Fog nozzle - AbsoluteAstronomy.com

A fog nozzle is a firefighting hose spray nozzle

Spray nozzle

A spray nozzle is a precision device that facilitates dispersion of liquid into a spray. Nozzles are used for three purposes: to distribute a liquid over an area, to increase liquid surface area, and create impact force on a solid surface...

that breaks the water that flows through it into tiny droplets of water. The theory is that small droplets

Spray characteristics

Spray nozzles are designed to perform under various operating conditions. The following characteristicsshould be considered when selecting a nozzle:* Spray Pattern* Capacity* Spray impact* Spray Angle* Drop Size- Spray Pattern :...

of water create more surface area

Surface area

Surface area is the measure of how much exposed area a solid object has, expressed in square units. Mathematical description of the surface area is considerably more involved than the definition of arc length of a curve. For polyhedra the surface area is the sum of the areas of its faces...

than a solid stream created by a smooth bore nozzle. The water absorbs the heat, turns into steam, and displaces the oxygen

Oxygen

Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

, smothering the fire

Fire

Fire is the rapid oxidation of a material in the chemical process of combustion, releasing heat, light, and various reaction products. Slower oxidative processes like rusting or digestion are not included by this definition....

. With the increase of surface area, this job is done quicker. Specially designed fog nozzles (with no stream adjustment) have been certified by Underwriters Laboratories

Underwriters Laboratories

Underwriters Laboratories Inc. is an independent product safety certification organization. Established in 1894, the company has its headquarters in Northbrook, Illinois. UL develops standards and test procedures for products, materials, components, assemblies, tools and equipment, chiefly dealing...

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

Roles

Fog nozzles play an important part in firefighting tactics. These types of nozzles are very versatile and can accommodate different sizes of fire hose

Firehose

A fire hose is a high-pressure hose used to carry water or other fire retardant to a fire to extinguish it. Outdoors, it is attached either to a fire engine or a fire hydrant. Indoors, it can be permanently attached to a building's standpipe or plumbing system...

and fire streams. They can be used for protection and for fire attack. When given the appropriate nozzle pressure and water supply

Water supply

Water supply is the provision of water by public utilities, commercial organisations, community endeavours or by individuals, usually via a system of pumps and pipes...

, they are effective for any fire ground situation.

Fog nozzles are typically used with fire attack hand lines. The fog nozzle that will be used on each size of fire hose is made to handle the maximum gallons per minute (GPM) rating that the fire hose can handle. There are fog nozzles that are used with master stream appliances also. A master stream can flow between 350gpm to 2000gpm. The fog nozzles placed on these types of appliances are made to handle that high of flow rate. Even with that high of flow rate, these fog nozzles are still made with spray pattern adjustments and in the automatic or manually adjustable styles.

One significant disadvantage is that they are less suitable for Compressed Air Foam (CAF) streams. CAF streams incoporporate bubbles produced by mixing air into a foam and water solution at the pump. The bubbles have a greater surface to volume ration than droplets produced by fog nozzles. When CAF is run through a fog nozzle, the mechanical deflection causes a loss of bubble structure, thus reducing the heat absorbing properties of the CAF.

There are many manufacturers of fire fighting nozzles.

Variations

Fog nozzles are made in different styles and sizes. The two main styles are the automatic fog nozzles and the manually adjustable fog nozzles. Both of these nozzles can be adjusted for the gallons per minute a firefighter needs to do the job. The automatic fog nozzle's rate of flow

Volumetric flow rate

The volumetric flow rate in fluid dynamics and hydrometry, is the volume of fluid which passes through a given surface per unit time...

is dependent on the water pressure delivered to the nozzle. Many firefighters rely on the stream shape to judge the flow rate of an automatic nozzle, this is incorrect. The automatic nozzle automatically compensates for variations in water availability. It works much like putting your finger on the end of a garden hose. The stream will maintain its reach in spite of fluctuations in flow. The reaction force felt by the firefighter will be in direct proportion to flow and serves as a very good indicator of total flow capability. Generally an automatic nozzle will deliver its rated flow range with a nozzle pressure that is plus or minus 15 psi of its rated pressure usually 100 psi, (This according the requirements of NFPA 1964) while the stream shape and reach will stay consistent. The flow rate will increase and decrease directly with the water pressure at the nozzle. The manually adjustable fog nozzle works differently in that the baffle which creates the orifice is manually adjustable. There is a direct comparison to a standard shift stick (the selectable nozzle) and an automatic transmission as used in vehicles. On selectable nozzles there is an adjustment bezel/ring that adjusts the opening of the nozzle much like the dial on the lens of a camera adjusts the opening of the lens. This selector bezel is around the tip of nozzle. There can be many different flow rates but a standard set of adjustments is 60gpm, 95gpm, and the 125gpm flow ratings at 100 psi. The firefighter

Firefighter

Firefighters are rescuers extensively trained primarily to put out hazardous fires that threaten civilian populations and property, to rescue people from car incidents, collapsed and burning buildings and other such situations...

can select one of these settings before or after the nozzle is opened. Once one of these gallon settings has been selected the nozzle will flow this rate only if the nozzle pressure is at the rated (100) psi value. This only occurs when the hydraulic calculations are correct such that there is a pump pressure in excess of the nozzle pressure by the amount of friction loss caused by the flow of the water. The automatic nozzle was invented by Clyde McMillan the founder of Task Force Tips on a napkin on May 10, 1968. His goal in inventing this nozzle was to simplify the calculations of the selectable nozzles that were in use at the time. As pressure increases the stream will be of high quality and have further reach, if the pressure decreases the opposite happens. Both of these nozzles allow the firefighter to make minor adjustments in the flow rate by opening and closing the bale (or control handle). The difference is that the selectable nozzle will change its nozzle pressure and reach as the handle is moved. The automatic nozzle on the other hand will automatically re-adjust its opening such that as the fire fighter changes the flow that can be handled the nozzle will resize itself to be the correct pressure. It works just like pressing on the gas in a car with an automatic transmission. You want to go fast you press on the gas and the car accelerates and shifts gears to match the power to the speed. WIth the automatic nozzle as you allow more flow thru the valve the automatic mechanism opens and closes to make sure that the pressure does not vary from the pressure that the nozzle was designed for..

Pattern

All styles of fog nozzles have a spray pattern adjustment. These nozzles can produce three different types of streams; the straight stream, the narrow-angle cone, and the wide-angle cone. Each of these types of streams is used for different purposes. The straight stream can be used for long reach. The narrow-angle cone can be used for advancing an attack line into a structure or the fire room. Protection and ventilation is the typical use of the wide-angle fog pattern. These types of spray patterns assist the firefighter in accomplishing his or her fire suppression efforts.

Roles

Variations

Pattern

See also