Systems are defined typically by their pressure, so we use NFPA 750. That's a standard for water mist systems, and in that standard, they offer up low pressure systems, intermediate, and high pressure. So low pressure systems operate at around the same pressures that sprinkler systems will operate at. Intermediate pressure is between 175 psi and 500 psi, and then high pressure systems, 500 psi and up. The highest pressure water mist system we made is around 2,300 psi of pressure, so really high pressure system, specialized tubing or piping that's used for that. Now, there are differences between water mist systems and the droplet sizes that they produce, so typically the smaller the water droplet size the better it is at extinguishing a hot fire. Larger droplets can work faster on lower temperature fires, but they all work for the systems that they're approved for or listed for. Reason why we choose 500 psi max to be perfect suitable for all fires and smogs and dust.
Nozzles can be deluge type, so this is a picture of a deluge water mist nozzle open all the time, and so when water flow to it, it will automatically go off, or automatic nozzles. So automatic nozzles would have a little thermal element in them, and when it gets heat to it, just like a sprinkler, it would burst and allow water to flow.
Variance in the water supply sources. Most water mist systems use two things. They use stainless steel pipe, because we don't want it to rust in there. Any rust or particulate in the piping system will get to the nozzles and gum them up, and we don't want that to happen, and then we just use tap water because we don't want the water to become corrosive as it sits there and waits for a fire to happen. AFFF or F500 additive may also be added to the water.
When you look at droplet sizes for water mist systems, one benchmark is that the droplets should be less than 1,000 microns in diameters. So for a system to be considered water mist, it has to have droplets smaller than 1,000 microns, which is the thickness of a dime. Okay? So most sprinkler systems have droplet sizes produced around 5,000 microns, and water mist is less than 1,000. Intermediate pressure water mist systems tend to produce around 300, maybe even 500 micron droplets, and then high pressure systems around 50, maybe to 100, 150 microns in diameter, and so the concept with water mist is we take a given volume of water and break it down into smaller and smaller packets. When we do that, we increase the surface area of that water available to be exposed to the heat of the fire, so it can do some certain things.

The FogFireFighting system is pre-engineered water mist fire suppression system for total compartment protection of houses and machineries. The MicroMist system employs a nozzle which has demonstrated excellent performance extinguishing flammable Class A and liquid (Class B) fire scenarios. Each nozzle flows approximately 2.1 gallons/minute (8 liters/min) of water at 310 psi (21 Bar). A single FogFireFighting system is capable of protecting areas up to 9175 ft3 (260 m3), with a maximum ceiling height of 16’ (4.9m).

The FogFireFighting system is offered in 70 and 112 gallon (267 and 423 liter) configurations. Each system package is skid mounted and includes all necessary valves and actuation components for system operation. System nozzles are ordered separately. Each FogFireFighting package is pre-assembled and tested to ensure system reliability and simplify ease of installation.

Operating Principles
Water is an outstanding fire suppression agent due to its high heat capacity and latent heat of vaporization. The FogFireFighting nozzle uses a plate to slice the small jets of water that flow through the nozzle orifice. The resulting water mist contains a variety of droplet sizes. The larger droplets produced by the nozzle provide the necessary energy and momentum to carry the smaller droplets to the base of the fire where the mist vaporizes and extinguishes the fire. The simple theory behind this development is that a large amount of small droplets have a greater surface area than the same volume of large droplets, therefore absorb more heat.
Water mist systems extinguish fires using the following basic principles:
Cooling - As the mist is converted into vapor it removes heat from the fire source.
Inerting - As the water mist turns to steam it expands approximately 1700 times, forcing oxygen away from the flame front, thus denying it the oxygen necessary to support combustion. (localize inert environment)
Wetting - Primarily for incidental Class A fires; wetting of the surface helps extinguish the fire as well as contain it.

FogFireFighting are designed and have been tested for use in protecting flammable liquids (Class B), ordinary combustible (Class A) materials.

We see water mist growing because it's a safe alternative to total flood carbon dioxide systems. That's one of the main reasons to use it. We see a lot of people they have a choice between water mist and carbon dioxide and water mist system is going to be their choice a many many of times,almost 99%. We even see companies with existing total flood CO2 systems going and tearing them out and getting in water mist because it is safe for people and make smokes dissolving. All the peopledies in fire accident because of smokes and gasses, not because of direct fire. It's a water-efficient alternative to traditional sprinklers. So we can use a water mist system and arrange it in such a way that we could replace the conventional sprinkler system with a water mist sprinkler system, so we see that sometimes happening in buildings, and frankly there's more and more manufacturers developing more applications to be used in the United States market, and so one estimate I heard is that of the systems being installed that could have water mist applied to them, only 5 percent of them are actually using water mist, so a big room for growth for that product category, and we feel that you're going to hear more and more about it over time.

Oxygen displacement effect
The rapid vaporisation of water droplets withdraws energy from the fire. The water vapour, which has a volume 1640 times greater than liquid water, displaces the oxygen directly at the fire source, thereby creating a suffocation effect similar to an extinguishing gas. This only occurs directly at the fire source, meaning there is no danger to people escaping from the fire due to a lack of oxygen. Traditional water based fire fighting systems (e.g. low-pressure water mist systems) use larger droplets, which take considerably longer to vaporise or, in many cases, do not vaporise at all.

Cooling effect
The atomisation of water generates a massive reaction surface area and therefore results into extremely efficient cooling. Energy is withdrawn from the fire rapidly and effectively. The cooling effect also protects people and property from the effects of radiated heat. By using the droplets’ shielding effect to reduce heat radiation, effective water mist shields can be generated for persons escaping from the fire and rescue teams as well as for components, wall openings, facades, etc.

Fire Chief Robert Triozzi, FRDP

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