MicroDrop High Pressure Water Mist

The Tyco MicroDrop® high pressure water mist system works at a pressure of typically 100bar to deliver water as a fine atomised mist. This mist is quickly converted into steam that smothers the fire and prevents further oxygen from reaching it. At the same time, the evaporation creates a significant cooling effect. In this way, water mist combines the fire suppression properties of both conventional water-based deluge or sprinkler systems and gaseous systems.

Water has excellent heat absorption properties absorbing 4.18 kjoules / kg. / ºC and 2260 kjoules / kg. to convert to steam, plus a 1630:1 expansion in doing so. In order to exploit these properties, the surface area of the water droplets must be optimised and their transit time (before hitting surfaces) maximised. In doing so, fire suppression of surface flaming fires can be achieved by a combination of:

• Heat extraction from the fire and fuel
• Oxygen reduction by steam smothering at the flame front
• Blocking of radiant heat transfer
• Cooling of combustion gases

In order to be effective, the droplets must reach and be entrained in the combustion airflow. With MicroDrop® high pressure water mist systems, this is successfully achieved with additional velocity to penetrate the fire.

Water Mist is defined in NFPA 750 as a water spray for which the Dv0.99, for the flow-weighted cumulative volumetric distribution of water droplets, is less than 1000 microns at the minimum design operating pressure of the water mist nozzle.

The average droplet size of a Tyco MicroDrop® high pressure water mist system ‘mist’ yield a total surface area at least 100 times greater than conventional sprinkler droplets for the same volume of water. Therefore, much smaller amounts of water are required to absorb the equivalent amount of energy from the fire. Inerting (oxygen depletion) at the flame front can also take place locally or in the whole enclosed space, particularly where the fire is large in relation to the space. Wetting of surfaces is also an important effect where control of deep seated fires is required. A further highly beneficial effect is the dramatic reduction of harmful products of combustion caused by washing out of smoke particles from the fire.