Watermist Fire Suppression Systems

How Do Watermist Fire Suppression Systems Work?

Watermist fire suppression systems use specially designed nozzles to release fine water droplets onto or around a fire. These droplets absorb heat and help control, suppress or extinguish the flames. As a result, water mist can provide effective fire protection while using less water than some conventional sprinkler systems.

Water mist works in several ways. First, the droplets absorb heat from the fire and surrounding gases. As the water evaporates, the resulting steam can also reduce the oxygen available near the flames. In addition, the mist can reduce heat transfer to nearby materials, helping to limit fire spread.

However, the balance between cooling and oxygen displacement depends on the fire, droplet size and system design. Therefore, watermist systems must be selected and designed for the specific hazards they need to protect.

Businesses may consider watermist fire suppression for suitable machinery, industrial processes, equipment enclosures and other commercial environments. Some systems can also protect particular electrical or flammable liquid hazards, provided the equipment has appropriate evidence of performance for the intended application.

Types of Watermist Fire Suppression Systems

Watermist systems use different nozzle arrangements and water supplies depending on the area requiring protection. The main options include open-head and closed-head systems, together with cylinder-based or pump-driven water supplies.

Open-Head Watermist Systems

Open-head systems use nozzles that remain open rather than relying on individual heat-sensitive bulbs. When the fire detection and control system activates the appropriate release valve, water flows through the nozzles in the relevant protected section.

These systems can provide protection for selected machinery, equipment enclosures and other applications where a coordinated discharge is appropriate.

Closed-Head Watermist Systems

Closed-head systems use nozzles fitted with heat-sensitive elements, often glass bulbs. When heat from a fire raises the temperature sufficiently, the element activates and allows water to flow through that nozzle.

This arrangement works in a similar way to a conventional sprinkler head. However, the nozzle design and watermist performance requirements differ from those of a standard sprinkler system.

Cylinder-Based Watermist Systems

Cylinder-based watermist systems store a supply of water in dedicated cylinders. Depending on the design, compressed gas such as nitrogen provides the pressure needed to discharge the water through the system.

These systems can suit smaller or localised risks where a compact, self-contained water supply offers a practical solution. Installers can position the cylinders close to the protected equipment, subject to the system’s design requirements.

Pump-Driven Watermist Systems

Pump-driven watermist systems use pumps to deliver water at the pressure required by the nozzles. Depending on the installation, the system may draw water from a dedicated storage tank or another suitable water supply.

These systems can protect larger areas or provide longer operating periods where the design requires them. In addition, the installation may need a reliable electrical supply, backup power arrangements and appropriate water storage capacity.

The designer must determine the required water supply, operating duration, pump arrangement and applicable standards for the specific system. Watermist installations generally fall under the BS EN 14972 series, rather than automatically following the sprinkler requirements of BS EN 12845.

Watermist System Valves

Control and section valves manage water flow within a watermist system. For example, they may direct water to a particular protected area or isolate part of the installation for maintenance.

The type and arrangement of valves depend on the system design, the protected hazards and the required method of activation.

Advantages and Applications of Watermist Fire Suppression

Watermist fire suppression systems offer several benefits for commercial and industrial premises. By releasing fine water droplets, they can control fire, reduce heat and help limit fire spread. In addition, suitable systems may use less water than conventional sprinkler installations.

Advantages of Watermist Fire Suppression Systems

• Reduced water consumption: Many watermist systems use less water than conventional sprinklers. As a result, they may reduce the amount of water released during a fire.
• Effective cooling: Fine water droplets absorb heat quickly, helping to control flames and reduce the risk of fire spreading to nearby materials.
• Flexible activation: Depending on the design, systems can use heat-sensitive nozzles, automatic fire detection or manual release controls.
• Targeted protection: Local application systems can protect individual machines, equipment enclosures or other identified hazards without covering an entire building.
• Compact installation options: Some cylinder-based systems require relatively little storage space and pipework, making them suitable for smaller protected areas.
• Reduced reliance on chemical agents: Watermist systems use water as the main extinguishing medium. Therefore, they avoid the need for some specialist chemical extinguishing agents.
• Separate protection zones: Certain systems can protect different areas independently through suitable detection, valves and controls.
• Adaptable water supplies: Installers can select cylinder-based or pump-driven arrangements according to the size and needs of the installation.
• Suitable for specialist applications: Where testing and system approval support the intended use, water mist can protect selected machinery, electrical equipment and industrial processes.

Considerations and Limitations of Watermist Systems

Although watermist systems offer several advantages, they are not suitable for every fire risk. Therefore, businesses should consider the following factors before choosing a system.

• Application-specific performance: Watermist effectiveness depends on the fire hazard, nozzle arrangement, water pressure and system design. A system must have suitable evidence of performance for the intended application.
• Potential water damage: Water mist uses less water in many applications, but discharge can still affect sensitive equipment, stored materials and electrical installations.
• Water supply requirements: Larger installations may need dedicated tanks, pumps and reliable water supplies. Consequently, installation costs can vary considerably.
• Power requirements: Pump-driven systems may need a suitable electrical supply and backup arrangements to maintain operation during an emergency.
• Maintenance: Nozzles, filters, valves, pumps and water supplies need appropriate inspection and maintenance to ensure reliable performance.
• Standards and approvals: Watermist systems should follow applicable requirements, including the relevant parts of the BS EN 14972 series and appropriate fire test protocols.
• Not a universal sprinkler replacement: Watermist systems cannot automatically replace conventional sprinklers. The proposed design must meet the requirements of the protected risk and any relevant insurer or approving authority.

Typical Applications of Watermist Fire Suppression

Watermist fire suppression can provide protection across a range of commercial and industrial settings. However, the suitability of each application depends on the system’s tested performance and the specific fire hazards present.

• Machinery spaces: Protection for suitable mechanical equipment and industrial machinery.
• Data and equipment rooms: Selected applications involving electronic equipment, where the system has appropriate evidence of suitability.
• Generators and equipment enclosures: Local application protection for suitable generators, machinery cabinets and enclosed equipment.
• Commercial kitchens: Specialist watermist systems may protect certain cooking appliances, provided they are specifically tested and approved for the cooking hazards involved.
• Industrial test facilities: Protection for selected test cells, machinery and specialist processes.
• Archives and storage areas: Fire protection for suitable storage environments where reducing water use may offer benefits.
• Spray booths: Protection for certain spray processes where the system has suitable test evidence for the fire hazards involved.

SS Systems can discuss your fire protection requirements and help you explore suitable watermist fire suppression options. By assessing the hazards, equipment and layout of your premises, we can help identify an appropriate solution for your business.