If you hold a cigarette lighter underneath a sprinkler, every sprinkler in the building will suddenly activate and spew water, right? Wrong. The heat from the lighter will cause only one sprinkler to operate, the one that feels the heat. We have Hollywood movies to blame for the widespread misconception that all of the sprinklers in the building will discharge water simultaneously when any single sprinkler feels enough heat. For a more detailed discussion on this Hollywood-supported myth, and the truth behind the myth, see our previous blog, “Lights, Camera, Activate! The Truth about How Most Sprinklers Activate”.

How It Really Works

A fire starts, the sprinkler system detects the fire, and water is discharged from the system, absorbing heat as it penetrates the smoke and the fire plume to reach the burning fuel source. This concept applies to all sprinkler systems, but the demands created by different occupancies and hazards vary substantially. To account for this, sprinkler systems vary in type and scale, and it’s crucial to use the appropriate system for the circumstances.

Another misconception about sprinklers is that they are triggered by smoke, just like smoke detectors. But sprinklers are actually triggered by heat, and are engineered to respond to a specific temperature. Furthermore, sprinkler systems can activate in different ways. While many rely on activation of the sprinkler’s heat sensitive element, some require that both a sprinkler and another means of detection activate before water can be discharged from the system.

Types of Sprinkler Systems

Sprinkler systems are typically grouped into four categories. The most common type of sprinkler system is a wet pipe system. The name is fairly intuitive; the main distinguishing characteristic here is that water remains, under pressure, in the system pipes at all times. This causes a faster reaction time and more immediate results in the event of a fire. In most situations, this is beneficial and preferred. In some situations though, having water in the piping can pose a problem, such as when the system piping is located in an area that is subject to freezing temperatures.

A dry pipe system is a common system type for use in areas subject to freezing temperatures. As you might imagine, the pipes are not filled with water, but with compressed air which keeps the valve that holds back the system’s water closed. When the sprinkler activates in response to heat from a fire, the air in the pipes is released, allowing water to open the dry pipe valve, and enter the piping. At all other times, air in the piping prevents the sprinkler system from freezing.

Alternative systems do exist and are often used in structures that house valuable or historically significant items. Pre-action systems, for example, utilize piping filled with compressed air, much like a dry pipe system. However, pre-action systems are linked to another type of detection equipment, which must activate in addition to the heat-sensitive element of a sprinkler before water can be discharged onto the fire. There are three variations of this system, but the preventative measure is the same; water will be discharged only if the threat of fire is verified by the detection and control scheme.

Deluge systems, on the other hand, are only typically used to protect highly combustible areas where the fire hazard necessitates large quantities of water quickly. This system is comprised of open orifice sprinklers. This means that, unlike the other systems just discussed, once a supplemental fire detection system is activated, the deluge valve holding back the water will open, and water will discharge simultaneously out of every sprinkler in system.

Sprinkler systems may seem like a simple aspect of fire engineering, but the selection and design of the sprinkler system that will protect what you most value is one of (if not the) most important decisions a facility owner can make. We can help you to determine which system works for you. If you have a particular need, I invite you to fill out the contact form below and one of our fire protection engineers will contact you soon: [gravityform id=”1″ name=”Contact Us”]