Why is Water a Quality Suppressant?

MeyerFire University | G203.07

By Edward Henderson, Sr., PE

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• Notes Page

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TRANSCRIPT

Why is water a quality fire suppressant?

WATER

Have you ever stopped and thought about why we use water to suppress fire? Today we’re introducing why water is our most commonly used fluid for suppressing fires worldwide.  

UNIVERSALLY AVAILABLE

There are a few reasons:  

Water is almost universally available. It’s a critical component of human life, so over human history we’ve naturally gravitated toward areas with ample water supply. That’s a good thing for fire suppression. Even when facilities are not located near water, it’s often possible to transport and store water nearby to use as a suppressant. Water is easy to store, pressurize, and move through pipe networks from one source to another. 

INEXPENSIVE

Water is relatively inexpensive. Especially compared to other fluids, water’s availability and access means it’s rather inexpensive. If every time we tested or drained a system and there was a major cost impact – then fire suppression itself might look a lot different. In areas that aren’t affected by drought or water shortages, that’s usually not the case though. Municipal water supply regularly filter and treat water on a scale that makes it rather inexpensive and a great fluid for our purposes.   

PREDICTABLE

Water has very predictable physical properties that make it a great suppressant. 

It freezes at 32 F (0 degrees Celsius) and turns to steam at 212 F (100 degrees Celsius).   

Water can absorb an amazing amount of heat. One pound of water can absorb 9,330 BTUs of heat from a fire because of phase change – changing from a liquid to a vapor. This means that when thrown against an object undergoing pyrolysis, our fancy word for fire, it absorbs the heat and “cools” the fire. Water is extremely effective in this regard.  

INCOMPRESSIBLE

Water is not compressible. Fluids can be compressible or incompressible. Water as a liquid is generally considered incompressible. A gallon or liter of water can’t easily be compressed into a smaller volume. At a given elevation the static pressure in all parts of the suppression system is constant. This changes once the water begins to flow due to friction losses.  

Water is referred to as “the universal solvent” because many more substances dissolve in water than in any other chemical. Water doesn't dissolve everything. Nonpolar molecules don't dissolve very well in water, including many organic compounds, such as fats and waxes. It is called the universal solvent because it dissolves the most substances, not because it dissolves every single compound. 

DIFFICULTIES OF WATER

What makes water difficult as a fire suppressant?  

Water, when mixed with oxygen, will corrode metal. This oxidation process can eat away at pipe walls and limit the lifespan of a fire protection system. We have relatively new and better ways to combat corrosion than we ever have, but it’s still a limiting factor in our ability to maintain systems for long periods of time.  

INCOMPATIBILITY

Water is incompatible with some burning hazards. Oils and metal dust, for instance, react with water and can create a more hazardous situation than before water was applied. 

DAMAGE

Water can damage assets. Early suppression with water will limit the amount of burnt products, limit smoke damage, and limit the danger to human life. Water will often also damage portions of the product or building that a system protects. This downside is usually overstated by building owners, but it is one downside to the use of water. 

FREEZING

Water is prone to freezing. While it’s predictable and often kept in conditioned temperature ranges, water freezes in non-tempered environments. This is a challenge that has to be overcome by heat, alternative system types, or alternative suppressants. 

SUMMARY

What makes water a great fire suppressant? These three main factors – availability, low expense, and ability to absorb heat. 

I’m Ed Henderson, this is MeyerFire University.