Czechoslovak state company for industrial extinguishing systems) confirmed that fog can be very effective in extinguishing liquid fires.

In the 1980s, np Karosa (successor to np THZ) developed stationary water mist extinguishing systems for cable ducts. The effectiveness and efficiency of the water mist extinguishing systems (from now on only WNLA) was also successfully proven in a fire test. Messrs. Total Walther from Cologne took advantage of the lessons learned in developing their own WNLA later. The first patent application was filed on December 16, 1994 and published on September 13, 1995. From the mid-90s of the last century, numerous other patents for WNLA and its components followed.

In the maritime sector, water mist extinguishing systems were spread across Europe a little earlier. This first happened at sea in the 1980s, because when extinguishing with fog you need significantly less extinguishing water, which has to be carried on ships. Due to its advantages in certain applications, from around the turn of the millennium the spread of the mist extinguishing technology also took place on land. The bans on halons were also important for the spread of WNLA , as water mist, which is clean and ecologically harmless, proved to be a suitable substitute.

Construction of water mist extinguishing systems

In principle, a water mist extinguishing system is constructed in a similar way to a sprinkler system. It has devices for fire detection (with open systems also a fire alarm system), water ejection devices, a pipeline network , an alarm valve station, a pump and an extinguishing water reservoir. As with other systems, only approved and tested components are used here, so that a failure of the system can be reduced to a minimum. The most significant difference is that a water mist extinguishing system requires significantly less water than a conventional sprinkler system, and the dimensions of the individual components are therefore smaller. This requires careful filtration of the extinguishing water so that the fine water mist nozzles do not clog.

How water mist extinguishing systems work

A water mist extinguishing system can achieve the same or better extinguishing effect than a conventional sprinkler system in certain applications with less water. This is possible due to the nozzles specially manufactured for this purpose and the usually higher operating pressure of the system. The nozzles make it possible to produce drop sizes from 10 to 1000 µm. (Natural droplets such as raindrops have a diameter of 3000 to at least 1000 µm.) With water mist technology, the reduced size of the droplets compared to the sprinkler system (droplet size between 1500 and 500 µm) leads to an enlarged reaction surface of the extinguishing water introduced . In this way, energy is withdrawn from the fire faster and the cooling effect of the extinguishing water is optimized. In addition, mist can evaporate faster due to the size of the water droplets. In doing so, it can displace oxygen by increasing its volume by around 1700 times. In addition to better cooling, there is also an inerting effect at the source of the fire. Extinguishing is further facilitated by the fact that the mist can float depending on the size of the droplets and is thus sucked into the fire with the air flowing in due to the thermal dynamics of the fire. Normally large water droplets, on the other hand, can "only" fall onto the flame. The characteristic variable for the speed of vapor development from a liquid is the evaporation coefficient K [cm / sec * mmHg]. This evaporation coefficient illustrates the role of the surface properties of the water: the more surface can react, the faster the water evaporates and the more energy is consumed in the same time unit. The heat flow , which, depending on the droplet diameter , is absorbed in one second per liter of water times Kelvin , clearly shows that small drops can absorb more energy. As a guideline, various literature sources show that a droplet diameter of d = 100 µm can absorb approximately 12 W / (l * K), whereas a droplet diameter of d = 500 µm can only absorb about 1 W / (l * K).

Advantages of water mist extinguishing systems

In direct comparison to sprinkler systems, water mist extinguishing systems have several obvious advantages. Probably the most obvious is the lower consumption of extinguishing water. This is accompanied by a significantly lower supply of extinguishing water, which, as a side effect, can mean more usable space for the user. Due to the systems built up to now, it is possible to speak of up to 80% less extinguishing water supply and lower consumption. There is a direct connection between the lower expenditure on retention of extinguishing water, since less contaminated extinguishing water is produced. The extinguishing damage to the building is also reduced. The smaller amount of water also makes it possible to make the system parts smaller and thus also to simplify assembly. The stainless steel that is always used in high-pressure systems for pipes, screw connections and mostly also for the storage container is very durable and reduces maintenance costs. Adapting or adding to the pipe systems of water mist extinguishing systems in existing buildings is usually cheaper because smaller pipes can be laid in the building. Compared to extinguishing systems that use halons for extinguishing (now prohibited), water is clean and ecologically harmless.

Disadvantages of water mist extinguishing systems

In direct comparison to sprinkler systems, water mist extinguishing systems have several disadvantages. Due to the high pressure in high pressure systems, the thin pipes and fittings are made of stainless steel. The nozzles and heads are small technological marvels in both low-pressure and high-pressure systems and are therefore usually expensive to purchase and replace. Compared to sprinklers, it is necessary to ensure that the extinguishing water is kept clean, which is why extinguishing water filtration is always required in order not to clog the pipes or the nozzles. The storage containers are also mostly made of stainless steel or at least plastic because they are required to be kept clean. Another "disadvantage" compared to sprinkler systems is the exact dimensioning and planning of the systems, which is always required, since the water mist can only be more efficient if the droplet size and the flow rate or the K value of the nozzles (heads) exactly match the fire load is designed. That takes experts.

Areas of application for water mist extinguishing systems

Hotels, hospitals, meeting places, event locations, underground garages / multi-storey car parks, office buildings / administration buildings, churches / museums / archives / listed buildings and areas, power plants / turbines / generators / internal transformers / cable ducts and shafts, high-bay warehouses / warehouses / storage rooms, production halls in the Industry, water curtain systems, cable routes / conveyor belts

literature

  • Macák V .: "Hašení vodní mlhou" Knižnice požární ochrany , Volume 2, Prague 1961
  • Schreiber Porst: Löschmittel , State Publishing House of the GDR 1972
  • Schremmer U .: Stationary automatic water misting systems - principles, mode of operation, design and application limits. Dissertation, Zeitz / Elster 1996
  • Kunkelmann J .: Fire protection research of the federal states of the Federal Republic of Germany, reports on water mist extinguishing systems. Karlsruhe 2007
  • May Lakkonen: History of modern water mist fire protection. In: international water mist association (November 2008)
  • Rybář P .: Mlhová stabilní hasicí zařízení pro protipožární ochranu objektů a technologií. 2017
  • Kopp R .: Modern Firefighting with Water Mist. Verlag Moderne Industrie, Munich 2017

Web links

Individual evidence