By Kristofer M. DeMauro
Early in my firefighting career, I worked with a captain who taught me more about firefighting than anyone else. He taught on the tailboard, around the table, and even on the way back from calls. As a matter of fact I cannot remember him ever teaching a formal class. A lesson that stands out in my mind and one that I use every day on the job came from a simple question that I posed, “Cap, I know about strategies, tactics, incident command, and all of the stuff I am required to know, but how do you put it all together? How does it work?”
His reply was simple, direct, and exactly what I needed to know: “Well, it is an easy equation to figure out as long as you know all of the factors.” He took out a blank incident run report, turned it over to the blank side, and began to draw out a diagram. “You know the fire triangle, don’t you?” (I’m dating myself here.) “Well, we are going move on up to a square.”
The Thompson Diagram, named after Assistant Chief Lowell Thompson (then Captain Thompson), is based on four interconnected needs that a fire officer must consider when sizing up and attacking a fire. These needs are:
- Needed fire flow
- Staffing
- Water supply
- Application rate
These needs will be different for every fire, because no two fires are exactly the same.
Chief Thompson drew a square on the paper and assigned a “need” to each side. I kept the drawing for a long time, and wish that I still had it. There was a reason for the placement of each need on the outside of the square. Slowly and methodically, he explained to me how it all worked. When he was done, I had a light-bulb moment in which it all clicked and made sense to me. For the first time I felt that I could do this job; I might even be halfway good at it.
When he was finished, the diagram looked very similar to the one below.
When looking at the diagram, staffing should always be on top. Staffing (i.e., your crew) is the most important part of this diagram and of all fireground operations.
Sharing a corner with staffing is application rate, an often overlooked part of incident management. Officers often calculate how much water they will need, but forget how it is going to get there.
On the left side of the diagram is needed fire flow, or how much water is needed for the length of time you will be at an incident. Needed fire flow is directly across from application rate because you need to know one to calculate the other.
At the base of the diagram is water supply. Water supply shares a corner with needed fire flow because of their mutual importance. It also is the basis of the decision-making process, raising the question: Can I put this fire out with what I have?
Staffing
Staffing has always been an issue for us, and always will be. We must understand is that it takes a certain number of firefighters to get the job done. There has to be an officer–the designated adult. Somebody has to drive the apparatus to the incident and operate the pumps and equipment. How many of us trust a fire engine, even a new one, to pump itself? Now, how many departments use the “set-it-and-forget-it” method of pump operation? I have heard of drivers who set the engine into pump gear, start to flow water, then pack out and fight fire. Of course, you also need firefighters. Fires, like wars, are fought and won with boots on the ground.
Application Rate
The application rate is the amount of water in gallons per minute that is applied to the fire, or more specifically, to the seat of the fire. It will be based on the number of firefighters, the available water supply, the hose/nozzle selection, the pump capacity, and the needed fire flow. The chart below gives a general guide for water application rates for fire suppression. It is solely a guide for establishing minimums. Only through practice, training, and real-life experience can we develop a more precise application rate.
If you are calculating your application rate capabilities as you arrive on-scene, you are too late. Company officers must work this out before the fire. Take the time to pre-plan your abilities.
Needed Fire Flow
The National Fire Academy method for calculating needed fire flow is one of the easiest.
This calculus is for a structure that is 100-percent involved. A good example of this is a 1,500-square foot home. The needed fire flow would be 500 gallons per minute (gpm). If in your estimation only 25 percent of the home is burning (room and contents-type fire), you would figure 25 percent of 500 gpm, which equals 125 gpm. It is evident from our chart in the application rate section that this can be achieved with a crew of two or three firefighters and a 1 ½-inch handline.
Any exposures get 25 percent of the needed fire flow also, where an exposure is any building, home, or object within 30 feet of the fire. In today’s suburban sprawl, it is not uncommon to find property line setbacks as close as five feet, so exposures are a real issue.
However, this formula does not reflect is the time it would take for the needed fire flow to extinguish the fire or any special situations caused by unusual building contents. Your training and experience as a company officer should give you the ability to adjust the amount of water for any given circumstance.
Water Supply
Even with modern fire suppression advancements and achievements, we still use the same firefighting agent we have used for centuries: water. A crew must have a good water supply or the capabilities to get water for the firefight. For those of us who work in a primarily urban area with a developed water system, this is a simple matter of finding the closest hydrant and connecting a hose. For those of us working in a more rural area, the need for alternative water sources is a constant challenge. To clear up any questions or differences, keep this mind: If you are going to start an aggressive offensive attack, have a water supply ready to go. A 500-gallon booster tank is just enough water to get your crew deep into a fire and then not get them out.
Common Corners, Common Goals
The diagram has a diagonal line the divides the square in halves to show that needs that share a common corner are mutually dependent on one another, namely staffing and application rate, and water supply and needed fire flow. With the exception of master streams, aerials, and unmanned monitors, the more water you flow, the more staff you need.
How often have you trained on advancing attack lines using a 1¾-inch preconnect, and then at the next fire, your crews automatically reach for that line? Training your crews on deploying different types and sizes of lines will greatly aid you at the next fire.
An idea of how much water you need will be the basis for choosing the water supply. Water supply and needed fire flow share a common corner because of this connection.
There are countless methods, techniques, and shortcuts out there to aid us in our jobs as company officers, but no one of them is a perfect fit. The many facets of your training, experience, and confidence will factor in your ability to be the leader that your crew, your department, and your community deserve. Dedicate yourself not only to your career but to a life of constant learning and improvement. The Thompson Diagram is a good tool to help you put your incident action plan in motion and assist in fire scene organization.
Note
Assistant Chief Thompson passed away six weeks after he retired from the Owasso (OK) Fire Department in a ranching accident. It is a loss that we will not soon overcome.
Kristofer M. DeMauro is a captain with the City of Owasso (OK) Fire Department, serving the fastest growing city in Oklahoma. He has been with the Owasso Fire Department for 14 years, with 20 years of combined paid, volunteer and EMS experience. He is a rescue specialist with Oklahoma Task Force One, USAR Team. A nationally registered paramedic, he has taught fire and emergency classes for Oklahoma State University, Kansas University, and the Tulsa Technology Center. He is a contributing editor to IFSTA and a published author. He can be reached at kdemauro@cityofowasso.com.
