What Properties of Fluids Do We Quantify?

MeyerFire University | G301.01

By Edward Henderson, Sr., PE

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G121 SERIES

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NOTES & SUMMARY

• ​One-Page Summary [PDF]
• Notes Page [PDF]​

G121 SERIES

1. What properties of fluids do we quantify?
2. What are the basic principles with hydrostatics?
3. The relationship of elevation and pressure?
4. Difference between pressure and head?
5. Exercise: Water Tower Height
6. Exercise: Maximum Standpipe Height
7. Exercise: Minimum Fire Pump Size
8. What is potential energy?
9. ​What tools do we use to measure pressure?

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TRANSCRIPT

What properties of water do we use for fire suppression?  

WATER PROPERTIES

In this video, we’ll explore what properties of water we typically care about when we’re talking about fire suppression.  

PRESSURE

The first is pressure. 

Pessure is a force within a fluid that acts in all directions. It is a force divided by unit area. In imperial units, it is usually described as pounds per square inch, or PSI. For SI, this is usually in Bar. The minimum pressure for a typical sprinkler, for example, is 7 psi. This means that at the sprinkler, the water pressure when it’s flowing through the sprinkler opening should be 7 pounds per square inch in order to fully develop the sprinkler spray pattern.  

FLOW

The second property concerning fluids that we care about is flow. 

Flow is a quantity that describes the volume of fluid divided by the time it takes to travel. It’s a volumetric speed, if you will, that in imperial terms we quantify as gallons per minute, or GPM. In SI units, that’s often in liters per minute. Flow through a standpipe hose valve, for example, might involve 250 gallons per minute through the hose opening.  

WEIGHT

A third property that we care about is the weight of water. 

A cubic foot of water weighs 62.4 pounds. When water is stacked on top of itself, the weight of the water column at the top creates more pressure relative to the water column at the bottom. This is elevation pressure that is due to the weight of the water. In imperial terms, it translates to 0.433 psi/ft of elevation. So, what that means is water head pressure is the static pressure caused by the weight of water solely due to its height above reference point. The pressure at the bottom of a 40-foot lake or a 40-foot tube would be identical, since only height is involved. To deliver water to a height of 100 ft would require 43.3 pounds of pressure just to lift the water to that height. – this is a static loss. 

WET SUPPRESSION SYSTEM

Applying these properties of water to a wet suppression system brings this all together. 

The design objective is to deliver quantities of water sufficient to control the spread or fully extinguish a fire within a facility.  

There must be enough pressure to overcome pressure lost due to elevation and pressure lost due to friction within the pipe network, the quantity of water is dictated by the hazard, and the weight of the water and the pipe must be supported by the facility structure and additionally resist momentum and seismic loading.

SUMMARY

As a fire suppressant, the properties of water that we’re most concerned with integrate system pressure, the quantity of water (system demand), and the structural integration in the facility to be protected.  

I am Ed Henderson, this is MeyerFire University.