Alerting people to the presence of fire is important. But, so is putting the fire out. When a fire starts, it quickly heats the air directly above it. This air rises and is pushed out to either side when it hits the ceiling. As this hot air reaches a sprinkler head, the sprinkler head is activated.
A sprinkler head will activate at a certain ambient temperature which is usually between 135 and 165 degrees Fahrenheit (57 to 74 Celsius). Most sprinkler heads are equipped with a glass container filled with a glycerin-based liquid that expands. At the pre-set ambient temperature, the glass will break and activate the sprinkler head. The sprinkler head is attached to a system of pipes that are hidden behind the walls or ceiling. These pipes wind through the building and outside to connect with a reliable water source. When the sprinkler head is triggered, a valve to the pipe system is opened, releasing the water that is kept under pressure from the pipes. The water is quickly pushed out of the pipes through the sprinkler head, spraying water downward and out to the sides.
The most commonly used sprinkler system in commercial buildings is a wet pipe system, which is composed of steel pipes that are always filled with water (hence, the term “wet”). The water in the pipes is under a moderate amount of pressure. When the sprinkler head is activated, the pressurized water in the pipes is immediately released, providing reaction faster than any other type of system. The wet pipe system is also the simplest and most reliable, boasting cost savings for easy installation and low maintenance. However, wet pipe systems are not always the best choice. Since the pipes are always filled with water, they’re not recommended for locations where the pipes might freeze or in residential environments where accidental leaks could be detrimental.
In a dry pipe system, the pipes are not filled with water; they are filled with compressed air. When the sprinkler head is activated, a valve releases the compressed air through the sprinkler head. Once all of the air is released, the pressure in the pipe changes, allowing water to fill the system. Dry pipe systems have a slower reaction time (up to a minute delay). To make up for this, dry pipe systems release a larger amount of extremely pressurized water, which requires larger pipes (and a larger budget). And, while a leaky pipe in a dry pipe system doesn’t pose a flooding threat, maintenance to the system is more complicated and costly.
Pre-action and deluge systems are variations of the dry pipe system. Pre-action systems must be triggered twice before water is dispensed from the sprinkler head. The first triggering allows water into the pipes. The second triggering releases the water, pushing it through the sprinkler head to extinguish the fire. This type of system provides added protection against false sprinkler head activation. If a sprinkler head is falsely triggered, an alarm will sound, but no water will be released, since the pipes remain dry until the second trigger has been activated. The chance of a sprinkler head to activate accidentally is one in 16 million.
In a deluge system, water enters pipes when triggered by a heat or smoke detector. There also may be a manual function such as pushing a button or pulling a cord to activate the system. All of the sprinkler heads in a deluge system go into operation simultaneously. Deluge systems are usually installed in chemical plants or other areas where the spread of fire would be exceptionally hazardous.