Traditional automatic sprinkler system has been around for almost a century and can be found in all types of buildings. This system is required by fire codes across the globe, but, surprisingly, there have been very little improvement since its beginnings. A new fire protection method has emerged relatively recently, which uses water mist to suppress fires. The manufacturers claim to outperform the traditional system in each and every aspect, but are they able to transform the industry?

A brief history

Figure 1. A water mist sprinkler system in a warehouse. Source: WisprexFigure 1. A water mist sprinkler system in a warehouse. Source: Wisprex

The idea of using high pressure water mist for fire suppression is not new. It was invented over 130 years ago, in the form of a backpack with a lance that produced water droplets, to fight small forest fires. The development of this system continued throughout the last century, but the technology was not commercially viable as it did not meet the requirements for fixed installations at the time. It was not until 1990s when the technology really took off due to two main events. First, Montreal Protocol initiated the phasing out of Halon which was widely used in marine and aviation markets. Second, a fire incident occurred on the passenger ferry ship in Sweden in 1990, killing 158 people. This forced the industry to look for alternatives, and the water mist system was one of the best candidates.

The system quickly gained popularity, and a new standard was necessary to make it suitable for fixed installations. With an active involvement of the pioneering manufacturers, NFPA 750 standard was established, which covered testing, design, components and categories of water mist systems.

Working principle

Water mist fire protection system works in a similar fashion to traditional sprinkler system. The main difference is that it discharges water at a much higher pressure through special nozzles, which creates extremely fine mist of micro-droplets. These tiny droplets efficiently penetrate the flame, cool the surrounding air and block radiant heat, in this way containing and extinguishing the fire.

A typical water mist system consists of the following:

· High-pressure pump unit

· Small water supply tank

· Section valves

· Small-diameter stainless steel tubing

· Sprinkler or spray heads

As defined in NFPA 750, system pressures range from low (below 12.1 bar) to high (above 34.5 bar). There are installed systems that were designed to pressures as high as 158 bar, which require specialized piping. High pressures are generated by the pump units, which may be electric, diesel or compressed gas driven. The latter uses pressurized air or nitrogen stored in the cylinders mounted on the same skid as the pump.

Section valves in water mist systems are used in the same way as zone control valves in traditional systems. Their function is to isolate sections for maintenance purposes, monitor the flow and indicate to the system that a sprinkler head has been activated.

Sprinkler heads operate in a similar way to traditional system as well. They are fitted with a heat-sensitive glass bulb, which releases the spool valve allowing high-pressure water to flow through micro-nozzles. Spray heads are also available which are activated directly through an independent fire detection system.

Comparison to a traditional sprinkler system

Although there are many similarities in the components of the two systems, there are big differences in the value that each system brings to building owners. The main differences are listed below:

1. The water consumption in the mist system is typically only a tenth of an equivalent traditional sprinkler system. This is a significant saving in terms of water usage, which also mans a much smaller storage tank.

2. The distribution pipework in the mist system has much smaller diameters than in the traditional system, because of much lower flow rates. In a typical project, around 75% of pipework will have a diameter of only 12 mm. In contrast, traditional system has a minimum pipe diameter of 25 mm connecting two sprinklers, and pipe diameters of up to 200 mm for the main pipe runs.

3. Mist system produces much less damage to a property than a traditional one and requires less clean-up, as very little water is discharged into space. This aspect is important to building owners as the disruption caused by the fire is minimal.

4. Mist system is designed to both control and extinguish fires, unlike traditional system which is designed to simply prevent the spread of fire until the fire brigade arrives. This puts water mist system under the class of special hazard fire suppression systems along with clean agents, inert gases and CO2. This means that it can be used for the fire protection of data centers and similar environments. When compared to gas suppression system, mist system does not require an air-tight room which involves expensive sealing and testing. In addition, it does not require additional space to store gas cylinders and avoids installation of gas purge systems.

5. Mist system is more expensive to design and install than a traditional one, since high-pressure systems require more sophisticated components and materials of higher quality. Manufacturers of such systems typically provide a turnkey solution (i.e. design, installation, supply of equipment and maintenance) as specialist input is required throughout the whole life cycle of the system.

Project costs

It is true that cost is the main factor that influences the choice of different systems. Water mist system clearly brings more value to building owners in terms of operation and maintenance, but the initial expenditure is higher.

However, it would not be correct to compare the two systems in terms of just capital cost. The benefits that the mist system brings should be quantified in the context of the whole project savings.

For instance, in buildings with sufficient number of rooms that require gas fire protection (i.e. data centers and rooms with high value assets), the mist system becomes competitive if looking at the total project cost. Large amount of savings will come from avoiding installation of gas suppression and gas purging systems as well as sealing each room. It is also much cheaper to operate and maintain one single system for the whole building rather than multiple systems. Additional space created by omitting gas cylinders can also be used to increase net available areas in commercial buildings.

Installation of mist systems might sometimes be the only acceptable solution for fire protection where space is limited. Due to small pipes, the system can fit in shallow ceiling voids and avoid clashes with other building services. Suitable applications are hospitals where ceiling voids are typically very congested, or retrofit projects where it is essential to not disturb existing installations.


When it comes to fire protection, a traditional sprinkler system has long been the only option for building owners. Its recent successor - the water mist system - has been gaining popularity in the last three decades because of its effectiveness and flexibility. The main obstacle for this system to become the first choice in most projects is its capital cost. However, the indirect savings and benefits that this system brings to building owners may prove the higher cost feasible.