The main advantages of water mist fire suppression systems are:
- Environmentally friendly – will not damage the environment.
- Safe for personnel in occupied areas.
- Fast action – no need for time delays.
- Causes minimal damage to surroundings.
- Easy to retrofit.
- Economical.
- Minimum cost to refill system.
- Very small amounts of water used to achieve suppression and control.
- Easy to refill.
- Rapid fire suppresion and control.
- Neat and economical installations with small diameter pipes.
- Suitable for local application and total flood hazards.
- Does not create by-products of combustion.
- Low maintenance costs.
Codes of Practice
The Design of water mist systems will be based on the requirements of NFPA750 and draft European standard CEN14972. All third party equipment, cylinders, nozzles, pumps etc carry the highest standards of approval and will be supported by testing data for each system.
How Water Mist Systems Work
Cooling
Water spray in droplets of micron size produces a large surface area for heat absorption. Once in contact with hot bodies and gases, these droplets convert to vapour absorbing a large quantity of heat, equivalent to 540 calories per gram.
Smothering
The water in its vapour state occupies 1,600 times more volume than as a liquid and displaces an equivalent volume of oxygen, thus creating a smothering effect. If both the water vapour generated and the temperature in the hazard is high enough, the concentration of oxygen can fall drastically in the whole room.
Attenuation
The water mist cloud generated will attenuate radiation to limit the propagation of fire to other areas while at the same time diminishing the overall heat radiation throughout the room.
Typical Water Mist Applications
Water mist is used in very different situations. It is designed according to two different functions (according to each hazard) fire control or fire suppression.
Fire Control (Total Flooding)
Limiting the growth and the spread of fire, cooling the adjoining fuel and containing upper gas temperatures.
Typical applications would be:
- Computer rooms
- Occupied rooms and class A fires
- Archives
- Cable trays
- Telecommunication centres
- Spill of flammable liquids
Fire Suppression (Local Application)
Complete fire suppression of the risk.
Typical applications would be:
- Commercial kitchens and food industry
- Warehouses containing flammable liquids
- Turbine and transformer rooms
- Engine test cells
- Diesel engines and alternators
- Paint spray booths
- Mechanical escalators (excluding the electrical-type risks in the drive rooms)
Water Mist Discharge Nozzles
There are several different models of nozzles suitable for the hazard to be protected. The nozzle head is manufactured from stainless steel with housing for a maximum of 5 micro nozzles. A compression fitting is provided for direct connection to the stainless pipe network. OPEN NOZZLE discharges directly once the system is activated.
OPEN NOZZLE
Open nozzle discharges directly once the system is activated.
Water Mist Fire Supression SystemsWater Mist Fire Supression Systems
These nozzles are the most suitable for application in total flooding systems. The nozzles can be fitted with up to five micro-nozzles depending on the design giving flexibility of a wide range of flows. The connecting adaptor is stainless steel compression for easy connection to the stainless supply pipe work.
The nozzle body is formed in two sections to make maintenance operations easier. The micronozzles spray the water correctly with a working pressure of between 80 and 200 bars.
CLOSED NOZZLE
AUTOMATIC NOZZLE HEADS
A mixture of the above-mentioned nozzle heads. When connected to a wet pipe system, they allow the detection of the fire by means of a bulb (same RTI) allowing activation of the remaining nozzles when the pressure in the pipe exceeds a minimum value (60 bar). In this way, it is possible to design total flooding systems with detection included.
As with the closed head, it can be equipped with up to four micro-nozzles depending on the application.
"T" NOZZLE HEADS TO PIPE
This is the most economical head from the whole range. It allows the connection of a unique micro nozzle reducing the cost. This head is assembled directly onto a T or elbow by means of a nozzle joint with a Ø 12 or 15 mm compression nut included in price. This is the most suitable nozzle for applications in kitchens, escalators and false floors/ceilings.
All nozzle heads have a FB85 filter to avoid possible blockage of the micro nozzles from particulate contaminant.
Water Mist System Categories
Water mist systems can be split into two categories as follows:
High Pressure Water Mist
High pressure water mist systems (HPWM) consist of high pressure pumps and storage tanks or cylinders of water and pressurised nitrogen cylinders to discharge the water. The installation is carried out utilising small bore stainless steel pipe work and high pressure discharge nozzles. This system uses minimal quantities of water in comparison to low pressure systems.
Low Pressure Water Mist
Low pressure water mist systems (LPWM) consist of pumps and storage tanks, they generally use more water than HPWM systems although significantly less than traditional sprinkler systems. Due to the lower pressures involved the pipe work installation can be carried out using a variety of different materials such as copper pipe and even specialist plastic pipe work.