CHOOSING THE RIGHT NOZZLE

CHOOSING THE RIGHT NOZZLE

VOLUNTEERS CORNER

There is a wide range of nozzles available for firefighting today. For many years firefighters used a solid bore nozzle; then came the advent of the fog or spray nozzle, which was automated in terms of a constant nozzle pressure. A recent product is a nozzle with a solid bore and a detachable fog tip.

Foam nozzles have been used for fighting flammable liquid fires, and master stream devices have delivered large quantities of water through either solid bore or fog tips. A fog tip or head divides the water up into fine droplets, creating a spray, while a straight stream is defined as the most narrow pattern of a fog nozzle and should not be confused with the solid stream delivered by a solid bore or straight tip nozzle.

The most commonly used nozzle is some type of fog nozzle—constant flow, variablc-gallonage constant flow, or automatic. There are also low-gallonage, high-pressure fog nozzles. Automatic nozzles can deliver as much as 350 gpm on a handline. There is concern in some areas that the fog nozzle is creating problems for firefighters during structural fire attack.

Before discussing fog vs. solid bore, let me emphasize that the use of fog streams on high flash point flammable liquids such as fuel oil and on flammable gases where a wide pattern provides protection is not in question. Foam nozzles are also for use on low flash point flammable liquids such as xylene and in vapor supression operations. However, recently foam has proved very effective in wildland firefighting, even in concentrations of less than one percent. Also, smallcaliber solid bore nozzles are very effective for reach and penetration during wildland operations.

The real question here is a which combination of nozzle tip and interior structural attack procedures to use. With a fog nozzle, the fire attack is initiated at the ceiling level over the fire with a 30° pattern to obtain the immediate conversion of the water to steam in the superheated atmosphere. The stream is then rotated to cool and smother simultaneously. With this action the firefighter soon finds the only tenable area is at floor level. The steam not only causes burns to a standing firefighter but also creates zero visibility conditions.

It is important to understand how the water discharged from a fog nozzle at a 30° or wider setting works. The water is emitted in a fine spray to increase surface area and consequently rapid absorption of heat. The idea is to direct an adequate quantity of water broken into fine droplets into the superheated ceiling area. As the water absorbs heat (it only takes see-, onds), it is of course cooling the atmosphere and at the same time expanding. This expansion pushes the air out of the area and assists in fire suppression by excluding the oxygen. The room or area is now filled with steam or water vapor at a temperature of 212°F. This is below the ignition temperature of most ordinary combustibles (cooling), and the oxygen has been driven out (smothering).

A major problem is that the fire service seems to have forgotten how to use the steam conversion of a fog nozzle in firefighting. Firefighters want to walk into a burning structure and use the nozzle from a standing position or while in a doorway. It is no wonder they get burned when the steam is generated —even a crouch can be too high! They also want to pour excessive water on the fire using the theory that if a little water cools, a lot will extinguish faster. However, too much water spray upsets the thermal balance and creates a rolling cloud of steam that rolls from the ceiling level down to the floor and then back up to the ceiling.

A proper attack with a fog line should be made by going in low. This could mean crawling on your stomach when necessary, since crawling on your hands and knees can be too high. When you reach the fire area, direct the stream into the superheated area above the fire until the fire blacks out. Then shut the nozzle off and drop to the floor flat. Slowly count to 15, allowing the steam to lift a little. If the fire begins to come back, hit it again with a short burst. Too much water application by not shutting the nozzle off as soon as the fire is knocked down will lead to thermal imbalance and a lasting loss of visibility. Spot fires subsequently can be extinguished with short bursts from a straight stream. This type of attack generates steam that will penetrate into concealed spaces and often extinguish hidden fire.

Fog streams also can be used to push heat ahead of advancing firefighters and provide protection against heat —for example, in a rollover situation. A wide-angle fog will absorb considerable heat. This can protect the firefighters on the line if the nozzle is opened to a wide enough pattern.

Solid streams are used in a direct attack on the burning material. They extinguish by cooling the material below its ignition temperature. There is generally little steam buildup, which lessens the chance of steam burns and improves visibility. The longer reach of the solid bore stream enables firefighters to stay farther back from the fire as long as they can see it—solid streams generally are limited to line-of-sight use. Thus the nozzle operator must be able to see the burning material in order to hit it with the stream of water. Once the material is cooled, there is no longer the generation of gases to support combustion. These nozzles work at a lower tip pressure, making the hoseline easier to maneuver. A solid stream will provide little protection against heat. A fog nozzle in a straight stream setting always can be opened to a wider pattern to provide increased protection. Since the stream is not broken up as much as a fog stream (solid streams are broken up by bouncing them off the ceiling or a wall), they do not use water as efficiently. The advantages are long reach, penetration capabilities, and lack of steam generation.

Both types of tips are used on master stream devices. The fog tip has limited reach, so it is only good for exposure protection when the distance is not great. It can be an effective fire suppressant when the fog stream is introduced through a window or opening into the building, making a large-gallonage application of a finely divided spray. However, since master streams are most often used in defensive operations, the solid bore tip may be more advantageous. The stream can be positioned a greater distance away from the structure, providing greater protection from radiated heat and collapse. When positioned back, the solid stream has greater penetration capability due to the larger water droplets. These drops are not as easily influenced by the wind, thermal column, or heat. Smaller drops usually are evaporated by the heat before they reach the fire and can do any cooling. The longer reach of the solid stream is also advantageous for protecting larger exposures. As a general rule, the solid bore nozzle has more applications on a master stream device.

How do you decide which nozzle to use? Study the types of fires that you have and determine which tip is most suited to your applications. Perform tests during training exercises and live burn drills. Check each nozzle in terms of maneuverability, reach, exposure protection, steam generation, visibility, and effective fire extinguishment.

Perhaps the best solution is to set up the hoseloads for an initial attack using both types of nozzles. Then either can be used depending on the situation on your arrival. This lends versatility to your apparatus and increases your efficiency as a fire suppression organization.

Above all, train your firefighters to use both types of nozzles in the various situations that may demand them. 1’he correct nozzle is useless without a well-trained firefighter who knows how to effectively apply an extinguishing stream to the particular type of fire.

Paul Dansbach and Glenn Corbett

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