Fog nozzles break water into droplets and distribute them as a fog, with spray characteristics that vary in length and width. They can be used indirectly or as a combined method of fire extinguishing. The spray cools the area and extinguishes the flames simultaneously.
A common piece of firefighting equipment, a fog nozzle mechanically breaks water into fine droplets and distributes them as a fog. Automatic or manual nozzle adjustment creates spray characteristics that vary in length and width. Trained firefighters use each spray pattern from a fogger nozzle under different conditions.
Firefighters typically use fog nozzles with hand hoses. Water flows through these pipes at speeds ranging from 60 to 180 gallons (227 to 681 liters) per minute. The force of the water hitting the special diffusing element inside the misting nozzle transforms the droplets into vapor-like particles. The vapor produced resembles a moist mist and covers a larger surface area than a single stream of water.
An automatic spray nozzle generally adjusts the length and width of the jet it emits based on the water pressure. Manual sprinklers have a handle that firefighters use to adjust the spray regardless of water pressure. The nozzle can be adjusted to emit a straight stream of water, a narrow angle cone or a wide angle cone. Narrow angle fog can also contain a central stream of water. The wide-angle fog not only covers a larger area, but also acts as a shield to protect advancing firefighters.
The spray from a mist nozzle is aimed at strategic areas of a burning room. The fog absorbs the heat generated by the fire and becomes vapor, displacing the oxygen required by the fire and extinguishing the flame. A fogging nozzle can be used indirectly or as a combined method of fire extinguishing.
The indirect method requires that the ceiling temperature be a minimum of 1,000 degrees Fahrenheit (537 degrees Celsius). This amount of heat ensures that the mist emitted from the hose’s spray nozzle is instantly converted into vapor. Ideally, the room should be closed off to keep the steam in that location. Lack of ventilation prevents outside air from entering the room and fueling the fire. The combined method involves cooling the area and extinguishing the flames simultaneously.
Using the fog nozzle, firefighters typically direct the spray around the perimeter of the room. The mist hits and cools the ceiling, walls and floor, while the vapor generated smothers the flame. A central water jet can also be used to cool the hot steam and extinguish the flames at the source.
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