• 20 January 2023
  • Author: © Fire-TechInfo I Marketing article

Low pressure water mist – the modern approach in firefighting industry, Part 1

 

For the last thirty years, water mist fire protection has evolved from a theory to an increasingly widely accepted alternative to traditional water, foam or gas fire protection systems. Water mist offers better protection efficiency, significantly less water consumption and lower investment costs.

Water mist systems are a special category of fire protection systems that, depending on the class of fire hazard, can be designed to control, suppress or extinguish a fire. Their effectiveness is proven by full-scale tests for each class of fire hazard.

 

Fire test. Source: © VID FIREKILL
Fire test. Source: © VID FIREKILL

There are two main types of water mist systems – those that operate at low pressure (up to 16 bar) and others that operate at high pressure (from 50 to 140 bar). Both types of systems use a very fine water spray composed of micro-sized water droplets. Until recently, it was thought that droplet size and extinguishing efficiency were closely related, and that the smaller the droplets are, the more efficient the system is. And the smaller droplet size was automatically associated with the operation of high-pressure systems, giving them priority over the low-pressure water mist systems.

The modern approach to the development of water mist technology reveals many different factors on which the effectiveness of water mist systems depends. These factors may be, on the one hand, the water mist spray characteristics such as distribution of droplet size; flux density, expressed as the amount of water released per unit volume / area per minute; spray dynamics, expressed in the speed and trajectory of the droplets. On the other hand, it is necessary to take into account the specific fire scenario (geometry of the room, type and size of flammable materials, ventilation conditions, ambient temperature, etc.). Factors such as enclosure effect, dynamic mixing created by the discharge by a group of nozzles, also affect the performance of water mist systems.

Low-pressure water mist. Source: © VID FIREKILL
Low-pressure water mist. Source: © VID FIREKILL

Due to this complexity of the fire extinguishing process, the relationship between the fire scenario and the characteristic of the system is not unambiguous, but very complex. Neither the droplets size nor the operating pressure determines the effectiveness of the system. Only full-scale fire tests prove whether a system can handle a certain risk. Moreover, empirical studies show that water mist with a combined distribution of different sized droplets achieves higher efficiency compared to water mist composed of the same or even very small droplet size. For this reason, water mist systems are always selected on the basis of positive fire test results.

The modern research with a combination of experimental and computational methods, the compilation of computer models and their validation by fire tests allow much more efficient and effective development of water mist systems. This approach was followed by VID Fire-Kill ApS when developing and creating the FFIREKILL™ system

Low-pressure water mist nozzles. Source: © VID FIREKILL
Low-pressure water mist nozzles. Source: © VID FIREKILL

 

Why is the FIREKILL™ system so efficient??

The FIREKILL™ low pressure water mist system is a complete solution for protection against many fire hazards in modern buildings and industrial facilities. The system includes a full range of equipment (nozzles, pumps, valves, etc.), documents and applicability according to CEN EN 14972, system manual for design, installation, operation and maintenance, certificates and approvals according to many standards, including third parties, as well as protocols of full-scale fire tests.

Compared to gas agents and traditional sprinkler systems, the low pressure water mist technology implemented in the FIREKILLТМ system shows a number of advantages, summarized in the following most important characteristics:

  • Completely safe for people
  • Completely harmless to the environment
  • Low investment price
  • No damage or minimized damage of the extinguishing agent – water
  • High efficiency for almost all fire classes, including special fire hazards

The extinguishing efficiency can be explained by two chemical reactions that occur during combustion. The first chemical reaction (pyrolysis) takes place on the surface of combustible material, when under the influence of heat the combustible material begins to decompose and release flammable gases. The second chemical reaction (oxidation) takes place in the atmosphere above the surface of flammable material, when under the influence of heat energy, the oxygen molecules decompose and bind to the molecules of flammable gases. This process releases extra energy and thus maintains the combustion process.

Water mist affects both processes through several extinguishing mechanisms – primary and secondary:

Primary mechanisms:

1. Heat extraction:

  • Cooling of fire plume
  • Cooling/ Wetting of the fuel surface

2. Displacement of oxygen and other combustion gases:

  • Displacement of oxygen.
  • Dilution of combustion gases/ fuel vapor.

Secondary mechanisms:

3. Heat transfer attenuation.

4. Kinetic effects.

Through specially designed nozzles, the system distributes water mist droplets at a certain speed and with a wide range of sizes, ranging from invisible to large droplets. The wide variety of droplets help to fight fire in many different ways at once. For example, the large droplets penetrate the flames and fall on the surface of the combustible material where they prevent flammable gases from being formatted. The medium sized droplets penetrate the fire, evaporate and create an inert environment, just where it is needed, in the heart of the fire. The small size droplets evaporate at the immediate vicinity of the fire, cool the atmosphere and block the fire spreading to the surrounding objects.

Thus, using four methods to eliminate the fire and its consequences, the system optimizes water use and the result is maximum efficiency.

Continued in Part 2

Contact details:

TechInfo
Partner for Bulgaria of
VID FIREKILL

20 Frederic Joliot-Curie, 1113 Sofia
Моbile: +359 888 441 336
E-mail: info@techinfo.bg
Website: www.techinfo.bg

 

Source: © TechInfo, © VID FIREKILL
Photos: © VID FIREKILL

Special publications

Water mist fire extinguishing systems – sustainable technology in the fire protection industry
  The use of water mist systems as a modern sustainable technology in the firefighting industry has grown significantly over the last two decades. Water...
Low pressure water mist – the modern approach in firefighting industry
For the last thirty years, water mist fire protection has evolved from a theory to an increasingly widely accepted alternative to traditional water, foam or...

Norms and standards

Standards: EN 14972-1:2020
Abstract/Scope This document specifies requirements and gives recommendations for the design, installation, inspection and maintenance of all types of fixed land based water mist systems....
Standards: EN 54-1:2021
  Abstract/Scope: This document defines the terms and definitions that are used throughout the EN 54 series of standards. It gives the principles on which...
Standards: EN 16750:2017+A1:2020
Abstract/Scope: This European standard specifies oxygen reduction systems that are used as fire prevention systems by creating an atmosphere in an area which is having...