Getting water flow right is a crucial component of firefighting operations and it’s the key responsibility of the pump operator. Determining the pump discharge pressure for each line requires the operator to know the gallons per minute (GPM) flow, which depends on the selected nozzle and operating conditions. The hose size and length must be taken into account, along with any appliances or gates that would affect flow.
Finally, the pump operator can calculate fire hose friction loss, which helps them to deliver water at the right flow rate and pressure for the crew to fight the fire safely and effectively. But what causes fire hose friction loss, how is it calculated, and what can be done to reduce it?
What Causes Fire Hose Friction Loss?
Fire hose friction loss is the reduction in water pressure caused by resistance as water flows through a hose. Friction loss is also present in pipes, hose fittings, and other components of a water delivery system.
Several factors can influence fire hose friction loss, including:
- Age and condition of hose
- Length of hose
- Hose type, weave, and quality
- Hose lining
- Water flow (gpm)
- Water turbulence
- Gravity
- Hose diameter
- Kinks, bends, and restrictions
Elevation changes also affect the pressure required for water delivery, although elevation pressure is calculated separately from friction loss.
According to the National Wildfire Coordinating Group¹, friction loss is quadrupled every time flow is doubled. Relatedly, increasing hose size decreases the friction loss, as the fifth power of the hose diameter².
When the pump operator knows the friction loss, they can adjust the pump discharge pressure, thereby producing the desired nozzle pressure.
How to Calculate Fire Hose Friction Loss
One of the most common methods for calculating fire hose friction loss is using a mathematical formula. Fire hose friction loss calculators and reference charts use established relationships to estimate pressure loss based on flow rate, hose length, and hose characteristics.
A common firefighter friction loss formula is this:
FL = C * (Q / 100) ^2 * L / 100
Where:
- FL = Friction loss in PSI
- C = Friction loss coefficient (or friction loss factor)
- Q = Flow rate in hundreds of gallons per minute (GPM ÷ 100)
- L = Hose length in hundreds of feet (feet ÷ 100)
Generally, C is understood to be a constant that combines hose diameter and roughness, but it is not a precise measurement³, as diameter and roughness can affect flow differently. That’s why published data doesn’t always match up to verified flow meter testing. Friction loss coefficients can be found in firefighting training materials and hose performance references.
Note: The Fire Protection Research Foundation⁴ and others believe that standard rules of thumb regarding fire hose friction loss calculations may be too conservative, as they are based on dated hose technology. Advancements in hose fabrication have reduced friction loss, and using outdated calculations could cause excessively high pump discharge pressures.
However, friction loss tables are still useful as a starting point for friction loss calculations. The tables typically show GPM on one axis and hose diameter (100 ft) on the other.
You can access fire hose friction loss charts or cheat sheets⁵ for the most common hose sizes. These will give you the FL for a certain GPM measurement, which you can then use in calculating pump discharge pressure.
Another Fire Hose Friction Loss Method
Calculating friction losses using a mathematical formula is not always the best way to operate on a fire scene, where time is limited.
In the field, it’s more helpful to understand how to figure out fire hose friction loss without resorting to paper and pencil. You can simplify your calculations and still arrive⁶ at a working pump discharge pressure suitable to the situation at hand. Memorizing common nozzle sizes, flow rates, and hose configurations used by your department can help make these estimates faster.
The Hand Method for Friction Loss
When you know hose size and GPM, you can use what’s known as the Hand Method to arrive at a rough estimate of friction loss. The Hand Method⁷ for friction loss requires you to memorize the GPM for your nozzle (fog or smooth bore). It’s not your standard friction loss formula, but it still gets the job done.
Assign each GPM setting to a finger: 95 GPM to your thumb, 125 GPM for your index, 150 GPM for middle, 175 GPM for ring finger and 200 GPM for your pinkie.
Number each finger, 1 through five, starting with your thumb.
Finally, imagine 12 at your palm (for 1 ¾” hose). When you need to calculate friction loss, find your desired GPM and multiply by 12. If you need 125 gpm on 100 feet of hose, that corresponds to number 2 on your finger. Multiply 2 by 12 to get 24; your friction loss is 24 psi. (You can double check this technique using a friction loss table.
The hand method is not precise, but it will get you close to where you need to be when a fire is blazing.
Ways to Reduce Fire Hose Friction Loss
Are there any ways to reduce friction loss in fire hoses? While friction loss is a fact of life when fighting fires, there are ways to minimize unnecessary pressure loss and improve water delivery efficiency.
1. Maintain Your Fire Hose
The first, and easiest, method for reducing unnecessary fire hose friction loss in fire hoses is to ensure the upkeep and maintenance of your hose and equipment. Kinks, internal obstructions, and damaged hoses can restrict water flow and increase pressure loss. Keeping hoses (and other equipment) in good working order reduces that effect.
Store and transport your fire hose with care. Avoid kinks and make sure there is plenty of air circulation. Keep it clean after coming into contact with dirt, oil, and chemicals, and protect the outer jacket from abrasions. Also, make sure the hose isn’t punctured or pierced, and check it regularly.
2. Increase Fire Hose Diameter
Secondly, increasing the diameter of the hose will generally decrease water flow and the associated friction loss.
Therefore, just going from a 1-inch diameter hose to a 1 ½ inch diameter hose could decrease the friction loss by a factor of 7⁸.
3. Reduce the Nozzle Tip Size or Pressure
Maintaining pressure while reducing tip size will reduce friction loss, and maintaining tip size while reducing pressure will also reduce friction loss.
However, these methods will result in decreased flow, which could hamper your efforts. Any changes must preserve the water flow and nozzle performance required for safe and effective firefighting operations.
4. Improve Fire Hose Quality
Finally, modern fire hose construction can help minimize friction loss through smoother interior linings and improved water flow characteristics. High-quality fire hoses may offer less resistance than older or deteriorated hoses, depending on their design.
Reviewing manufacturer specifications and verified hose performance data can help departments choose equipment that supports efficient water delivery.
Fire hose from Rawhide Fire Hose is designed for dependable performance in demanding firefighting applications. Whether you choose single-jacket or double-jacket fire hose, fire engine booster hose, or any other kind of fire hose, Rawhide offers durable options for a variety of firefighting needs.
Reduce Fire Hose Friction Loss
Rawhide fire hose is built for lasting performance and durability, giving you high-quality fire hose with quick turnarounds, even in custom configurations.
Selecting the appropriate hose diameter, maintaining equipment, and understanding friction loss calculations can help firefighters deliver water more efficiently.
Contact one of our specialists for questions on firehose friction loss or to find out how we can help you improve your equipment and increase your efficiency.
References:
¹https://www.nwcg.gov/course/ffm/squirt-water/33-friction-loss-in-fire-hose
²https://d3at0mnwuyeh75.cloudfront.net/content/dam/fe/online-articles/documents/FEU/SpurgeonOct12.pdf
³https://www.firerescue1.com/fire-products/fire-apparatus/articles/how-to-calculate-and-overcome-friction-loss-k79PfBh4sTCRaWZr/
⁴https://www.nfpa.org/-/media/Files/News-and-Research/Fire-statistics-and-reports/Emergency-responders/RFFireHoseFrictionRevised.ashx?la=en
⁵https://frictionlosscalculator.com/compact-table
⁶https://www.nwcg.gov/course/ffm/squirt-water/34-calculating-engine-pump-pressures
⁷http://static1.squarespace.com/static/5920b67a197aea2df13b38a3/5923356e365ffa63a823aa5d/5923354a365ffa63a823a879/1495479626047/Hand-Method-for-Friction-Loss.pdf?format=original
⁸https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5239062.pdf
