Why is water mist so effective in fighting fires? When extinguishing a fire, water mist produces a higher rate of heat extraction and at the same time uses less water.
The efficiency of water mist in fighting fires has been known in expert circles for years. Until now, the water mist was applied by means of nozzle technology, which, however, for technical reasons limited the throwing range to only a few meters. This, of course, also limited the range of possible applications. We at EmiControls have solved this problem: thanks to the use of a propeller turbine, the water mist can now be applied over a long distance.
One advantage of water mist over conventional water jets is, that it envelops objects and therefore cools and extinguishes them very efficiently. Here’s how it works: The turbine atomizes the water into a fine mist. Compared to conventional monitors, fire extinguishing turbines produce smaller droplets that are sprayed using propellers. The advantage of these smaller droplets is that they create a larger water surface area and thus a larger heat absorption surface. The fine mist also has a lower sedimentation rate and can easily envelop burning objects. In this way, it often reaches hidden fire sources that are inaccessible to the conventional extinguishing jet.
Conclusion: The characteristics of water mist allow efficient firefighting with minimal use of water: more heat is extracted from the source of the fire, the cooling effect has a positive effect on the direct ambient temperature, smoke and soot particles are bound and knocked down more quickly by the water mist.
The water mist turbine combines all the previously mentioned advantages of water mist with the power of a turbine: it thus represents a new and innovative generation of firefighting. Its unique selling point: the water mist turbine is capable of atomizing large quantities of water and distributing it over a large area, yet with pinpoint accuracy – and all this at low water pressure. Other advantages of the water mist turbine are:
An optimal cooling effect can be achieved either by forming a barrier, through direct application and by an even distribution on the surface of the object being cooled. Water mist is excellent as an extinguishing agent, thanks to the high cooling effect of directly applying the atomized water straight onto the flame.
In practice, the potential range of applications for our firefighting turbines is very extensive. It covers everything from the chemical sector (where firefighting often includes dealing with pollutants) to recycling plants, companies with a high fire load (such as aircraft hangars, tank farms or refineries, industries that work with timber, etc., or high voltage units.
A test trial (carried out in 2011) clearly shows the difference between the water mist turbine and a conventional extinguishing method (see table). Tested on a 160 m² area with 2,400 liters of gasoline set on fire (350MW HHR – 1% AFFF foam), this is the largest documented fire test with water mist in Europe. The test was conducted by MPA Dresden, at the MO refinery training site in Hungary.
From a physical and thermodynamical point of view, there are several mechanisms acting simultaneously, by which water mist extinguishes fire.
1. Cooling effect
Primarily the water mist efficiently cools the fire plume and the fuel surface, extracting a significantly high quantity of heat out of it. This happens thanks to the high latent heat of evaporation (2,442 J/g) of water
2. Inerting effect
The water mist is carried with the air into the source of the fire, where it quickly evaporates due to the high heat. As a result of the enormous increase in the volume of the water droplets as they evaporate (up to 1,700 times), the oxygen at the source of the fire is displaced and the fire is smothered.
3. Absorption of radiant energy
Water mist also absorbs radiant energy as a secondary mechanism and therefore acts as a thermal barrier, preventing surrounding surfaces (or the fuel itself) from being heated by radiation.
Additional positive secondary effects include: gas suppression, burnt gas knock-down, personal protection (as water mist lowers the temperature and eliminates burnt gases faster than any other agent) and cooling of objects
In principle, our firefighting turbines work with water, foam or a mixture of water and foam.
Depending on the spray pattern, the water input can be varied between 100 and 4,700 liters per minute.
