I believe the 2 ½” hose is “the line” of the modern fire service. In the early 20th century when the fire service became mechanized 2 ½” lines were the choice for most departments. The 2 1/2" served a dual purpose as attack and supply line. The 2 ½” hose has desirable qualities of high volume flow and low friction loss at a manageable weight. When paired with the smooth bore nozzles (almost exclusively used in the early 1900s) firefighters had in their hands a quality stream with good reach in spite of the pressure challenges of early pump technology and limited supply infrastructure.
Since then there has been subtle but steady change in our 2 ½” hose. The demands for higher flow, lower friction loss and lighter weight hose from modern firefighters have pushed manufactures to meet them. These adjustments are not ill intended, however, in the context of the 2 ½” attack line the point of diminishing returns is quickly breached.
As much as we would like to trust that hose manufactures are reducing friction loss and weight through technological advances in materials, it just isn't the case. The greatest factor in decreasing friction loss and increasing flow is the internal diameter of the hose. As the internal diameter expands friction loss is reduced and more water can be moved through the line.
If pump charts are not adjusted to the specific friction loss characteristics of the hose hose in service and coefficients associated with a true 2 ½” internal diameter are used, the line will be over pumped. This extra pressure results in increased nozzle reaction and ultimately a more difficult line for the nozzle firefighter to manage. In conversations at my department regarding this topic most will counter with “come on, it is only 4 or 5 pounds and we round up anyway”. They are correct in the sense that historic calculations for friction loss through 100’ of 2 ½” at 250 GPM is roughly 15 PSI and in modern hose it is around 10, but If you look beyond the “small” 5 PSI difference and view it as a percentage you will see that we are over pumping the line by 50%.
An increased internal diameter also increases volume inside the hose which translates to more water and more weight when charged. I myself was a part of the push at my department to change our high rise hose packs to lighter weight 2 ½” hose. With a bliss only ignorance can buy I was excited when we placed our high rise packs into service and had reduced the weight of each hose pack by 9Lbs. What I failed to recognize was how the manufacture achieved the lighter weight product, I trusted it was done without compromise.
Traditional style rubber lined double jacket hose Light weight single jacket style hose
Our light weight hose is essentially a single jacket hose where the traditional liner has been impregnated in the outer jacket. No different than the lightweight building construction we dedicate so much discussion to; the light weight construction in our hose has been achieved through material reduction. This elimination of the inner liner to reduce weight also increased the internal diameter to nearly 3”, so the hose is 9 lbs lighter per 50’ when we are carrying it dry but nearly 60lbs heavier per 100’ charged when we are operating under fire conditions. Because of these changes it is also more vulnerable to damage and kinking due to the thin exterior and minimal forces required to compromise it.
The fire hose is the life line of fire suppression and for too long I personally have taken it for granted as something that will always be right and just. Through the work of Dennis LeGear at LeGear Engineering and Fire Department Consulting , reviewing incidents across the country including information recently released regarding the line of duty deaths of Lt. Ed Walsh and firefighter Michael Kennedy of the Boston Fire Dep..., my eyes have been opened to the need for us to take a much closer look at our fire hose.
If you are following the work of Mr. LeGear, I would bet you too are concerned. If you haven't, I encourage you to click on the two links above and then head out to your engines and contact your local fire hose supplier to see what you find. I hope you are pleasantly surprised but I caution you; many who have taken this challenge have discovered these issues and more in their hoses are in fact right under their noses. As frustrating as it may be thankfully it is discovered as part of a challenge and not part of an investigation.