• HMA

Science, psi, gpm, and cheese

"Use big water to fight big fire, right?" 


Let's literally take this one from the macro level to the micro level. 


The macro view has us thinking about the strategy and tactics we know from our training and personal experience: a typical structure fire attack that uses the principle of more water = more fire suppression. 


The micro view has us zooming in and look at how water actually puts the fire out. 


Pause the visualization -- macro view -- of major fire incidents you have personally experienced and let's just talk fire science -- micro view -- for a minute. C'mon, it's only for a minute. 


Optimized droplet size. 

Surface area is a thing. This isn't new. Physics has long proven that transfer of heat energy into a cooling medium (in our case, water) occurs through the surface. Thermal energy -- heat -- can only be transferred at the point of contact between the cooling medium (water) and the heat product (fire). Objects (in our case, water droplets) which have a large surface area compared to their volume cool fastest. 


Stated another way, smaller water droplets absorb heat energy more efficiently because more surface area means more heat absorption. In Ultra High Pressure (UHP), by breaking down the water droplet into 64 smaller droplets, we create 10 times the surface area of a conventional water droplet.


A nozzle flowing water at ultra-high pressure

 

Optimized pressure. 

It's not sufficient or accurate to simply state that cranking up the pressure and breaking up water is going to improve efficiency. Our studies, along with many others, have consistently shown that optimal conditions for fire suppression are at 1450 psi flowing 20 gallons per minute (GPM). Note that as of 2016, the National Fire Protection Agency (NFPA) states that UHP is water flowing at pump pressures above 1100 psi. 


By combining optimized droplet size with optimized pressure, UHP has consistently put fires out faster using approximately 1/5 the amount of water. (For more on the science and to see some of the data, visit our "What is UHP?" page.)


The science is not debatable, so why so much discussion and debate around the use of UHP? 


Honestly, there are a lot of factors at work, especially in an industry as dynamic as the fire service. We're a vocal bunch with a lot of experience, tradition, and opinions that we bring to the table. 


In some cases, there is a false perception that UHP is simply the repackaged technology of John Bean high pressure pumps. These were manufactured from the late 1940s to the mid-1970s and operated between 600 and 850 psi. We're not sure why this one keeps coming up; it reflects a misunderstanding in the science and application of two different technologies. 


But the most likely reason is personal experience. Most firefighters have not personally used UHP technology (yet) and there's something about holding the nozzle and putting out the fire yourself (or observing nearby) that is incomparable. A big part of our job is to get UHP into your hands so you can personally take it from micro to macro level by seeing how it operates on the fireground. 


So give us a shout and let's book a demo. 


P.S. For a fantastic and very Wisconsin basic explanation of how smaller water droplets are more efficient (i.e. surface-to-volume ratios in heating and cooling), check out this cheese cube experiment.


In Wisconsin, using cheese to illustrate fire science comes with the territory.

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