A Deep Dive on Water Mist Fire Protection Systems: Safe, Effective and Environmentally Sustainable Solutions

Water mist technology was first introduced in North America in the early 1990s. It has since proven to be highly effective at fire suppression, gaining credibility and recognition as a viable alternative to traditional sprinkler systems in commercial buildings. As both control and suppression mechanisms and water mist features have become better understood over the past decade, the use of this technology has expanded to a range of land-based applications including museums, hotels, data centers, hospitals and skyscrapers.

HOW IT WORKS

The Society of Fire Protection Engineers (SFPE) Handbook of Fire Protection Engineering refers to three primary and two secondary mechanisms in the extinguishment/suppression process.  The primary mechanisms are:

Gas phase cooling

• Oxygen depletion and flammable vapor dilution
• Wetting and cooling of the fuel surface

The secondary mechanisms are:

• Radiation attenuation
• Kinetic effects

The wider acceptance of water mist systems is primarily due to their ability to fight both solid- and liquid-based fires in a more efficient manner than traditional sprinkler systems using more of these mechanisms. The technology targets the two main elements fire needs to survive, heat and oxygen, by discharging water at a high velocity through lightweight, small diameter stainless steel tubes and specially designed sprinklers. The result is a mist consisting of fine droplets that have significantly greater specific surface area (surface area per unit mass of water) and heat-absorbing capacity compared to water dispensed from low pressure water mist systems and traditional sprinkler heads. The water droplets vaporize more efficiently, which reduces oxygen available at the fire source, thus enhancing fire suppression.

This method of fire protection also blocks radiant heat, preventing the fire from spreading, and protecting the surroundings from the heat. Water mist systems are highly efficient in controlling fire, using significantly less water than traditional sprinkler systems. Fire tests comparing water mist systems with traditional sprinkler systems show that Marioff’s HI-FOG® high pressure water mist system used up to 90 percent less water to bring the same fire under control. This feature makes water mist systems more environmentally sustainable than traditional sprinkler systems.

TYPES OF WATER MIST SYTEMS

There are two predominant types of water mist system in the North American market: high pressure (>500 psi) and low pressure (175 psi or less). High pressure systems use less water than low pressure systems and consume significantly less water than traditional sprinkler systems to effectively control and suppress fires.

One of the primary advantages of water mist systems is flexibility; engineers, architects and contractors can select different tubing, valves and nozzles depending on the application and fire risk. Therefore, a water mist system can be a single configuration or a mixture of several configurations. The most common configurations are:

• Wet pipe system
  This is the most common type of system as it is both economical and easy to operate for both medium and large-sized areas. The system uses closed, heat-activated sprinkler heads with activation bulbs that operate when the ambient temperature at the sprinkler head exceeds the prescribed temperature rating. Wet pipe system applications can include hospitals, shopping centers and factories.

• Deluge system
  This system typically has open spray heads and a closed-type valve to control water flow. When the valve opens, water mist discharges from all of the spray heads in the area controlled by that valve. The deluge system is commonly used to protect machinery spaces, as it provides full, homogeneous defense against fire. 

• Dry pipe system
  This system operates much like a wet pipe system, but the section valve keeps the water on the pump side of the tubing in normal operation and the tubing from the valve to the sprinklers is filled with compressed air or nitrogen, which is monitored. This system is typically used when the protected area is subject to freezing temperatures, such as unheated buildings and parking garages.

• Pre-action system
  This system employs the basic concept of a dry pipe system. The difference, however, is that it is connected to a fire detection system and usually protects areas where the risk of accidental discharge needs to be minimized. This type of system is ideal for buildings with valuable collateral, such as museums and large data centers. 

Water mist systems are designed on a performance basis, and thus, in order to maintain system integrity, a system should never be designed using one manufacturer’s system and another manufacturer’s test results. The complete system offering also should be fully fire-tested for a given application. Systems such as Marioff’s HI-FOG are designed in accordance with the company’s comprehensive range of approvals. In other cases HI-FOG is designed on a project-by-project basis according to results from fire tests supervised and witnessed by third parties. In most cases, system designs must be approved by local fire officials or authorities.

In an office building, for example, the main configuration could be a wet pipe system, while a pre-action system protects the computer server room and a deluge system protects back-up generators. The same pump unit would serve all the configurations.

EASY INSTALLATION

High pressure water mist systems are easily customizable and feature small, bendable stainless steel tubing that is more adaptable than piping in traditional sprinkler systems, making installation simpler, especially in older buildings with tighter spaces. The flexible and lightweight nature of high pressure water mist system tubing requires less volume, is quick to install and is easy to maneuver around unique angles, corners and architectural obstructions. The piping network is small enough to be hidden from view, using a variety of design elements, such as crown molding to preserve the building aesthetics.

The placement of high pressure water mist systems’ sprinkler and spray heads in a building is decided according to system design guidelines, application-specific fire tests, local fire regulations and the building’s technical requirements. A control system, panels, release devices, compressors and other equipment can be added as required. The systems use a separate water supply from a main feed or a dedicated water tank.

Pump units for water mist systems can include gas-driven, electric and diesel. All tubing in the high pressure parts of the system are made of stainless steel and are much smaller than the black iron piping systems typically used in traditional sprinkler systems.

WATER DAMAGE CONTROL

An additional benefit of water mist systems is the fact that these systems mitigate property water damage that can occur following a system activation. 

When a fire occurs in a hotel, traditional sprinkler systems can drown the hotel floors with approximately 2,200 to 3,350 gallons of water per room —damage that can take weeks or even months to repair. Water mist fire protection systems, however, can control or suppress a fire 10 times more efficiently with only 105 to 285 gallons of water per room by releasing water mist at a high velocity that consists of fine droplets. These smaller droplets also vaporize more water, which reduces the concentration of oxygen available at the flame source to promote fire suppression. The mist is an added safety benefit as the smoke is essentially “scrubbed” while controlling and suppressing a fire, offering better protection to building occupants, first responders and the property itself.

Mold is another concern that results from water damage and is more prevalent when using traditional sprinkler systems. Mold can cause serious problems like lung and eye irritation, allergies, asthma attacks and sinus congestion. If a building has water damage, it takes only 24 to 48 hours for mold to start developing. In contrast, HI-FOG causes minimal water damage following a fire, reducing the total cost of ownership for commercial building proprietors.

WIDER ACCEPTANCE

When water mist fire protection technology launched in North America more than a decade ago, system manufacturers educated key influencers through live product demonstrations and data-outcome presentations. Subsequently, architects, engineers, contractors and building owners began incorporating the technology into proposed building designs.

In December 2011, the technology achieved a critical milestone when HI-FOG^- became the first water mist fire protection product to receive Underwriters Laboratory (UL) listing for Ordinary Hazard Group 1 (OH1) applications. This, together with HI-FOG’s Factory Mutual (FM) Light Hazard (LH) system approval, has paved the way for water mist to provide a complete fire protection solution for a range of commercial buildings including data centers, high-rise buildings, hospitals, cultural heritage sites and hotels.

ABOUT THE AUTHOR

Lance D. Harry, P.E. is General Manager, Marioff North America. Mr. Harry has been extensively involved in designing, developing, testing and deploying water mist systems around the world. With thousands of full-scale fire tests completed, the HI-FOG Water Mist Fire Protection System is the world’s most tested water mist solution. HI-FOG has been tested across a wide variety of applications and holds a large number of type approvals from recognized approval authorities.

About Marioff and HI-FOG^®

Marioff is the leading developer of water mist fire protection technology and supplies system solutions worldwide. The company designs and manufactures all key components of the water mist fire protection system under the name HI-FOG. The HI-FOG water mist fire protection system is a modern, highly effective solution suitable for most types of fires, on land and at sea. It safely controls and suppresses fire by discharging a fine water mist at high velocity. It uses up to 90 percent less water than traditional sprinkler systems. Less water means less water damage, and less clean-up time, significantly reducing operational downtime.      

Marioff is part of UTC Climate, Controls &  Security Systems, a unit of United Technologies Corp., which provides high technology products and services to the building and aerospace industries worldwide. More information about Marioff can be found on its website at www.marioff.com.