Fire Bridge = Bridge between Plans & Ops


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On the bottom of this POST is WAE’s PDF on Fire Nomogram Use with the Wildland Apparatus Engineers Q-Ref. This is in fact describing what FireBridge is. A mathematical bridging of the FBAN’s estimates to the Operations resources.


THIS Document Is now Translated into SPANISH,   ITALIAN & FRENCH.   Links also on the Bottom of Page.

Some of the formatting might be off a tad, WAE hopes this does not distract to much from the Content. 

The FireBridge concept is what I first began working on several years ago(around 2017 & 2018). This is a concept that takes existing fire behavior numbers such as Rate of Spread and BTU’s and then looks at available resources and tries to bridge the gap so we can apply the right resource with the right amount of suppression. (Think of a Major Life size Nozzle in the Air, we are wanting to create a continuous stream, not just a single drop, then load and return).  I have had folks tell me that we do this already. I challenge that statement because the numbers do NOT add up. Also, the concept of FireBridge is able to be used with any nozzle, engine, SEAT, Helicopter LAT or VLAT because it is not based upon a particular aircraft of engine, it is based all on BTU, i.e. Thermal Exchange.  

Before I begin, let me say that there is one thing that is Never Taught in any of the NWCG courses to date, consisting of standard wildland fire fighter training from S130, S134, S131, S211, S215, S236, S190, S290, S390, S490, PMS-419, PMS-484, and PMS-424. That is  they teach nothing on Fire BTU Generation vs BTU Absorption relationships or how to size it up! 

This is a video of exactly what I am speaking of. The difference is the fuel type, fire ROS, fire BTU/Ft^2 (Called heat per unit area, HPA), and the Q-Ref (WAE’s Quick Reference Book), just tells you how to determine what you need and the coverage area estimations.   The video centers on the Port de Bouc Fire in southeastern France in 2017.

What I am referring to is how to calculate what type and number of air resources you need based on the Fire Nomograms originally produced off the mathematical model originated by Richard Rothermel. Here in his 48 page Report, Rothermel_int_rp115.   from  this 1972 Research Paper INT-115,  he specifically states the purpose of the model and its purpose is for predicting the Fire Rate of Spread and its intensity. That is it. There is NOTHING else on what to do AFTER you have determined the fire intensity and rate of spread as it would relate to the suppression side.  

Rothermels report INT-115, on page 34 speaks of the Application to the Field as it pertains in Item 1. from page 34 which states. “The “hypothetical fire” situation in which operations’ research techniques are utilized for fire planning, fire training and fuel appraisal. 

The snapshot of the PDF page 34 is presented here:

Richard Rothermel goes on to write that each of the fuel models has its own complete set of inputs.  He stated that “on the spot sampling of all input parameters is costly, time consuming and tedious”. Thus cataloging fuel properties and relating them to observable site characteristics does not eliminate the sampling process, but will permit a wide application of sampling results. And he further states that these results can be further refined for use in the mathematical model by assembling them into fuel models that represent typical field situations.  hence the Fire Behavior Nomograms developed and is discussed in his INT-131 Report.  Rothermel_int_gtr131.


Again, FireBridge uses these elements these experts have already put together. All WAE does is complete the other side of the equation.




Bit of History:

All of the data for fire modeling was started as far back as 1946 with Fons, then progressed upward from there.  Concerning fire modeling, such as determining Rates of Spread,  the Heat per Unit Area, Flame lengths, BTU/F/Second, etc. you’ll need to keep in mind, Fire modeling had NOTHING to do with suppression at first, it had to deal with fire being Weaponized!

Suppression was nowhere on their minds(according to the conclusion of the Technical Reports).  I also have not developed any of the prior data. What I do try to do, however, is take existing DATA along with having an understanding of the BTU absorption capacity of water and try to determine how to make things more efficient than they are NOW!  I would also caution and remind all who read this, that NOT A SINGLE technical report to which I’ve read, ever discusses the notion of any suppression efforts or activities. In fact in Charles W. George and Ronald S. Susott’s Research Paper INT-90 of 1971 on pg 5, it states the following concerning retardant …..sic “As the chemical percent is increased, there is a lowering of the pyrolysis and combustion threshold temperature”

Pyrolysis = Decomposition brought about by HIGH TEMPERATURES, usually without oxygen so they won’t combust, however,  combustible gasses are given off. (Pending who’s reports you read see above link from USDA).

Combustion = (basic term) The process of burning something. Usually a reaction between substances including oxygen and usually accompanied by heat and light.

Discussion Point:

So if the 1971 technical report says that Ammonium Phosphate and Sulfate with high percentages reduce BOTH the pyrolysis and combustion temperatures, just what’s that equate to?

All of the Research Papers state factually what a Fire is producing in BTU’s and Rates of Spread. All I am doing here is using their existing data and saying that if the fire is producing this much BTU, then this is the amount of cooling you need for it. Delivery methods are YOUR problem!

So how can we relate what is happening on the fire and equate that to our suppression tools on the ground to be more effective with knockdown and suppression? That was the purpose, to try to BRIDGE THE GAP.  As my former coworker Molly would always ask me, “Yes but Joe, how do you bridge the gap so folks in the operations side will understand what the folks on the Planning side are coming up with, in regards to these BTU/s/ft numbers, etc., How do you determine which helicopter or SEAT or Tanker or even Engine is best suited based on the BTU and ROS“?

This led to the following thoughts and theories in this post.


Has this Method been used Before?


In other countries they use the methods all of the  time, however, in the States very little if any, with the exception of the Martin Fire. Having said this, to what degree their calculations may be in other countries is not known.

This method can be best understood by looking at the Martin Fire in Nevada in July of 2018, and then how it was finally suppressed. I first started talking to some folks in our office about how I thought we were not using our air resources very effectively(in terms of how we were making the drops). The point of my statement was that I always thought we could be much more effective than we currently were. And, I always thought that we had no real clue of what size and type of aircraft to use other than, “bigger fire must then be a bigger plane”.  With this much BTU you have to cool it, then instantly retard it, then Doze it, and it must be in that order and it must be a completely timed even and timed correctly!  BTU delivered(absorbed)  divided by the BTU generated from the fire gives you the efficiency of your effectiveness. How much Heat absorption capacity does LC95 Alone have? To tell you the truth I have never seen a report on actually how much BTU/lb LC95 retardant can absorb. In fact, there has never been any Btu/lb testing done on retardant to date. (4-21-23).

FireBridge is the Concept of Bridging the fire behavior calculations of Heat Per unit Area and Rate of Spread in chains per hour, which then is broken down to determine where the fire will be say 65 minutes or 150 minutes from NOW so that you can plan what size, type and number of aircraft there are to be loaded with water should and at that time?  (For example, a fire with a ROS of 45 Chains per hour, is traveling 2,970 feet in one hour. Or 49.5 feet per minute, or .825 Feet per Second.)

Can the aircraft in the numbers you need be ordered and on location in the allotted time frame? Will you have to delay suppression efforts an additional 15 or 20 minutes to get the right number and size of aircraft? Then are your “additional” aircraft ALSO ready and loaded with LC95 to put the CAP over the newly cooled down fuel? Are your crews and dozers close by to instantly go to work the instant the drops are complete? Crews cannot get close to it if it is not cooled down enough.  In regards to the Operations side of knockdown by matching the Heat Absorption Capacity of water to the BTU the fire is generating, must be based upon the Altitude the fire is at for the drop, and the water temperature. The colder the better but 50 degrees is what we model for.


Below is an example of  what the spreadsheet would be displaying based upon the FBAN’s nomogram outputs. 

FireBridge Spreadsheet for a arbitrary fire model.

Determining Size & Number:

Determining the area that a particular size aircraft can handle is based upon its Gallon Capacity in WATER, and the Water Temperature.  This is the difference.  You can actually calculate fairly easily how much water and what type & size aircraft and how many will be needed to make a drop(s) and then you have to have serious planning to determine the timing between aircraft drops with water to the timing of adding retardant to the timing of dozers.

ALL OF THIS REQUIRES WATER and the ability and knowledge on how to MOVE IT.   The faster you can shove water into the plane (requiring larger pumps), the faster it can take off, the faster it reaches the fire. However, a single aircraft carrying only 28,100,000 BTU worth of heat absorption to a fire producing 700,000,000 BTU is NOT going to work…..AT ALL. When you have one aircraft make a drop, then 20 minutes another one, then another 20 minutes another one, etc. This is worthless and a waste of money and time and real estate on large fires. 

When aircraft have both Daily and hourly rates associated with them, thinking a bit differently might not be the only option, rather perhaps a slightly smarter option?

WAE can tell you how much coverage an aircraft could get versus what the gallon capacity is. It is simply a different way to think about attacking the same problem. Yet it requires close coordination and you have to plan.

If we use the Fire Behavior Nomograms and truly take a serious interest in Fire ground Hydraulics to understand [Properties of Water & BTU], this can easily become the new Normal in Fire Fighting.   If anyone has taken the time to Read Rothermel’s reports (and others) and seen what they considered, you might be amazed at what you could achieve.


Wildland Fire is ALL NUMBERS!

Wildland Fires are a numbers game, Period! Fires produce heat, this is a NUMBER. Albeit a large number but nonetheless it is still just a number. Water absorbs heat, a lot of it. This Heat too is a number and it can, given the right amount, absorb the same amount as what the fire is generating. If you work the numbers, you can determine how much water you need, then you simply need to break that volume up into the other separate pieces that can carry and or deliver it.  

Again, Fire generates heat in the form of BTU and it is measured in Btu/lb of the substance. Water consequently absorbs heat in a equal unit of Btu per pound, BTU/lb. Match these two sets and fire is out. That is FireBridge in a nutshell. It tells you how much water you need.

Think of it this way. If an aircraft drops 3,000 gallons of water in a single instant, then think of that instant as 3,000 gallons in a second. So now that 3,000 GPS = 28,100,000 BTU worth of heat absorption, per second. If the fire you are on is producing less than what was dropped, then the fire is smothered and being cooled now. If not, then it will still be going but may have lost intensity.


This described above method or concept was used in July 2018 on the Martin Fire (link here).

The Fire Behavior Nomograms found here:


Meat & Potatoes:

To give a visual and an update, this is how WAE envisions a better way to use Aerial Resources. First, obtain the fire behavior numbers from Your FBAN or LTAN using the NOMOGRAMS. (PMS-436-3)

For illustration & explanatory purposes, we’re using Fuel Model 13, Heavy Logging Slash, is chosen. However, let us first display from Rothermels General Technical Report #143 from 1983 on how the Nomogram information flow is presented. In RED I have added my perspective to the existing Flow Chart. (Below)


What we see is the left side comprising of all of the Inputs that comprise the “Fuel Model”. Then on the right side you have the outputs that would provide you with the Fire-line Intensity, which, is the Btu/Foot/Second. You would then have the heat per unit area, which is the BTU/Square Foot and then you would have the Rate of Spread and you would be given the Flame Lengths. To clarity, the HPA multiplied by the ROS is the Btu/foot/second. 


Discussion Point:

To the right of this, you can see the term “Suppression Possibility”.  Then nothing else!

In this case, if we know the Rate of Spread and the BTU per Square foot, then the ROS would allow us to determine a couple of things. First, we could determine where the fire will be in say 1hr 50min from now and see if that provides us with a good topographical features to make an offensive Aerial Attack with MULTIPLE Aircraft, or will the terrain be more favorable to the fire?, one will have to determine that for themselves! Second, is if we know the fire dimensions, such as length and width, as well as the fuel loading BTU, we can then determine the total BTU count of the fire and then size up the appropriate type and number of resources.

Figuring out Resources:

To determine the amount of water needed to cool  & “Knock it down”, we have to know two things. The altitude of the fire and the Water Temperature we’re going to use.  I default to 5,000ft Alt and 50 Deg F of water temp.  This provides for a BTU Thermal Absorption Capacity of Water of 1,123 BTU/lb of water. (8.34lbs per gallon times the number of gallons)  A type 1 Tanker carrying 3,000 gallons of water = 25,020lbs, which, if we multiplied this by the 1,123BTU/lb of (which is what each single 3,000 gallon load contains, 28,097,460BTU worth), we end up with 3 Aircraft being required with a BTU absorption capacity of  = 84,292,380.  More than enough for Knockdown.  Next phase is to drop the LC95 right on top of the water drop to place a cap of burn inhibitor on it.  Next you have your ground Crews, Engines, Dozers, etc. move in once the initial wall of heat is knocked down.

Determining the Water Requirement:

If we further take this 71,760,000.00 BTU and Divide it by the 1,123(thermal capacity of each pound of water for altitude) like so 71,760,000.00/1,123 = 63,900.26 Lbs of water are required. 63,900.26lbs/8.34 lbs/gal = 7,661 Gallons. 7,661/3,000 = 3 Type 1 Fixed wing tankers.  

This is where the Aircraft Data section in my Q-Ref comes in handy as it will save you a lot of time doing the math.

Efficiency in the Drops:

Since an aircraft cannot drop 100% of its load on target and be 100% accurate 100% of the time, I’d use a multiplier of say .8 or .9 for 80-90% efficiency and add an additional aircraft or you could simply calculate out the total gallons and simply go up the next largest capacity.  However,  here’s how this mathematically breaks down.

The Nomogram!  

In our model(for illustration purposes only), we simply chose a slope of 20%, and a 10mph 20ft wind speed.  Our Effective Midflame wind speed was simply left at 10mph.

The Green Line represents a Dead Moisture of 4%, mid flame winds 10mph, slope 10%. The HPA shown is about 3,600. and BTU/F/s is about 3,036. But what if it was at 4,600 HPA as in the Redline?

(Yes red line does not hit the moisture dampening curve, this again is only to show a point on how to use the nomogram with our Aircraft Data section in the Q-Ref and what its intended use was for.  WAE wanted to use an HPA of 4,600BTU/ft^2. So the nomogram in this illustration is not intended to be accurate, it’s just a visual).


Sidetracking for just a moment. Using the “actual” 4% fuel moisture would have given us the following:

  1. About 3,500 – 3,600 HPA
  2. ROS of about 45 – 46 Ch/Hr
  3. Approx 3,036 BTU/S/Ft
  4. FL of approx 18Ft


Move down to the 10mph wind speed turn line. then move left to the turn line and then up to the upper left at 4% then over right to the point the lines intersect.

IN this example, we have a ROS of about 51 Chains per hour. A HPA of 4,600 BTU per square foot, a Fire Intensity of about 4,301 BTU/Sec/Ft, and Flame lengths of about 21 feet.

Instead of guessing about BTU/S/Ft. I like to use the ROS figure and divide that out, then multiply the HPA by the ROS in Ft/sec to get the BTU/S/Ft.  To each their own, however, the real reason I do it is to add that extra little “double-check” on the estimation. in this case, the 4,301 BTU/S/Ft seems to fit pretty accurately in the Nomogram space for 51ch/hr.

So to close out,  I’d again have to say that this will require multiple aircraft all in the air, lined up, and each aircraft ready to drop in succession. WATER FIRST, COOL IT then you have your Retardant Aircraft lined up and they drop, Retard It. However, to be effective you don’t want to be waiting a half-hour or hour between each drop. This is a one after the other sortie.

Another thing to think about is if you have Dozers, Engines &  Crews, get them closer to the site so they can instantly go to work after the retardant drops.  This is a Timed Event.

Lastly, we showed above in the flow chart that if you had the Fire BTU calculated and wanted to know the required number of aircraft, you simply divided by the HAC or Heat Absorption Capacity. This is calculated in this manner.

  1. Fire BTU is 71,760,000 BTU
  2. The HAC for each plane selected is 28, 100,000(Rounded)
  3. 71,760,000/28,100,000 = 2.554, so you can either round up to 3 aircraft or try to figure out that third aircraft by taking .554 (the decimal part) x 3,000 gallons to figure out what your next size should be. by the way .554 x 3,000 gallons is 1,662 gallons.  Page 26 & 27 in the Q-Ref can help in your selection.


Ground Coverage Area in Square Feet:

Another thing useful with the Nomograms is that you can then relatively easily determine what the effective area of each aircraft will be.

Back to our Nomogram for above, if our HPA, as shown above, is 4,600 BTU/FT^2, and we know that our Type 1 Tanker holds 3,000 Gallons with 28,100,000  BTU of absorption (if all water), then we simply take the 28,100,000/4,600 = 6,108 Square Feet of coverage (at best). This is where I was saying you might want to add that .8 multiplier to factor for losses and add aircraft.

6108 x .8 = 4,886 Square feet and we’d now need  from our original fire square footage of 15,840 / 4886 = 3.2 Aircraft.

I would not jump and say, “might as well make it 4” either,  remember, the .8 is chosen arbitrarily to illustrate a point that regardless of how good a pilot is, you can’t be 100% precise all the time. A .9 multiplier (for 90%) might suffice just fine as well. It’s the best estimation.

There will be a link in the store section soon that will explain more on how to use the Nomograms with the Wildland Apparatus Engineers Q-Ref, this is FireBridge:


Fire Nomogram Use with Wildland Engineers QRef4 – English

Remember, Engineers, Make it Happen! 

The Spanish Translation: FireNomogramUsewithWildlandEngineersQRef4-es


The Italian Translation: FireNomogramUsewithWildlandEngineersQRef4-it (1)

FireNomogramUsewithWildlandEngineersQRef4-it (1)

The French Translation: FireNomogramUsewithWildlandEngineersQRef4-fr


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