Water mist extinguishing efficiency
Extinguishing efficiency. Firefighters determine the extinguishing efficiency with fog systems to be 10 times greater than traditional sprinkler systems. Systems based on HP pressure pumps are characterized by many times higher operating pressure. Thus, much higher extinguishing efficiency compared to older solutions, where the source of pressure is a cylinder with carbon dioxide.
Fast heat transfer with the environment
From the small diameter of droplets in the water mist, can get a large specific surface area of sprayed water. Assuming a droplet diameter of 10 μm, we obtain as much as 600 m2 from one liter of water. This allows for very fast heat transfer with the environment. Evaporating water has a high specific heat of 2500 kJ /kg. It is a relatively low (for fire conditions) boiling point – 100°C.
Extinguishing triangle
We know from the fire triangle that in order for a fire to occur, the following conditions must be met:
- sufficiently high temperature,
- sufficiently high oxygen concentration,
- combustible material.
Extinguishing with water mist hits 2 components at the same time. Evaporating water takes a huge amount of heat from the fire environment, lowering its temperature. It can be assumed that the evaporation of water consumes an average of 8 times more heat flux than heating water from 20 °C to 100 °C. The conclusion is that in order to achieve the best cooling efficiency, water should be given in such a way that the largest number of water droplets undergoes a phase transformation. This way is to give it in the form of extinguishing water mist TISSA.
In addition, evaporated water increases its volume more than 1700 times. The condition for this is the earlier evaporation of water, because it is the water vapor (and not water drops) that displaces oxygen from the combustion zone. That is why it is so important that the water is given in the form of an extinguishing water mist, in such a way that it can evaporate as soon as possible. Most common materials go out if the oxygen concentration drops below 13-16%.
