What is condensed aerosol fire suppression?

Condensed aerosol fire suppression, a relatively new technology, is a system of aerosol containers or a single container, that are interconnected to each other and to a control panel, designed to extinguish fires in special hazard applications. Other special-hazard fire-protection systems including dry chemical, wet chemical, gaseous clean agent (halocarbon or inert gas), water mist, carbon dioxide and, in the past, halon systems are also used in similar applications.

Special-hazard applications are those that are not appropriate for automatic sprinkler protection, either due to the fire hazard itself, or the contents that are being protected. Automatic sprinkler systems can damage sensitive IT equipment, and even wet chemical systems, used to protect commercial cooking operations, can damage cooking equipment, and offer clean-up challenges.

Unlike other special-hazard systems, condensed aerosol suppression systems do not require a separate vessel for the agent itself, nor do they require an interconnected piping network to deliver the agent. Condensed aerosol systems operate by smoke or heat detection, together with control panels, thermally activated, or manually operated with pull stations.

Condensed aerosol fire suppression can also be used for small, local protection, such as providing fire suppression for electric cabinets or vehicle engines. Finally, condensed aerosol fire suppression can be used in portable fire extinguishers or as modules to be thrown into fire areas by first responders to suppress flames before they enter the enclosure. Figure 1 below illustrates a condensed aerosol nozzle discharging its agent to suppress a fire.

How does condensed aerosol fire suppression work?

Despite the ‘fire triangle’ discussed as early as elementary school (Figure 2), this model does not fully explain how a fire initiates and continues to burn.

The traditional fire triangle illustrates that heat, a fuel source, and oxygen are required for a fire to propagate.

There is a fourth element, often not discussed, that is also required for a fire to propagate: an unmitigated chain reaction. This chain reaction is mostly the propagation of hydrogen ions reacting with other chemicals to produce heat. Figure 3 below illustrates the fire tetrahedron. A tetrahedron is a solid constructed of equally sized triangles and is the simplest three-dimensional object possible in geometry.

It is important to keep this tetrahedron in mind because condensed aerosol fire suppression extinguishes or suppresses fire primarily by disrupting the chemical chain reaction.

Disrupting the chemical chain reaction of a fire is considered the most effective method of fire suppression, and this is why halon systems, which suppress a fire in the same way, were considered one of the most effective fire-suppression systems. Halon and other chemicals like it were banned by the Montreal Protocol in the 1990s and are only permitted for military use. Additionally, the United States Environmental Agency (EPA) has approved condensed aerosols for use in fire-suppression systems.

The sequence of operation is as follows:

1. The aerosol container is sealed until it is automatically or manually activated.
2. The actuator at the top of the aerosol container energizes a proprietary compound, which creates aerosol agent by liberating energy.
3. A mixture of micro-particles and nitrogen gas exits the container.
4. Small amounts of gas and particles fill the space and extinguish the fire as described above.

The condensed aerosol pellet contains a proprietary mixture of chemicals which varies between brands.

Codes and standards

NFPA 2010: Standard for Fixed Aerosol Fire-Extinguishing Systems is the primary standard that is used to design, install and maintain fixed aerosol systems. This standard applies to the fixed systems that are used to protect stationary hazards, such as electrical cabinets and electrical switchgear rooms. The standard that governs the requirements of the components used within condensed aerosol systems is UL 2775: Standard for Fixed Condensed Aerosol Extinguishing System Units.

NFPA 2010 may be viewed for free online at: www.nfpa.org/codes-and-standards/all-codes-and-standards/list-of-codes-and-standards/detail?code=2010

UL 2775 may be viewed for free online at: standardscatalog.ul.com/ProductDetail.aspx?productId=UL2775

For more information, please visit: www.statx.com/fire-education