fire science chapter 16 fire streams

types of fog nozzles

1. basic fog nozzle - adjustable pattern fog nozzle in which the rated discharge is delivered at a designated nozzle pressure and setting 2. constant gallonage fog nozzle - an adjustable pattern fog nozzle that discharges a constant discharge rate throughout the range of patterns 3. constant pressure (automatic) fog nozzle - an adjustable-pattern fog nozzle in which the pressure remains relatively constant through a range of discharge rates 4. constant/select gallonage fog nozzle - a constant discharge rate fog nozzle with a feature that allows manual adjustment of the orifice to effect a predetermined discharge rate while the nozzle is flowing. depending on the size of the nozzle, the operator may adjust flow rates from 10gpm to 250gpm for hand lines and from 350 to 2500gpm for master streams. abrupt changes in the reaction force of the hose line may throw FFs off balance and so adjustments to flow rate should be made slowly. constant pressure fog nozzles automatically vary the rate of flow to maintain reasonably constant nozzle pressure through a specified flow range. the nozzle operator can change the rate of flow by opening or closing the shutoff valve. automatic fog nozzles for hand lines are designed for the following flow rates: -low flow such as 10gpm to 125gpm -mid range flows such as 70-200gpm -high flows such as 70gpm to 350gpm automatic master stream fog nozzles are typically designed to flow between 350 and 1250gpm. fog nozzles are designed to operate at a variety of nozzle pressures. the designed operating pressure for most fog nozzles is 100psi.

fire stream nozzles

NFPA 1963, standard for fire hose connections established two general categories of fire stream nozzles: straight tip nozzles (smooth bore) and spray nozzles (fog nozzles). smooth bore and fog nozzles are used on hand lines and on master stream appliances such as fixed apparatus-mounted monitors, portable monitors and elevated monitors mounted on aerial devices. both categories of nozzles as well as the broken stream delivery devices perform three main functions: controlling water flow, creating reach and shaping the fire stream

fire stream patterns, nozzles and control valves

a fire stream is a stream of water or other extinguishing agent after it leaves a fire hose nozzle until it reaches the desired target. the size of the nozzle opening or orifice and nozzle pressure determines the quantity of water flowing from the nozzle. at the same time, the size of the opening also influences the reach or distance of the fire stream. finally, the type of nozzle determines the shape of the fire stream. a smooth bore nozzle produces a tightly packed solid stream of water. a fog nozzle produces a fog or straight stream

broken stream delivery devices

can be used to extinguish concealed space fires such as those found in basements, chimneys, attics, or other types of concealed spaces. the special nozzles that can be used to produce a broken stream include: -piercing nozzles: used to access fires in concealed places. can be used to pierce material such as stucco, block, wood, and lightweight steel -cellar nozzles: consists of a rotating head with multiple outlets that distribute water in a circular pattern. the nozzle may be supplied by a 1.5in or 2.5in supply hose with a control valve located one section of hose from the nozzle. two common cellar nozzles are the Bresnan distributor and the Rockwood cellar pipe

smooth bore nozzles

designed so that the shape of the water in the nozzle is gradually reduced until it reaches a point a short distance from the orifice. *the smooth bore nozzle tip should not be larger than one-half the diameter of the hose characteristics of smooth bore nozzles include: -operate at low nozzle pressures -are less prone to clogging with debris -can be used to apply compressed-air foam -may allow hoselines to kink due to less pressure -do not allow for selection of different stream patterns the velocity of the stream is a result of the nozzle pressure. when smooth bore nozzles are used on hand lines, they are usually operated at 50psi nozzle pressure. most smooth bore master stream appliances are operated at 80psi

fog stream

fine spray composed of tiny water droplets. fog nozzles are used to produce fog streams designed to permit adjustment of the tip to produce different fog-stream patterns. water droplets, in either a shower or a spray, are formed to expose the maximum water surface for heat absorption. the desired performance of a fog stream is characterized by the amount of heat that it absorbs and the rate by which the water is converted into steam or vapor. fog streams have the following characteristics: -patterns can be adjusted to suit the situation -can be used for hydraulic ventilation -can be used for vapor dispersion -can be used for crew protection -reduce heat -used to cool the hot fire gas layer as well as hot surfaces -shorter reach or penetration than solid or straight streams -are more affected by wind than are solid or straight streams -may disturb thermal layering in a room or compartment if applied incorrectly -may intensify the fire by pushing fresh air into the fire area if used incorrectly a nozzle pressure of 100psi is the standard for fog nozzles

solid stream

fire stream produced from a fixed orifice, smooth bore nozzle. smooth bore nozzles are designed to produce a stream as compact as possible with little shower or spray. a solid stream has the ability to reach areas that other streams might not reach. it can also penetrate and saturate burning materials or debris. characteristics of a solid stream include: -good reach and stream penetration -stream produced at low nozzle pressure -produces less steam conversion -provides less heat absorption per gallon -more likely to conduct electricity (do not use solid streams on energized electrical equipment) the extreme limit at which a solid stream of water can be classified as an effective stream is a matter of judgement. observations and tests covering the effective range of fire streams classify effective streams as: -a stream that does not lose its continuity until it reaches the point where it loses its forward velocity (breakover) and falls into showers of spray that are easily blown away. -a stream that is cohesive enough to maintain its original shape and attain the required height even in a light, gentle wind a nozzle pressure (NP) of 50psi will produce fire streams from smooth bore nozzles with good reach and volume. if greater reach and volume are needed, the nozzle pressure may be increased to 65psi. above this pressure, the nozzle and hose line will require more personnel to handle safely.

broken stream

fire stream that has been broken into coarsely divided water droplets by specialized nozzles such as cellar nozzles, piercing nozzles, and chimney nozzles. while a solid stream may become a broken stream past the breakover point, a true broken stream takes on that form as it leaves the discharge device. in some cases, the effects of a broken stream can be produced by deflecting solid or straight streams off a wall or ceiling so they break up over a fire. broken streams have the following characteristics: -coarse droplets absorb more heat per gallon than a solid stream -they have a greater reach and penetration than a fog stream -they can be effective on fires in confined spaces -may have sufficient continuity to conduct electricity -stream may not reach some fires

how foam is generated

foam concentrate and water are mixed in the correct proportion or ratio with a foam proportioner to produce foam solution. air is then added to the solution through mechanical agitation, or aeration, to produce the finished foam. proper aeration produces uniform-sized bubbles that provide a longer-lasting blanket. a good foam blanket is required to maintain an effective cover for the period of time required for extinguishment

Film Forming Fluoroprotein (FFFP)

foam concentrate that combines the qualities of fluoroprotein foam with those of aqueous film forming foam

apparatus mounted proportioners

foam proportioning systems are often mounted on structural, industrial, wild land and aircraft rescue and fire fighting apparatus

class A foam

foams designed specifically for class A fuels (ordinary combustibles) are increasingly used in both wild land and structural fire fighting. class A foam is a special formulation of hydrocarbon-based surfactants. these surfactants reduce the surface tension of water in the foam solution, allowing better water penetration into the fuel, thereby increasing its effectiveness. aerated class A foam coats and insulates fuels, preventing pyrolysis and ignition from an adjacent fire

water hammer

force created by the rapid deceleration of water causing a violent increase in pressure that can be powerful enough to rupture piping or damage fixtures.

nozzle control valves - rotary control valve

found only on rotary control fog nozzles. they consist of an exterior barrel guided by a screw that moves the exterior barrel forward or backward, rotating around an interior barrel. rotary control valves control the discharge pattern of the stream.

principles of friction loss

friction loss is that part of total water pressure that is lost while forcing water through pipes, fittings, fire hose, and adapters. there is a practical limit to the velocity or speed at which water can travel through a hose line. if the velocity is increased beyond this limit, the friction becomes so great that the water in the hose line is agitated by resistance. in general, the smaller the hose diameter and the longer the hose lay, the higher the friction loss at a given pressure and flow rate. friction loss in fire hose is increased by: -rough lining in fire hose -damaged hose couplings -sharp bends in a hose -number of adapters -length of hose lay -hose diameter friction loss is overcome by increasing the hose size, adding additional parallel hoselines or increasing the pump pressure

fire stream patterns - type

in general, the pattern must be compact enough for the majority of the water to reach the burning material. effective fire streams must meet or exceed the critical flow rate. the major types of stream patterns are solid, fog and broken. all fire streams must have an agent (water), a pressurizing device (pump), a means for the agent to reach the discharge device (hose line), and a discharge device (nozzle).

fog nozzles

may be manually or automatically adjusted resulting in straight stream, narrow-angle fog, and wide-angle fog patterns. characteristics of fog nozzles are: -the discharge pattern can be adjusted -fog nozzles can provide protection to FFs with a wide fog pattern -can be used to apply certain types of foam

compressed air foam systems (CAFS)

mounted on many types of firefighting apparatus. a CAFS functions as follows: -a standard centrifugal pump supplies the water -a direct injection foam-proportioning system mixes foam solution with the water on the discharge side of the pump -an onboard air compressor adds air to the mix before it is discharged from the apparatus. unlike the other foam systems, with CAFS the hose line contains the finished foam

specific application foams

numerous types of foams are available for specific applications according to their properties and performance. some are thick and viscous and form a tough, heat-resistant blanket over burning liquid surfaces; others are thinner and spread more rapidly. specialized foams are used for acid spills, pesticide fires, confined or enclosed space fires and deep-seated class A fires

premixing

one of the more commonly used methods of proportioning. remeasured portions of water and foam concentrate are mixed in a container

pressure loss or gain

pressure loss is caused by friction that is created as the water travels through the hose and by elevation if the nozzle is higher than the pumper. pressure gain will occur when the nozzle is lower than the elevation of the pumper.

medium- and high-expansion foam generating devices

produce a foam that is semi-stable with high air content. there are two basic types of medium and high expansion foam generators: -water-aspirating type nozzle: very similar to the other foam-producing nozzles except it is much larger and longer. the back of the nozzle is open to allow air flow. the foam solution is pumped through the nozzle in a fine spray that mixes with air to form moderate expansion foam -mechanical blower generator: a mechanical blower that is similar in appearance to a smoke ejector. it operates on the same principle as the water-aspirating nozzle except that a powered fan is used to force air through the foam spray instead of water movement. its use is limited to high-expansion foam

foam expansion

refers to the increase in volume of a foam solution when it is aerated. there are three classifications of foam based on their foam expansion ratio: -low-expansion (20-to-1 ratio): effective for controlling and extinguishing most class B fires, and cooling and penetrating class A fires -medium-expansion (200-to-1): used to suppress vapors from hazardous materials spills when applied at expansion ratios of 30-to-1 and 55-to-1 -high expansion (200-to-1 to 1000-to-1): used in confined spaces such as shipboard compartments, basements, mines and enclosed aircraft hangers

fire stream patterns - size

refers to the volume or quantity of water flowing from the nozzle per minute. fire streams are classified into one of three sizes: low volume, handline and master streams. -low-volume stream: discharges less than 40gpm. typically supplied by 3/4in,1in or 1.5in hoselines -handline streams: supplied by 1.5-3in hose, with flows from 40 to 350gpm. nozzles with flows in excess of 350 gpm are not recommended for hand lines -master stream: discharges more than 350gpm and is fed by one or more 2.5 or 3in hoselines or large-diameter hoselines connected to a master stream nozzle. nozzle pressures of 80 to 100psi are common with master stream devices. master streams are large volume fire streams created by master stream appliances such as apparatus mounted deck pipes and ladder pipes. to be effective, a fire stream must deliver a volume of water sufficient to absorb heat faster than the fire generates it. if the heat-absorbing capabilities of a fire stream does not exceed the heat output from a fire, extinguishing the fire by cooling is impossible.

straight stream

semi-solid stream that is produced by a fog nozzle

maintaining nozzles

should be inspected after each use and at least annually. nozzles should be stored with the valve bale in the closed position. use the flush setting on fog nozzles to remove any internal debris.

batch-mixing

simplest method of mixing foam concentrate and water. it is commonly used to mix foam within a fire apparatus water tank or a portable water tank. batch mixing is common with class A foam but less so with class B foams.

foam delivery devices - handline nozzles

smooth bore and fog handline nozzles generally flow less than 350gpm. most handline foam nozzles flow considerably less than that amount -smooth bore nozzles: use is limited to certain types of class A foam applications. in these applications, the smooth bore nozzle provides an effective fire stream with maximum reach capabilities. they are most often used with the CAFS -fog nozzles: can be used with foam solutions to produce a low-expansion, short-lasting foam. these nozzles break the foam solution into tiny droplets and use the agitation of water droplets moving through the air to achieve foaming action -air-aspirating foam nozzles: the most effective appliance for the generation of low-expansion foam. it inducts air into the foam using the Venturi principle.

Aqueous Film Forming Foam (AFFF)

synthetic foam concentrate that, when combined with water, can form a complete vapor barrier over fuel spills and fires and is a highly effective extinguishing and blanketing agent on hydrocarbon fuels

foam proportioning

term used to describe the mixing of water with foam concentrates to form a soap solution. there are four basic methods by which foam may be proportioned: eduction, injection, batch mixing, and premixing

latent heat of vaporization

the amount of heat required to convert unit mass of a liquid into a vapor without a temperature change. for example, when water is heated to its boiling point of 212F additional energy is required to change it from liquid phase to gas phase, but the temperature of water remains at 212F.

nozzle control valves - slide valve

the cylindrical slide valve control seats a movable cylinder against a shaped cone to turn off the flow of water. as the handle is pulled back, the cylinder slides open permitting water to flow through the nozzle without creating turbulence

elevation loss or gain

the difference in elevation between the nozzle and the pumping apparatus causes elevation pressure. changes in pressure caused by gravity must be compensated for by adjusting the pressure at the pump

eduction

the eduction (induction) method of proportioning foam uses the pressure energy in the stream of water to induct (draft) foam concentrate into the fire stream. this is achieved by passing a stream of water through an educator, a device that depends on the Venturi principle to draw the foam through a hose connected to the foam concentrate container and into the water stream

foam hazards

the effect of the finished foam after it has been applied to a liquid fuel fire or spill is a primary environmental concern. the decomposition process results in the consumption of oxygen and the subsequent reduce in oxygen can kill fish and other aquatic creatures. FFs should take care to prevent foam from directly entering bodies of water

critical flow rate

the minimum flow rate at which extinguishment can be achieved

operating fog nozzles

the nozzle reaction will depend on the setting of the fog nozzle. as the fog pattern widens, the reaction decreases, making the nozzle easier to handle.

extinguishing properties of water - vaporization

the primary way that water extinguishes a fire is by absorbing heat which creates a cooling effect. when heated to its boiling point, water absorbs heat and converts into water vapor in a process called vaporization. energy is required both to raise the temperature of water and to change its state from a liquid to a gas (steam). specific heat is the energy needed to increase the temperature of a substance by one degree. in the US this would be expressed in terms of the Btus required to raise the temperature of one pound of water by 1F.

proportioners, delivery devices and generating systems

the proportioner and delivery device/system must be compatible to produce usable foam. foam proportioning simply introduces the appropriate amount of foam concentrate into the water to form a foam solution. a foam-generating system/nozzle adds the air into foam solutions to produce finished foam.

portable foam proportioners

the simplest and most common foam proportioning devices in use today. there are two main types: -in-line foam eductors: designed to be directly attached to the pump panel discharge outlet or connected at some point in the hose lay. using the venturi principle, a pickup tube submerged in the foam concentrate draws the concentrate into the water stream, creating a foam/water solution. the foam concentrate inlet to the eductor should not be more than 6ft above the liquid surface of the foam concentrate -foam nozzle eductors: operates on the same principle as the in-line eductor; however, it is built into the nozzle rather than into the hoseline. as a result, this requires the foam concentrate to be available where the nozzle is operated which can cause logistical problems.

foam application techniques

the techniques for applying class B foam to a liquid fuel fire or spill include the following: -roll-on method: directs the foam stream on the ground near the front edge of a burning liquid spill. the foam then rolls across the surface of the fuel. this method is used only on a pool of ignited or unignited liquid fuel on the open ground. -bank-down method: may be employed when an elevated object is near or within the area of a burning pool of liquid or an unignited liquid spill. used primarily on on fires contained in diked pools around storage tanks and fires involving spills around damaged or overturned transport vehicles -rain-down method: used when the other two methods are not feasible because of the size of the spill area or the lack of an object from which to bank the foam

fire stream limiting factors

there are five factors that affect the reach of a stream: -gravity -water velocity: effective forward velocity of the fire stream ranges from 60 to 120ft per second. this velocity is generated by pressures of 25 to 100psi -fire stream pattern -water droplet friction with air: air friction has a greater effect on the multiple finely-formed water droplets in a fog stream than it does on the outer surfaces of a compact solid stream -wind under ideal circumstances (in the lab), the greatest horizontal reach for a fire stream is attained at 45 degrees from the horizontal plane. in actual operations, fire stream angles between 30 and 34 degrees provide the maximum effective horizontal reach

foam proportioners

there are three types of foam proportioning systems currently in use: portable, apparatus-mounted, or compressed air foam systems (CAFS)

foam concentrates

to be effective, foam concentrates must match the fuel to which they are being applied.

class B foam

used to prevent the ignition of or to extinguish fires involving flammable and combustible liquids. it is also used to suppress vapors from unignited spills of these liquids. the types of liquid fuels that class B foam are effective on are as follows: -hydrocarbon fuels: petroleum based combustible or flammable liquids that float on water, including crude oil, fuel oil, gasoline and others -polar solvents: flammable liquids that mix readily with water including alcohols, acetone and others class B foam concentrates are either manufactured from either a synthetic or protein base. protein-based foams are derived from animal protein. synthetic foam is made from a mixture of fluorosurfactants. foams such as aqueous film forming foam (AFFF) and film forming fluoroprotein foam (FFFP) may be applied either with fog nozzles or with air-aspirating foam nozzles. the minimum amount of foam solution that must be applied, referred to as the rate of application, for class B foam varies depending on any of several variables. unignited spills create vapor hazards that may ignite. a foam blanket can be supplied to suppress the vapors, separating the fuel from the oxygen. once foam application has started, it should continue uninterrupted until extinguishment is complete.

injection

uses an external pump or head pressure to force foam concentrate into the fire stream at the correct ratio for the water flow.

nozzle control valves - ball valve

valve having a ball-shaped internal component with a hole through its center that permits water to flow through when aligned with the waterway. it is the most common nozzle control valve. provides effective nozzle control with a minimum of effort.

operating smooth bore nozzles

when water flows from a smooth bore nozzle it creates force in the direction of the stream and equal force in the opposite direction. the force in the opposite direction pushes back on the nozzle operator in what is called nozzle reaction. one person can usually operate a smooth bore nozzle on a 1.5in or smaller hose line. 1.75in and larger hoselines require additional personnel to overcome the reaction and maneuver the hoseline

properties of steam

when water is vaporized into steam it expands. at 212F water expands ~1700 times its original volume when it turns to steam. when the temperature increases, steam continues to expand. the volume of steam produced depends on the amount of water that is applied. in order for complete vaporization to occur, boiling temperatures must be maintained long enough for the entire volume of water to be vaporized. a solid stream of water has a smaller surface area and absorbs heat less efficiently. when the water is broken into small particles or droplets, such as the discharge pattern that a fog nozzle produces, it absorbs heat and converts to steam more rapidly than it would in a compact form. this occurs because more of the water's surface is exposed to the heat. *the efficiency with which a fire stream absorbs heat is largely dependent upon the surface area of the water introduced into the heated environment or onto the fuel surface. steam production during fire fighting is necessary for effective and efficient use of water as an extinguishing agent. however, care must be taken to apply the appropriate amount of water in the right place to achieve the desired effect. when steam is produced on contact with hot surfaces such as burning fuel or walls and ceiling materials that are hotter than 212F, water is vaporized into steam which adds to the total volume of the upper layer of hot smoke and fire gases. as this total volume increases and the room fills with the mixture of hot smoke and steam, the upper layer of smoke expands downward, potentially making conditions uncomfortable or even dangerous for FFs inside the room. when water turns to steam in the upper layer of hot smoke and fire gases, the upper layer tends to shrink rather than expand. cooling the upper layer requires vaporizing the water while it passes through the hot gases. as the water vaporizes, the hot gases are cooled and the upper layer contracts. because the energy required to heat and vaporize water is much greater than that required to cool the hot gases, the temperature of the hot gases drops faster and farther than the temperature of the steam rises.

fire fighting foam

works by forming a blanket of foam on the surface of burning fuels - both liquid and solid. fire fighting foam extinguishes and/or prevents ignition in several ways: -separating: creates a barrier between the fuel and fire -cooling: lowers the temp of the fuel and adjacent surfaces -smothering: prevents air from reaching the fuel and mixing with the vapors and prevents the release of flammable vapors reducing the possibility of ignition or reignition. -penetrating: lowers the surface tension of water and allows it to penetrate fires in class A materials the majority of fire fighting foams are either class A foams intended for use on ordinary combustibles (class A fuels), or class B foams intended for use on flammable liquids. class B foam is especially effective on the two basic categories of flammable liquids: hydrocarbon fuels and polar solvents