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  • Rollover/ thermal layer ?

    Hi everyone! I need to settle an argument. In the rollover stage of a fire, I understand that if I hit the hot gasses with a fog nozzle, the thermal layer will be unbalanced and the chances are we are getting burned by steam. My question is, can I hit those gasses with a straight stream out of a fog nozzle, or does it have to be a solid stream (no fog nozzle)? Thanks for your info!

  • #2
    In firefighting terms - what is Thermal Balance? There appear to be varying definitions in relation to this term but the earliest reference appears in work completed by Keith Royer and Floyd Nelson of Iowa University during the late 1950s.

    The degree of thermal balance existing in a closed room during a fire's development is dependant upon fuel supply and air availability as well as other factors. The hot area over the fire (often termed the fire plume or thermal column) causes the circulation that feeds air to the fire. However, when the ceiling and upper parts of the wall linings become super-heated, circulation slows down until the entire room develops a kind of thermal balance with temperatures distributed uniformly horizontally throughout the compartment. In vertical terms the temperatures continuously increase from bottom to top with the greatest concentration of heat at the highest level.

    John D. Wiseman writes (In the Iowa State Story) that there are several meanings to the term 'thermal balance'. First it means that the energy coming into the fire must equal the energy being released. Keith Royer explains "The amount of air that comes into the fuel is directly proportional to the amount of combustion that goes away from the fuel. So basically what a fire is trying to do is to seek some sort of equilibrium between products getting away and products coming in. Anything that disrupts either flow throws it out of balance".

    Royer further stated that "the importance of maintaining thermal balance in the area of extinguishment is critical. Without thermal balance operations become delayed". He went on to say that "thermal imbalance occurs through turbulent circulation of steam and smoke" in the fire area and this leads to decreased visibility and uncomfortable conditions.

    It has been noted, through monitoring of compartmental temperatures at varying levels, that temperature inversions can result during over zealous use of water in either fog or straight stream (smooth-bore) form. This can lead to temperatures at floor level exceeding those at ceiling level for short periods, creating an extremely uncomfortable environment for firefighters occupying the space. In this state, the compartment could be said to be thermally imbalanced.

    The US Navy referred to thermal balance when reporting on their research into 3D gas-cooling applications as follows -

    "The offensive (3D) fog attack also resulted in the least amount of disturbance to the thermal layer. The disturbances of the thermal balance within the fire compartment were best shown by comparing the total heat flux measured by the calorimeters mounted 0.9 m and 2.4 m (3 ft and 8 ft) above the deck in the fire compartment. The key indicator of significant disturbances in the thermal balance was the upward spike in the 0.9-m (3-ft) heat flux that approached or met the heat flux for the 2.4-m (8-ft) calorimeter. This indicated total compartment mixing with steam.

    During the offensive fog test, the initial attack actually cooled the upper layer enough to result in a 14.2-kW/sq m (1.25 Btu/sq ft-) drop in the 2.4-m (8-ft) heat flux level. While steam was produced, it was described as more of a moist "sweaty" type of steam rather than a hot penetrating steam. In contrast, for the straight-stream test, there were several instances in which the thermal balance was disturbed sufficiently to cause the upward spikes on the 0.9-m (3-ft) heat flux plot (see Figure 3). For all of the straight-stream evolutions, the thermal balance was disturbed sufficiently to impose a serious heat and steam threat to the attack team members. To highlight the significance of this finding, it was noted that none of the attack team members suffered burns during the offensive fog attack tests, whereas many of the straight-stream attacks resulted in burns to the hands, wrists, face, neck, and back".

    http://www.firetactics.com/THERMAL%20BALANCE.htm
    Euro Firefighter 2008 - Strategy & Tactics from the World's Firegrounds

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    • #3
      HTFD~
      Granted this is just my opinion, but, fire fighting is not rocket science. You put the water on the fire and it goes out. You fog into the ceiling and you might (no you probably will) get steam burns. You shoot a quick hit with straight stream (out of a fog nozzle)into the ceiling and it will create enough steam to knock down most content fires. Ive never been burned doing this. Guys that do get burned usually keep the nozzle open too long or aren't low enough.
      In Phoenix we dont even have straight stream nozzles other than our master tips. I know some depts swear by them and i believe those guys. We just never use them ... apples and oranges really.
      try it you'll like it

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      • #4
        Cake&Bowls........'You shoot a quick hit with straight stream (out of a fog nozzle)into the ceiling and it will create enough steam to knock down most content fires. Ive never been burned doing this'.

        I am sorry but this style of firefighting just doesn't make sense? If you are attempting an indirect attack from inside you WILL get burned if the overhead is hot enough. The ONLY reasons a firefighter should apply water into the overhead whilst holding an interior position is to take heat out of the gases; or extinguish an amount of fire gases that are burning off near the ceiling; or to inert a dangerous smoke/gas layer that is forming above your heads. To attempt to extinguish (or knock down) a room & contents fire by creating steam is definitely asking to get burned!

        However, a few brief controlled bursts of the nozzle on a medium 35 degree fog cone will take that heat out and stop the rollover. This 'pulsing' style of attack has been adapted for interior use simply because it does NOT create uncontrolled amounts of steam and cools the overhead more effectively than any straight stream - as so many scientific tests have shown us - as so many firefighters who have used these tactics can tell you. I have the greatest respect for Phoenix as a fire department and I am a little surprised you guys haven't been introduced to 3D water-fog nozzle 'pulsing' for dealing with rollover conditions.
        Euro Firefighter 2008 - Strategy & Tactics from the World's Firegrounds

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        • #5
          Holy Textbook Batman ...

          Every fire I've been in, we've been able to hit the ceiling w/ quick bursts of straight stream from a fog nozzle and it has either a) controlled the rollover so that the SAR crew could complete their search or b) kept the fire from rolling back over us to the point where we could advance on the fire and put it out.

          This is just my experience.

          Stay Safe

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          • #6
            I knew as soon as I saw the title of this one we'd see Paul chime in. He doesn't disappoint.

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            • #7
              I hear you on that Gunny!!!

              PA Volly - I take your point and you are right. The straight stream used in short bursts WILL knock back a rollover as you say although it is proven that a fog pattern used the same way is more effective. I was just making the point....and maybe I read in incorrectly....that Cake (what kinda name is that for a FyreFgtrs forum!) seemed to imply that the entire contents fire was suppressed - that would need a LOT of steam!
              Euro Firefighter 2008 - Strategy & Tactics from the World's Firegrounds

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              • #8
                Yep I knew it wouldn't be long before we heard from Paul either, and although 3d fog attack has some merit in controlled (highly controlled) conditions I don't think it will work as well on a day to day basis. You can hit the thermal layer with a fog(straight stream) and it will usually create enough steam to prevent a flashover, sometimes, not always. There are several problems with this, too wide of an angle, too much or not enough gpm, etc.Remember the situation is not constant, it is dynamic. The biggest danger in using a fog is probably that you will bring the steam down obscuring vision and injuring potential victims. (dry heat is still better than wet heat). You can also use a smooth bore and do the same thing by bouncing the stream off of the ceiling. It's conceivable that a well built fog nozzle may disperse it's stream before it gets into the ultra-heated atmosphere, so you still could have some potential for a flashover, where the smooth bore would have a better chance of hitting the ceiling and dispersing in the superheated atmosphere. We have a flashover simulator down here and the fire can be controlled with only 30gpm,(straight stream fog). The biggest problem we have in this controlled environment is making too much steam and putting out the fire and bringing the atmosphere down on ourselves. (it's a very delicate balance)but I can't imagine that you would want to go after a fire with that amount of water. I use a smooth bore that doesn't make as much steam, but has much more reach in a heated atmosphere(maintains it's stream), if I need steam, like I said,I bounce it off of the ceiling. But please remember that there is no perfect nozzle and generally fires aren't fought in a controlled steel box. www.I'mnotbuyingfiretactics.com

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                • #9
                  OK Blacksheep I read your points and almost (almost) found myself agreeing with some of what you say But HEY Lt.!! www.imnotbuyingyourphilosophyeither.com

                  In the flashover cans we have in the UK some guys have been extinguishing the rollovers with flows as low as 12 gpm applied into the burning gas layers at high-pressure off the booster lines! Now don't think for one minute I go along with that! But these 'rollover' simulations are exactly that! I have a job trying to tell these guys that its NOT a reeeeel fire! There's only 20 Cu.metres of fire gases involved and no class 'A' fuel load....no furniture....no wall linings....no contents!

                  I have used 3D fogging techniques repeatedly in REAL fires over a ten year period - and this form of application definitely worked for me.

                  However - you do raise some valid points Lou....

                  If you bring excessive steam down then its because you need more training with the nozzle - thats common when training in the containers and it takes a few evolutions to get to grips with the application techniques.

                  Angles and droplets are easily dealt with by choosing well designed equipment. TFT specially designed a nozzle that enables correct cone patterns to be found in darkness........Akron have adapted 'trigger' operated nozzles that suit 'pulsing' although I am not a big fan of this one. The droplets are optimised with spinning teeth rings or using correct nozzle pressures.....all these things can be pre-set or part of your SOPs. If you are putting the fire out through excess steam it may be that your droplets are too big? If they aren't evaporating in the gases then they are striking surfaces - and the droplets are over-sized. Check the spray pattern in still-air and look for a 4-6 second drop from suspension.

                  Low flows of 30 gpm are ok for gas cooling and if you have a selector ring you can increase your flows when required. If not, you can just crack the flow control to 'pulse' small amounts of water into the overhead.

                  FINAL point - a smooth-bore or straight stream CANNOT inert fire gas layers. I have repeatedly achieved success in placing fine water droplets (suspending them) into smoke and fire gases above our heads.....you know the stuff....thick, black and rolling superheated gases heading for the exit behind you! The suspension of water mist in these gases most certainly can and WILL 'inert' the smoke far more effectively than a straight stream.........possibly preventing or quenching a backdraft or smoke explosion.

                  I never propose this style of application as an alternative but rather an addition to the range of streams we can use in controlling a specific range of conditions.

                  I KNOW you have played with these techniques Lt. and I know you have the opportunity to do so under controlled conditions. If its not working for you then look at your nozzle and droplet range? I can crack a 150 gpm flow on a 35 degree fog with a few brief controlled bursts and take control of the overhead before narrowing down to a straight stream and hitting that fire.

                  In the end - its what works for you - I respect that - do what you know best - what you feel comfortable with. But do try all options.
                  Euro Firefighter 2008 - Strategy & Tactics from the World's Firegrounds

                  Comment


                  • #10
                    HTFD4107

                    can I hit those gasses with a straight stream out of a fog nozzle, or does it have to be a solid stream (no fog nozzle)?

                    Yes, you can hit them with a straight stream from a fog nozzle as long as the fog nozzle will go to straight stream.

                    PA Volunteer

                    Every fire I've been in, we've been able to hit the ceiling w/ quick bursts of straight stream from a fog nozzle...

                    HOLY ELKHARTS!

                    A nor-easterner using a fog nozzle!

                    This is just my experience.

                    And everyone else that uses a nozzle properly shares the same experience.

                    BLACKSHEEP-1

                    It's conceivable that a well built fog nozzle may disperse it's stream before it gets into the ultra-heated atmosphere, so you still could have some potential for a flashover,

                    When and where has anyone with a properly operated nozzle, either solid or fog, been injured in a flashover?

                    where the smooth bore would have a better chance of hitting the ceiling and dispersing in the superheated atmosphere.

                    I have yet to not hear a straight stream from a fog hit the walls and ceiling when being penciled to reduce flashover potential.

                    www.I'mnotbuyingfiretactics.com

                    This link doesn't work

                    [ 01-10-2002: Message edited by: mongofire_99 ]

                    It's only my opinion. I do not speak for any group or organization I belong to or associate with or people I know - especially my employer. If you like it, we can share it, you don't have to give me credit. If you don't, we are allowed to disagree too (but be ready to be challenged, you may be on to something I'm not). That's what makes America great!

                    Comment


                    • #11
                      [quote]Originally posted by mongofire_99:
                      HTFD4107

                      PA Volunteer

                      Every fire I've been in, we've been able to hit the ceiling w/ quick bursts of straight stream from a fog nozzle...

                      HOLY ELKHARTS!

                      A nor-easterner using a fog nozzle!





                      Hey Mongo ... don't worry, I don't like it, I'd much rather have a smooth bore, but it's what we got!

                      Stay Safe

                      Comment


                      • #12
                        Oh, man...

                        [ 01-11-2002: Message edited by: mongofire_99 ]

                        It's only my opinion. I do not speak for any group or organization I belong to or associate with or people I know - especially my employer. If you like it, we can share it, you don't have to give me credit. If you don't, we are allowed to disagree too (but be ready to be challenged, you may be on to something I'm not). That's what makes America great!

                        Comment


                        • #13
                          keep your eyes open for flashovers. If you see this(in time).take your hose and hose you and your partner down in the fire down as much as you can quickly and get the heck out of that fire ,and stay low.

                          Comment


                          • #14
                            From what've I been taught and experienced you don't have much time to hose your self down along with your partner. I would spend that time leaving the room personally. Also I'm lead to believe that would wetting yourself down first would lead to steam burns. Correct me if I am wrong.
                            NREMT-P\ Reserve Volunteer Firefighter\Reserve Police Officer
                            IACOJ Attack

                            Experts built the Titanic, amateurs built the Ark.

                            Comment


                            • #15
                              [quote]Originally posted by Maplewood F.D.:
                              keep your eyes open for flashovers. If you see this(in time).take your hose and hose you and your partner down in the fire down as much as you can quickly and get the heck out of that fire ,and stay low.


                              Excellent way to achieve steam burns.
                              Doc DC3<br />ex FDNY (E74)

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