A fog nozzle is a

firefighting Firefighting is the act of extinguishing or preventing the spread of unwanted fires from threatening human lives and destroying property and the environment. A person who engages in firefighting is known as a firefighter. Firefighters typically ...

hose

spray nozzle A spray nozzle is a device that facilitates the dispersion of a liquid by the formation of a spray. The production of a spray requires the fragmentation of liquid structures, such as liquid sheets or ligaments, into droplets, often by using k ...

that breaks its stream into small droplets. By doing so, its stream achieves a greater

surface area The surface area of a solid object is a measure of the total area that the surface of the object occupies. The mathematical definition of surface area in the presence of curved surfaces is considerably more involved than the definition of arc ...

, and thus a greater rate of heat absorption, which, when compared to that of a smoothbore nozzle, speeds its transformation into the steam that smothers the

fire Fire is the rapid oxidation of a material (the fuel) in the exothermic chemical process of combustion, releasing heat, light, and various reaction Product (chemistry), products. At a certain point in the combustion reaction, called the ignition ...

by displacing its

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...

. Specially designed fog nozzles (with no stream adjustment) have been certified by

Underwriters Laboratories The UL enterprise is a global safety science company headquartered in Northbrook, Illinois, composed of three organizations, UL Research Institutes, UL Standards & Engagement and UL Solutions. Established in 1894, the UL enterprise was founded a ...

(UL) for use on Class B & C hazards.

Roles

Fog nozzles play an important part in firefighting

tactics Tactic(s) or Tactical may refer to: * Tactic (method), a conceptual action implemented as one or more specific tasks ** Military tactics, the disposition and maneuver of units on a particular sea or battlefield ** Chess tactics ** Political tact ...

due to their versatility. The wide variety of fog nozzle manufacturers allows them to accommodate different sizes of

fire hose A fire hose (or firehose) is a high-pressure hose that carries water or other fire retardant (such as foam) to a fire to extinguish it. Outdoors, it attaches either to a fire engine, fire hydrant, or a portable fire pump. Indoors, it can perma ...

—most often attack hand line—and streams and are capable in both fire protection and attack. With regard to flow rate, it is imperative to be sure that each fog nozzle be able to handle the flow rate of its water supply because the

master stream A deluge gun, fire monitor, master stream or deck gun is an aimable controllable high-capacity water jet used for manual firefighting or automatic fire protection systems. Deluge guns are often designed to accommodate foam which has been inject ...

devices to which they are sometimes attached can expel up to per minute. Nevertheless, as with almost all fog nozzles, those on master stream devices come with either automatic or manual spray pattern and stream adjustments. However, one significant disadvantage of fog nozzles is that the ratio of surface area to volume of the compressed air foam (CAF) bubbles (which are formed by mixing air into a solution of water and foaming agents at the pump) exceeds that of fog nozzles' water droplets; therefore, the mechanical deflection in the nozzles themselves causes a loss of bubble structure, thereby reducing the CAF's ability to absorb heat. Despite this drawback, provided an appropriate nozzle pressure and

water supply Water supply is the provision of water by public utilities, commercial organisations, community endeavors or by individuals, usually via a system of pumps and pipes. Public water supply systems are crucial to properly functioning societies. Thes ...

, fog nozzles are effective for any ground fire situation.

Variations

Fog nozzles come in many in different styles and sizes, but there are three types which encompass most: automatic, selectable, and manually adjustable. All contain an adjustable baffle that, like a thumb placed on the end of a garden hose, keeps their flow rates and stream reaches steady and finely adjustable despite variations in water pressure at the nozzle. To adjust the flow, the first two types use a control handle, or 'bale' located at the top of nozzle; however, selectable nozzles have a fixed set of flow rates (e.g., 60, 95, and 125 GPM (gallons per min)) that are chosen with a ring or bezel located at their tips. It is important to note that selectable nozzles will only flow if the pump pressure exceeds the nozzle pressure. Moreover, the selectable nozzle will change its nozzle pressure and reach as the handle is moved, but the automatic nozzle will automatically re-adjust its opening as the firefighter adjusts its flow rate in order to maintain the correct pressure.

Pattern

All styles of fog nozzles have a spray pattern adjustment. These nozzles can produce three different types of streams; the straight stream for long reach, the narrow-angle cone for advancing an attack line into a structure or fire room, and the wide-angle cone for protection and ventilation.

Images

Image:Fog nozzle5.JPG, Automatic 1½" Fog Nozzle Image:Fog nozzle7.JPG, Manually Adjustable 1½" Fog Nozzle Image:Fog nozzle4.JPG, Manually Adjustable 2½" Fog Nozzle Image:Fog nozzle11.JPG, Automatic Master Stream Fog Nozzle Image:Fog nozzle3.JPG, Automatic 2½" Fog Nozzle

References

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External links