Low pressure water mist extinguishing system

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Low-pressure water mist extinguishing systems are extinguishing and fire-fighting systems which, due to their nozzle design, enable a fire to be fought efficiently with little water in the low-pressure range .

Fire fighting system / fire extinguishing system

A fire extinguishing system is a permanently operational technical system that extinguishes a fire with an extinguishing agent . Stationary (stationary) fire extinguishing systems often consist of a pipeline system with suitable output devices (examples: sprinklers, extinguishing nozzles) through which the extinguishing agent is discharged in the event of an emergency. They are triggered either indirectly by fire alarm and extinguishing control systems or directly by mechanical fire detection and triggering elements (examples: glass barrel, fusible link) automatically or manually. The systems should automatically extinguish a fire or control it until the fire brigade arrives to extinguish it.

Mobile fire extinguishing systems are permanently installed in fire fighting vehicles, as swap trailers or as containers for fire fighting vehicles, which, depending on the application, come to the location on the carrier vehicle. One example is a mobile carbon dioxide fire extinguishing system for companies in the chemical industry.

Types of fire extinguishing systems

  • Sprinkler systems
  • Wet sprinkler system
  • Sprinkler drying systems
  • Pilot operated sprinkler systems
  • Water spray extinguishing systems
  • Water mist extinguishing systems
  • High pressure water mist extinguishing systems
  • Low pressure water mist extinguishing systems
  • Foam extinguishing systems
  • Spark extinguishing systems
  • Carbon dioxide extinguishing system (CO 2 extinguishing system)
  • Inert gas extinguishing systems
  • Inert gas extinguishing systems with gas mixtures (Inergen, Argonite)
  • Chemical extinguishing systems (Halon, FM-200, Novec 1230)
  • Powder extinguishing systems and extinguishing aerosols

Water mist extinguishing systems

In a water mist extinguishing system, very small drops of water are used as an extinguishing agent. The average size of a water drop is around 10 to 100 μm (comparison of fine spray extinguishing systems: 250 to 500 μm). Since the extinguishing nozzles spray very fine water droplets, the surface area of ​​the amount of water introduced can be increased many times over. In this way, energy is withdrawn from the fire faster and the cooling effect of the extinguishing agent water can be optimized. In addition, the amount of extinguishing water and thus the water supply as well as damage caused by the water extinguishing agent can be reduced.

history

Low pressure water mist was first patented in the 1930s. An example is patent specification no. 512544 liquid atomizer. At that time, the physical properties of fire and water were already known, so that water mist technology was researched in detail and its efficiency was proven, especially in the military sector. The functions at that time were mostly based on the production of fog at high pressure. Since high pressures were and are rather difficult to achieve, a focus was placed on the low pressure range. In the former countries of the Eastern Bloc, research was increasingly focused on the low-pressure water mist technology. There, in the course of the Cold War, there were developments in low-pressure water mist extinguishing systems for tanks and other systems that were very far ahead of their time. In the former countries of the Eastern Bloc, low pressure water mist was used because of its positive efficiency compared to the economic costs. In the 1970s a standard was developed on the subject of water mist extinguishing systems, the TGL 32457. The NFPA 750 Standard on Water Mist Fire Protection Systems has existed since 2010 .

construction

In principle, a low-pressure water mist extinguishing system is constructed similarly to a conventional extinguishing system. It consists of thermally triggered nozzles, 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 low-pressure water mist extinguishing system requires significantly less water than a conventional sprinkler system, and the dimensions of the individual components are therefore much smaller.

species

As with conventional fire-fighting systems, there are also various options for implementing the system with low-pressure water mist extinguishing systems. They can be designed and manufactured both wet and dry or as a pilot-operated system. It is important here that the specified protection goal is always achieved.

How a low pressure water mist extinguishing system works

The low-pressure water mist extinguishing system achieves the same efficiency with less water. This is possible due to the nozzles specially manufactured for this purpose. These nozzles enable drop sizes of 10 to 100 µm to be produced. It is important here that this can already be done in the low pressure range (according to DIN 14972 <12.5 bar), because this is the only way to speak of low pressure water mist.

With the low-pressure water mist technology, the smaller droplet size, compared to the sprinkler system, results in an enlarged reaction surface of the extinguishing water introduced. This enlargement of the surface causes a faster evaporation of the extinguishing water and thus a highly effective cooling of the atmosphere. In addition to this cooling, there is an inerting effect at the source of the fire.

The characteristic variable for the speed of vapor development from a liquid is the evaporation coefficient K [cm / sec * mmHg]. This evaporation coefficient clarifies 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 is absorbed in one second per liter of water times Kelvin, depending on the droplet diameter, clearly shows that small droplets 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

In direct comparison to sprinkler systems , low pressure 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 that have been built up to now, it can be assumed that the extinguishing water supply and consumption will be up to 80% lower. There is a direct connection between the lower expenditure on retention of extinguishing water, since less contaminated extinguishing water is produced. These factors also allow the installations to be carried out more cheaply. You can also install low-pressure water mist extinguishing systems in concrete.

Areas of application

  • Hotels
  • Hospitals
  • Meeting places
  • Event venues
  • 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 warehouse / warehouses / storage rooms
  • Manufacturing halls in industry
  • Water curtain systems
  • Cable routes / conveyor belts

See also

literature

  • Schremmer, U. (1997) Stationary automatic water misting systems. Fire protection 38 (5), pp. 20–25
  • Schreiber Porst, extinguishing agent, State Publishing House of the GDR 1972

Web links