075: Water mist extinguishing system

Water mist system are using tiny droplets or in other words microscopic (dry) particles of water to control or extinguish the fires. When these fine drops reach the flame and hot air, evaporate and turn to the steam. This conversion (water drop to steam) means absorbing the heat and reducing the temperature. The movement of steam also displaces the oxygen in the area. So in short:

• Remove the heat and temperature control
• Displacing and reducing the oxygen with steam

Note1: Diameter of droplet must be less than 1 mm (Approximately one-fifth of the size of drops in a sprinkler system).

Note2: Typically used for fire classes of A (combustible materials) and E (electrical fire).

Application: Hospitals, valuable books / documents, clean room, telecommunication facilities, household and professional kitchen, food factory, food preparation area

Spray characteristics:

• Droplet size
• Flux density
• Spray dynamics

Required paramters for design:

• Fire size
• Shielding of the fuel
• Ventilation conditions

Water mist system types:

• Fixed system (NFPA750)

• Local application systems: specific object or hazard
• Occupancy protection systems: building or a part of a building
• Total compartment application systems
• Zoned application systems

• Portable extinguisher

Water mist system types - based on pressure (NFPA 750):

• Low pressure (up to 175 PSI)
• Intermediate pressure (175 to 500 PSI)
• High pressure (more than 500 PSI)

Water mist system types - based on source:

1- Single fluid (normal water, de-ionized / de-mineralised water)

2- Twin fluid (water-air, water-nitrogen)

Note3: De-ionized water doesn't conduct electricity.

Water mist components:

1. Nozzle (Hand extinguisher: Supersonic)
2. Sprinkler head
3. Pipe and hangers
4. Fittings and connections
5. Valve (testing and draining)

Advantage:

• Extinguishing the various fire classes
• Reduces dispersion of burning materials
• Leaving no residue
• No harmful substances (no risk of inhalation, skin injuries, eye burning etc.)
• Eco-friendly

Note4: Installation of water mist system must be according to standards and manufacturer regulations.