INTERIOR FIRE ATTACK

INTERIOR FIRE ATTACK

FIRE STREAMS AND ATTACKS

Fire Captain J.T. Terlaje

The hallmark of a good fire department is the ability to make an aggressive interior attack. When occupants await rescue and are trapped by fire, it is the aggressive fire department that will save them. Whenever the topic of interior structural fire attack arises, there is always debate as to which method of fire attack is best. Some departments rely on the direct attack method, while other departments attempt an aggressive interior attack using the indirect or combination method.

Not all fires are alike, and methods of fire attack differ depending on the situation. Fires progress through the three stages; the incipient, the free burning and the smoldering stage. Each stage is characterized by differences in room temperature and atmospheric composition, and each will respond differently when attacked by the various methods, namely the direct method, the indirect method and the combination method. Certain types of fires may best be extinguished using one, two or all three methods of fire attack, while others succumb best to only one particular method. A knowledge of which method best suits a given situation allows a firefighter to perform his duties in the safest and most effective manner.

In addition, the need for effective fire flow goes hand in hand with any fire attack strategy. Efficient fire streams are sometimes taken for granted; the importance of adequate fire flow with manageable nozzle reaction is sometimes overlooked.  All of the fire attack theories have a single underlying foundation: Each is designed to effect extinguishment of a fire. From this point on, each method differs from the others.

WHAT ATTACK TO USE?

DIRECT ATTACK

The direct method of attack is simply applying water to the base of the burning material, at the flame/fuel interface, where the flammable vapors being distilled by heat from solid material ignite and burn. The direct method of attack causes little disruption of the heated combustion products. Reducing heat production by extinguishing the fire at its base stops the burning process at its source, in turn stopping the upward liberation of more heat, smoke, and gases. The direct attack can be used in the incipient and free burning stages of fire.

If ellipse, the officer feels the overhead needs to be cooled because it is pre-venting provide temperature reduction without generating a massive amount of steam. This helps eliminate the threat posed by the heated gases without excessive unwanted steam production and violent disruption of the thermal balance characteristic of the indirect and combination methods."

DIRECT ATTACK ANALYSIS

This attack is designed to extinguish the fire by applying a straight or solid stream at the base of the fire. It offers the greatest penetration of heat being produced and allows greater distance between the nozzle and fire. It is safer to attack the fire from a greater distance than from a closer distance. The stream will then strike the combustibles and cool them below their ignition temperature, thereby effecting extinguishment.

These straight or smooth bore streams will produce less steam, as the water is in a tighter pattern. Producing an excess amount of steam may disrupt the thermal balance in a confined area, forcing the superheated air lower to the ground. Maintaining a thermal balance is a must when performing a direct attack since firefighters are usually lower to the ground where the temperature is lower.

In environments of high heat, the stream should be directed into the overhead for a period of several seconds at a time, in an effort to lower the temperature. Since the danger of flashover is very real in an enclosed area, it is important to recognize this danger and a means of preventing it. Remember that smoke is incomplete combustion; when present with enough heat and oxygen, smoke will ignite with catastrophic consequences. Water properly applied into the overhead provides a safety net and prevents flashover.

INDIRECT ATTACK

In situations where there is no need for an aggressive lifesaving effort in the extinguishment of a structure fire an indirect attack can be used. This technique was pioneered by Chief Lloyd layman of the U.S. Coast Guard Firefighting School for use on open burning shipboard fires. This attack is suitable for fires that are in the third stage of burning (smoldering), because most of the elements for a successful indirect attack are present. The basic requirements for an indirect attack are high heat conditions throughout the area and limited ventilation of the fire area.

As you can see, high heat and limited ventilation are two classic indicators of a third stage fire. Once this has been identified create a very small opening in a window, door or rollup gate and direct a 30° fog pattern through this opening, sweeping the ceiling in a side to side motion. Under these conditions, when water fog is injected into a superheated atmosphere, the water is almost instantly vaporized and turned to steam. In doing so, it absorbs huge quantities of heat from the fire and the surrounding areas,. It also expands in volume. Each gallon of water can expand 1500-2000 gallons of steam when fully vaporized. This steam will rapidly fill the fire area, pushing smoke and heat ahead of it and forming an inert atmosphere even in areas remote from the point of water application. Keep the stream open until the volume of steam being expelled around the nozzle begins to diminish substantially.

If conditions permit, proceed with opening up and then advance using the combination attack method to extinguish any remaining fire. If resources do not permit a rapid follow up and advance of sufficient hose streams for immediate follow up then it is best to leave the area sealed and let the steam soak in. This steam atmosphere must have several minutes of soaking time to have the desired smothering effect. Otherwise, if ventilation is performed prematurely, reignition may occur throughout the superheated area.  

Although this indirect attack method can work in certain circumstances, it isn’t practical for the majority of structure fires for a number o reasons. The first and most important reason is its total unsuitability for use on areas that pose a potential life hazard. The conditions that make it impossible for the fire to exist also makes human survival impossible, this fact along with the soaking required and the subsequent delay in searching for and removing occupants, pose and undue risk to human life. The second reason is the unlikelihood of finding all of the necessary ingredients present simultaneously. As all method of attacks have prerequisites, so too does the indirect attack. The four key requirements are:

·         no occupants

·         limited ventilation

·         high heat

·         limited size of the potential fire area

Although there is a trend to seal buildings, fire has the ability to break through glass, thereby self venting. If you arrive at a building to find smoke or fire venting out several openings, chances are an indirect attack may not be successful. The fire must also be hot enough to expand the fog stream into steam. On the other hand the fire must not be so large as to overwhelm the capabilities of an indirect attack. Large area commercial structures are unlikely locations for this tactic, since the steam generating requirements are greater as the building increases in size.

It is important to recognize that the use of the indirect method of attack alone may not prevent a backdraft explosion. In all potential backdraft situations, the application of water should, if possible be timed to occur after topside ventilation. This will funnel the fire gases into the proper channel, letting the hottest gases out first while the steam follows upward convection currents, extinguishing fire along the way.  

AVANTAGES

The use of the indirect attack method can greatly reduce firefighter’s exposure to potential backdraft situations. Under the proper circumstances, this method can extinguish fires in areas where the heat conditions deny entry to firefighters, such as fires in the holds of ships, railroads cars and shipping containers are often candidates for this method. The indirect attack allows a very limited crew to extinguish more fire than would be possible using the combination attack. It can also extinguish fire in area remote form the point of water application. If a direct or combination were used, the hoseline would have to be advanced to this remote area, usually through the interior, a slower process. In addition, ventilation support isn’t as critical in the indirect attack, so these personnel can be used to press t he attack. It is important to remember, that this is only possible if conditions are right.

Another advantage of the indirect attack is the use of less water for extinguishment. When operating from an apparatus booster tank or in other situations of limited water supply, the efficiency of fog- both to absorb more heat and to produce the blanketing effect of steam can reduce the required volume far below the amount required for a combination attack.

The indirect attack also causes less water damage than the direct and combination attack. When conversion to steam is accomplished most efficiently, nearly all of the water is used for extinguishment, and there is little excess runoff.

DISADVANTAGES

The indirect cannot be used in an occupied building. To do so would concede the loss of any remaining occupants. The resulting atmosphere is untenable even for the firefighter in protective clothing. Just as the steam progresses to remote areas as it extinguishers the fire, so will it affect the people in its path.

The presence of ventilation openings will dilute the effect of the steam. If enough windows or doors have vented prior to water application, no steam buildup is possible. A discharge of less than the critical volume can push fire ahead of the steam, an effect that may not be observed from the outside. Blowing fire into vertical or horizontal voids is particularly dangerous since the fire may be in control of so many voids by the time the situation is recognized that opening them all is impossible.

It isn’t possible to view the interior layout until you have gained control of the situation. Unlike the direct or combination attack method it isn’t possible to get an idea of what the floor plan is like by looking in below the smoke. The members will be operating in very poor visibility once they do enter.

Using the indirect attack may increase water damage if the company uses this tactic in an inappropriate situation, it may result in soaking materials that aren’t threatened by the fire. Fires in mattresses and overstuffed furniture produce tremendous amounts of smoke. If an inexperienced member arrives to find heavy smoke showing from every crack yet fails to evaluate the level of heat, he may begin an indirect attack that is doom to fail. These types of fires don’t normally develop the superheated atmospheres required for successful steam conversion. The member could be operating the stream into a room that isn’t even in the fire area.

COMBINATION ATTACK

Like the indirect method of attack, the combination attack was originally designed primarily for exterior application of water. The objective of the combination attack is to 'roll' the stream around the perimeter of the room, cooling the walls, ceiling, and floor with the outer edge of the stream while the inner portion of the stream cools the hot gases being produced by the fire.

This method of attack most often used in the free burning stage. This initially consists of sweeping the ceiling with the straight stream in a side to side or a clockwise circular motion. This ceiling level attack is only done for  five seconds, just long enough  to cool the hot gases that have built up overhead and preventing it from igniting or a flameover. Then by dropping the stream, you cool the burning materials, causing them to cease production of any further gases and flame. Remember that flame is simply the burning of the gases released by a fuel. Until you cool the fuel sufficiently, it will continue to give off more flammable gases.

COMBINATION ATTACK ANALYSIS

These theories of fire attack were never designed to be used as part of an offensive interior attack. Over the years, mainly through a lack of understanding on the part of many individuals and departments, these theories were misapplied. The combination attack has proven very successful and has the following advantages and disadvantages.

ADVANGATES

By using a straight stream or a very narrow fog to hit the ceiling first, you cool the fire gases nearest the line without creating too much steam, which could obscure your vision or force withdrawal. This process also stops the travel of fire and pushes it back toward its area of origin without causing a buildup of higher pressures in the fire area, which can occur if a wider fog pattern is used. By then dropping the angle of the stream, you cool the burning materials without having to be right on top of them.  To begin a direct attack on a free burning fire would endanger the nozzle team. If the stream were initially directed toward the burning materials, the fire would be driven up and along the ceiling over the hose stream, coming down either on top of or behind the nozzle team or igniting other objects in its path. The combination attack avoids this rollover effect.

By shutting down the line when no fire is visible, you will not disturb the thermal balance too severely within the fire area. Quite often, the ceiling temperatures in a fire room will reach 1200–1500º F while those at the floor are in the range of 125-150º F, a survivable temperature. This tendency for heat to rise can be put to good use if you coordinate ventilating with fire attack. When you have darkened down the fire and if you have shut down the stream, the heat, steam, and smoke will tend to lift a few feet off the floor, improving visibility and allowing the hoseline to advance. It will also allow any remaining hidden fire to light up so that the overhaul team can locate and extinguish it.  The combination attack seeks to avoid disturbing the thermal balance in the event there are people within the fire building – firefighters as well as potential victims. By keeping the heat at the upper levels and the cooler air at the lower levels, the combination attack helps preserve the chances of survival. 

The combination attack puts the firefighters inside the structure near the seat of the fire. They are therefore in the best position to accomplish their primary goal, which is to save human life. Remember that human life is the first order of priority and far outweighs property value. This placement usually puts the hoseline in a position to push the fire back toward its origin or out ventilation openings, which also protects the greatest amount of property as well as life.

DISAVANTAGES

The combination attack puts members within an extremely hostile environment. As soon as firefighters enter an involved building, they are exposed to much greater risks than they might encounter outside the building. When human life is at stake, firefighters must take reasonable risks to save these lives.

The combination attack requires live fire training to develop a high degree of proficiency. Two errors are common in this attack. The first is that the nozzle man forgets to check his stream pattern and opens up on the fire in a wide fog pattern. This can be catastrophic, since the resulting steam can chase the nozzle team out of the enclosed area, possibly resulting in steam burns. In addition, the steam could kill any unprotected occupants, and it could push fire into previously uninvolved areas. This lesson will almost never be forgotten by anyone who experiences it.  

The second error involves leaving the stream un on the ceiling too long without dropping the angle. This doesn’t serve to cool the fuel, with the result that the stream doesn’t seem to be making any progress. All the initial attack on the ceiling is supposed to do is cool the hot gases that are traveling along that area, either flame or extremely hot smoke that contains flickering tongues of fire rollover. As soon as the overhead fire is extinguished the line should go to work on the real source of the overhead gases-the rest of the room. Although the change is visible to the firefighters, sometimes they may not recognize that the line has had its desired effect and that they must now change their angle of attack.

           

NOZZLE REACTION AND FIRE FLOWS

FIRE FLOWS AND NOZZLE REACTIONS

1 ½” handlines, while not as popular as 1 ¾” lines, can flow about 125 gpm efficiently in stretches up to 200 feet. A larger-diameter line must be used to fill out stretches longer than 200 feet-for example, 2 ½” hose to a reducer or a wye followed up by the 1 ½” or 1 ¾”  handline tasked with extinguishment. Simply put, friction loss becomes a major factor in the longer stretches, and pump efficiency and capability then become factors. This is a topic unto itself and will not be fully discussed here.

Although they can deliver flows of up to 185 gallons per minute, most departments are not flowing anywhere near this simply because of the very high nozzle reactions they are encountering. Probably, the most important point to keep in mind is that in the interest of safety and efficiency, a sufficient volume of water must be available through medium-diameter attack handlines. Small-diameter lines of less than 1 ½” are not suitable for interior fire attack operations. Although there is no doubt that many fires can be handled with the limited flows of a one-inch booster line (about 40 gpm), no additional flow will be available if needed.

As important as adequate flow is to fire suppression operations, you must remember that nozzle reaction is the ultimate decider of effective fire flows for handlines. In other words, if the nozzle reaction is significant, the nozzle operator will do one of two things:

If he cannot control the nozzle reaction exhibited by the stream, he will gate down to deliver a lesser flow with more manageable nozzle reaction, or the nozzle operator will simply lose control of the handline and suffer the corresponding deadly consequences.

Nozzle reaction is directly attributed to nozzle pressure and flow (measured in gallons per minute). Realistically, a two- person nozzle team (consisting of a firefighter assigned to the nozzle and a second member in a backup position) can safely and effectively control somewhere between 65 to 70 pounds force of nozzle reaction. The higher the nozzle pressures at a given flow, the greater the nozzle reaction. Note that the lower the nozzle pressure, the less nozzle reaction at a given flow. A lower reaction with a higher flowing handline means greater safety and more water delivered in a shorter time.

Remember that to extinguish any given Class A fire requires that you deliver the flow rate needed to absorb the given Btus. If the volume of water needed is not delivered, the fire will continue to grow until it consumes all the given combustibles within its reach. As the fire eventually burns itself out, the Btus given off will be absorbed by the flow rate being delivered, and the fire will be extinguished. As an example, if a fire requires a flow rate of 200 gallons per minute for extinguishment and only 40 gpm are  delivered, the fire will not go out. It will continue to burn until the Btus given off are low enough to be absorbed by the 40-gpm flow rate.

This is simply a matter of physics and cannot be changed. How then can we deliver a flow sufficient to accomplish rapid extinguishment without endangering ourselves? Ultimately, we want to deliver as great a flow as possible in the shortest period of time and in the safest and most effective manner. To do this, we must strive for high flows with limited nozzle reactions and consistent application of the fire stream in a safe manner.

What flows are considered best for our medium-diameter handlines? As a rule, the more water a suppression team has available, the more fire it can extinguish and the safer the incident will be. How much water to flow should be based on the consideration of how much nozzle reaction you can safely handle. If your nozzle team can control the line safely up to 65 to 70 pounds of force reaction, base the flow volume on that value. Even if nozzle reaction is held to a manageable level, it is still imperative that a firefighter be assigned to the backup position. Although not the most glamorous position, it is a most critical one. The backup person is responsible for absorbing the great majority of the reaction, which allows an adequate amount of water to be delivered. Without the backup person, the attack becomes less efficient and safety is compromised. Obviously, the more members assigned to the stretch, the more efficient and safer the fire attack.

WATER DAMAGE

Water damage is not caused by flow rate but by prolonged application of water by an untrained nozzle team that does not know when to shut off the line. A stream flowing 60 gpm for 25 minutes will cause more water damage than a stream flowing 200 gpm for one minute. An effective nozzle team knows when to open and shut down a line and what stream patterns and techniques to use.

VENTILATION

Ventilation is paramount to any interior attack. Even though it is not the theme of this presentation, it must be included. Combustible gases are inherently dangerous and await only a sufficient amount of heat and oxygen to ignite. It is imperative that the products of combustion be allowed to exit. For the members inside making their attack, these combustible gases are better off outside the building than inside with them. Sometimes, ventilation is not easy to accomplish. When this happens, the threat of flashover is very real, and getting water into the hot gases will delay or eliminate this threat.

Direct attack advocates say that it is important to get a stream into the overhead area when there is intense heat even though no fire has been encountered. A stream into the overhead for a period of several seconds will delay flashover while the advance to the seat of the fire continues. Flashover mitigation and fire extinguishment can take place with the indirect and combination attack, but these methods were never designed for inside application when victims or firefighters are present. Again, the massive generation of steam would cause extreme problems for those inside.

CONCLUSIONS

With regard to fire suppression strategies for interior firefighting, the biggest conclusion that can be drawn is that the generation of steam within a confined area can prove detrimental and dangerous to all inside the structure. The original theories of the indirect and combination methods made it very clear that massive amounts of steam had to be generated. In addition, the techniques used in the combination attack  water fog approach also make it very clear that too much steam will have negative consequences. Water dispersed in a fog (spray) pattern will turn to steam more quickly than water confined within a straight stream. This rapid expansion in a very high heat environment can cause injuries.

Another conclusion drawn from the various forms of attack is that the wide fog pattern used in all but the short "pulses" can push fire and heat into uninvolved areas. Ultimately, the data available show that the direct method, which relies on the straight (or solid) stream, is the most effective pattern for fire extinguishment.  The combination attack  water fog strategy also relies on the direct attack method, but, as stated, using a fog pattern in short applications renders the approach safe. Overuse of water, regardless of the pattern used, can inhibit the attack by creating excess steam and disrupting the thermal balance. Another clear fact that emerged is that more water can be safely delivered at a lower nozzle pressure simply because you will have to contend with less nozzle reaction. The fog nozzle vs. smooth bore nozzle debate has been covered extensively in other articles.