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What Are Water Mist Systems?

Posted by Lee Kaiser on Jan 8, 2018 8:00:00 AM

Water mist systems are becoming an increasingly popular alternative to total flood carbon dioxide systems, which can be dangerous to workers. With low, medium, and high pressure systems available, water mist systems can do everything from creating a fire suppressing fog to replacing traditional sprinkler systems. In this video, fire protection expert Lee Kaiser explains the basics of this safe and water-efficient fire suppression system.

VIDEO TRANSCRIPT

Lee: "So now, if CO2 systems are dangerous, what's an alternative to that?  What can we apply in its place? Well, that brings us to the point of talking about water mist systems. Water mist systems are one technology that can replace CO2 systems, so we'll start to talk through that. If you've never heard about a water mist system, water mist systems discharge water typically at high pressure through specialized nozzles to make a mist or even a fog of water in a space, and that fog has certain properties that help it to extinguish fires.  And we'll explain those. So all water mist systems result in very small droplets into the space or around the thing that they are protecting.

What is Water mist?

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. So the highest pressure water mist system I know of 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.

NOzzle and Water Types

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.

Droplet Sizes

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.

Why water Mist?

We see water mist growing because of these three reasons. 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, if they have a choice between water mist and carbon dioxide, and they have an active safety department and they care about the safety of their personnel, water mist system is going to be their choice a lot of times. We even see companies with existing total flood CO2 systems going and tearing them out and putting in water mist. 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."

Topics: Suppression, Fire Protection Services, Fire Protection Systems, Video Blogs

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