The general concept of a fire sprinkler system has been around since the early 1800s and consisted of a manually-operated system using perforated pipes to deliver water to an area. By the late 1800s, the first automated sprinkler system was invented, which to this day is still the foundation for nearly all types of modern-day sprinkler systems. A properly designed automated sprinkler system will detect the fire, initiate alarm, and begin discharging water within several minutes after a flaming fire establishes itself and begins to grow. Today, there are several different types of sprinkler systems available in the industry to accomplish this goal, each with its own benefits.

Wet Pipe Sprinklers

Wet pipe sprinkler systems are the most common type used today. In a wet pipe system, water is constantly maintained throughout the pipes. Upon sprinkler activation, water is immediately discharged from the activated sprinkler. The benefits of this type of system include:

  • Relatively low system installation and maintenance costs
  • Ease of modification
  • Overall system simplicity (and therefore a high degree of reliability)

The main disadvantages of wet pipe systems are:

  • They are not suited for sub-freezing environments
  • Damage to piping or sprinklers will likely result in water leaks and subsequent water damage

Dry Pipe Sprinklers

Dry pipe sprinkler systems are commonly used for applications where freezing is possible (i.e., ambient temperatures below 40° F. In a dry system, air or nitrogen is maintained throughout the pipes. Upon sprinkler activation, the air or nitrogen is discharged from the activated sprinklers reducing the pressure, which releases water into the pipes resulting in water discharging from the activated sprinklers. In addition to dry pipe systems being a great option for sub-freezing environments.

Dry pipe sprinkler systems have certain disadvantages, including those listed below.

  • Dry pipe systems are more complex to design than wet pipe systems
  • They require additional maintenance effort and cost
  • They result in higher installation costs

Preaction Sprinklers

Preaction sprinkler systems are commonly used in environments considered particularly sensitive to water damage and are designed to minimize accidental discharges. Similar to dry pipe sprinkler systems, air or nitrogen is maintained in the system and the system is pressurized. The key difference is that sprinkler system operation is controlled by an electrically operated valve triggered by a detection system. There are two main types of preaction systems:  single interlock and double interlock. A single interlock preaction system allows water to enter the system upon an alarm signal from the detection system. The system then operates similar to a wet pipe sprinkler system, discharging water immediately upon sprinkler activation. In this arrangement, the air or nitrogen maintained in the system provides supervision of the integrity of the piping (notifying the fire alarm control unit in the event of a leak), but does not directly control system activation.

A double interlock preaction system is similar to a single interlock system with the added feature that water will only enter the sprinkler system upon both an alarm signal from the detection system and activation of at least one automatic sprinkler. The benefits of preaction systems are:

  • They may be installed in sub-freezing environments
  • Additional protection is provided against accidental discharge

However, facility owners need to consider that preaction systems require additional cost for a fire detection system, are more complex than a dry pipe system, and require additional maintenance effort.

Deluge Sprinklers

Deluge sprinkler systems are commonly used in high hazard applications that require a significant quantity of water to control the growth and development of a fire. Like preaction sprinkler systems, deluge sprinklers are controlled by an electrically operated valve triggered by a detection system. The key differences are that deluge sprinklers are designed with an open orifice and the pipes are not pressurized. Upon activation of the system, water fills the pipes and is discharged through every sprinkler in the system simultaneously. Because water is not constantly maintained in the pipes, deluge sprinkler systems are a good option for sub-freezing environments. In addition, the quick application of large quantities of water helps to control or suppress fast-growth fires.

If you are considering a deluge sprinkler system for your facility, it is important to know that this type of system may require a strong water supply, additional cost for a fire detection system, and additional maintenance effort like that of a preaction system.

Foam-Water Sprinkler Systems

Foam-water sprinkler systems are commonly used in applications protecting high hazard commodities, such as flammable liquids. These systems are designed to deliver an adequately proportioned solution of foam-water at specific flow rates. The specific ratio of foam concentrate to water is controlled and metered by a proportioning device based on the design. These systems may be designed to operate in a manner similar to a wet pipe, deluge, or single interlock preaction sprinkler system, depending on the specific application. The foam-water solution is very effective in smothering the fire, suppressing combustible vapors, and preventing fire rekindling, which often allows for a reduction in the required water demand. A smaller water demand allows for smaller system pipe sizing and a smaller water supply.

As you can imagine, these types of systems are costly due to the added system complexity, which also results in additional maintenance. Additional system components include:

  • Bladder tank or foam pump
  • Proportioning device
  • Supply of foam concentrate throughout the lifetime of the system

You can see that we’ve come a long way since the simple system of uncharged pipes with perforations in the 1800s, to the present-day sprinkler systems that are designed to protect unique hazards and storage arrays. While it may seem like a simple aspect of fire engineering, 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. If you’d like to learn more about choosing the right fire sprinkler system, check out our two-part series here.