Just Like the Movies: Deluge Fire Systems

by Mike Lehner, P.E. and Paul Greenwalt, EIT

This article is part of Wood Harbinger’s newsletter series.

You know the scene. Action movie: Good guy running from the bad guys, gun shots, explosives, smoke. Fire starts in one small area and the ENTIRE fire sprinkler system begins dumping water on the building. Or how about the high school drama where the kids are smoking in the restroom and the whole school evacuates while being doused with thousands of gallons of cold water while the alarm system blares its warning. We all know that this is fake and completely made up…. Isn’t it?

In a typical building fire suppression system, fire sprinkler heads do not all open simultaneously.  Sprinkler heads react to heat; they operate using either a liquid-filled bulb or a thermal fuse inside the head that breaks at a certain temperature, as determined by the specific application. Most fires start out small. If the sprinkler system is properly designed, most fires will generate only enough heat to trigger one or two sprinkler heads, which open to contain and maybe extinguish the fire. The rest of the sprinkler heads would not open since they are not exposed to higher temperatures. They likely would not even require maintenance after the fire event.

Back to Reality

What if I told you that the movie scenes described above were not myth? That’s right, such systems DO exist! It’s just that the application shown in movies is all wrong. Systems where all the sprinkler heads activate at once are called deluge fire systems. Deluge fire systems are designed to protect against high-heat and fires with accelerated growth rates. The purpose of such a system is to mitigate fire spread and allow safe egress, that is, a path to safety for building occupants.

How Deluge Fire Systems Work

Deluge fire sprinkler systems are nearly the same as traditional wet pipe sprinkler systems, except that the distribution piping is normally empty and unpressurized, and ALL of the sprinkler heads are open and ready to discharge water. A deluge valve is located at the sprinkler riser room and is normally closed. It can be opened with an electric signal, pneumatic signal, or even a manual release. Typically, deluge systems use an array of electronic sensors to detect a fire event and report that event to the fire alarm panel. Sensors include triple infrared (IR), heat detection, manual activation. Triple IR devices monitors different wavelengths of light for signs of a fire. Heat detection monitors for heat in a localized area, which include heat detection wire or a spot type heat detector.  Finally, manual release may be used as well.

Opening the Deluge Valve

If the sensors report need for a deluge response, then the panel will open the deluge valve. This allows water to flow into the open fire protection piping, out through the sprinkler heads, and douses the entire area served with water. There may be several deluge valves throughout a facility to separate different areas so that one event does not flood the entire building. As you can imagine, flowing all the sprinkler heads in a deluge zone poses a large demand on the fire water system, and usually calls for larger piping systems as well as smaller deluge system sizes. Normally, the fire water service to the building is not capable of protecting the entire building at once. If there are multiple areas in alarm and are operating simultaneously, then the building is in more trouble than fire sprinklers alone can handle, and the fire department had better hurry up!

Deluge Fire System Uses

Deluge fire systems are used in areas of high hazard and/or where large groups of people may be exposed to a fast-growing fire. Examples include aircraft hangars, airports, refineries, water spray for fuel tanks, and power and chemical plants. There are also varieties of deluge fire systems that introduce foam into the system to suppress fuel fires. Selecting a deluge fire system is very application-specific, so care must be taken to go over the project with the owner to determine the facility uses, what type of system should be employed, and where.

Realistic Portrayal

Let’s go back to the movies and dissect a scene where the good guy runs across screen and one bad guy jumps out with a flame thrower. What happens next? If there’s a deluge fire system in the space, the detection device nearest the flame thrower senses a temperature increase and reports this to the fire alarm panel, which determines that this is a fire event. The deluge valve opens, water begins to flow. Let’s say the area has 20 sprinkler heads, and the 4-inch pipe the serves them is connected to a 60psi water supply. With an ordinary hazard density, or possibly even more, this system would discharge 900 gallons of water per minute. This would flood the area in one foot of water (2,500 square feet) in under 21 minutes. This is about 156,000 pounds of weight. Fortunately, this 63 PSF load would not bring the floor down. But the waterworks going down stairwells, chases, and such would be spectacular…definitely something worthy of the big screen!

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