Basic Types of Sprinkler Systems

Here is basic information about several types of sprinkler systems and how they operate.


As an example of Waterflow Alarm and Sprinkler Supervisory Services, an automatic extinguishing sprinkler system has a fire alarm control panel (FACP), a waterflow switch (which, in this case, is a paddle switch), and a valve tamper switch to monitor the water supply valve. Activation of the paddle switch causes an alarm at the FACP with operation of the notification appliances. Activation of the valve tamper switch causes a supervisory signal at the FACP. These systems are not to be confused with extinguishing/suppression release systems. They do not control the release of water or agents; they simply monitor the sprinkler system and notify personnel of any changes.


Pre-action systems have closed sprinkler heads. When the FACP goes into alarm, the FACP activates and opens the water solenoid valve. This action causes the sprinkler pipes to be filled with water. As soon as a sprinkler head activates due to high temperature, water is released.


Deluge systems have open sprinkler heads and require careful design to be effective and efficient. When the water solenoid valve is activated and opened by the FACP, the water is released from every sprinkler head. Usually, the FACP is programmed to activate the water upon activation of a single heat detector or only after multiple smoke detectors go into alarm. This requirement of more than one smoke detector in alarm before activating the water release valve is called “dual detector” or “cross zoning.” It is generally not desirable to release water on a single smoke detector alarm.


Fixed extinguishing systems are basically like any other system that releases agents for fire suppression. These systems are usually of the deluge type, but release fire suppression agents instead of water. Some examples of these agents are: CO2, FM200, Halon and AFFF foam. Some agents pose a health hazard to occupants and, if there is a release, a large volume of chemical will be expelled. Consequently, it is a good design practice not to release chemicals until the occupants are notified and had an opportunity to evacuate the hazard area.

The two FM categories have different requirements. Under FM, pre-action or deluge systems must use Style D (Class A) wiring on their IDC circuits and have 90 hours of standby power. It can be batteries, or generators, but it must be acceptable to the Authority Having Jurisdiction (AHJ). Sometimes a standalone charger and batteries from an outside vendor may have to be used to meet the 90-hour standby requirements. In these instances, you must confirm whether or not the control panel is capable of operating with stand-alone battery chargers.

All fire alarm initiating and notification circuit wiring must be supervised (monitored for integrity). On extinguishing/suppression release systems, both the circuit wiring and the releasing device (e.g., solenoid coil) must be supervised. This is a requirement of NFPA 72 and the applicable sprinkler standards. This means releasing service systems are unique in that the control panel must operate the solenoid valve and actually supervise the actuating coil.

Very interesting, thanks! Is this post in response to <URL url="Fire alarm myths]this topic[/url] in at all?

Anyways, aren’t there some instances where a manual alarm activation can cause the agent to be released?

Yes, it seemed to me there is some confusion about sprinkler system operation.

Yes. Many times manual activation is included. Many agent release systems have dedicated manual release stations in the release area and/or at the FACP.

Keep in mind the information in the first post is from basic FA training materials. It is not meant to be detailed engineering information.

You will also find a pre-action sprinkler system AND agent releasing system in the same area. Common in data centers, archives, or places that store historical items. There the agent releasing system is tripped via smoke detectors (sometimes cross zoned) and the pre-action is tripped via heat detectors. The theory being if the agent runs out and fails to control the fire, the sprinklers will be tripped. You get the benefits of a water based system in such a sensitive area if you need it.

And deluge systems can be activated by either an electric solenoid (activated by a releasing panel with smoke or heat detector alarms) or by pnumatic pilot lines (closed head sprinklers). The pnumatic method needs no electricity to activate the deluge valve.

Nice job. These diagrams are very informative. Are there typically sprinkler heads located in the plenum area above a drop ceiling?

On a side note: I move to have this thread stickied. Do I have a second?

I second this motion: I’m seriously considering taking a job at a sprinkler laying firm and I think this is good information.

Not usually. The only time I’ve seen it is when you have wood frame construction above the ceiling. Most commercial office buildings, schools, health care facilities are steel construction.