Read full post: How Does a Pre-action Fire Protection System Work?

Summary: Understand pre-action fire sprinkler systems and the best environments for them.


  • How do pre-action fire sprinklers work?
  • What environments need pre-action fire sprinklers?
  • What is the different between different sprinkler types?

An Introduction to Pre-Action Fire Sprinkler Systems

When it comes to fire protection, businesses have several options. The only universally unacceptable option is to have no protection at all. Fire suppression systems fall into three fundamental categories: wet pipe, dry pipe, and deluge. Pre-action fire sprinklers fall right in between all of these.

Pre-action pipes start out as dry pipes; they hold water back using an electronic “pre-action” valve. This system requires two events to happen before any sprinklers discharge:

1.     The pre-action valve will only activate when an independent fire detection system detects a fire. Upon alert, the pre-action valve releases, water flows in, and the system essentially becomes a wet pipe system.

2.     Now that water is on deck, one or more individual sprinkler heads need to release to engage and discharge water.

Why Choose a Pre-Action Sprinkler System?

Pre-action systems offer several advantages. It’s not uncommon for sprinkler heads to be falsely triggered. Accidental activation often results in costly, irreversible property and water damage. The two-event discharge requirement adds an elevated level of protection from such inadvertent discharges. The use of pressurized air or nitrogen in the piping system allows for the easy detection of leaks.

Locations that house water-sensitive property need pre-action systems such as archival vaults, rare book libraries, fine art storage rooms, and computer data centers. Due to the unique fire hazards that cold storage warehouses present, pre-action systems are especially useful. The water from an inadvertent discharge in a cold warehouse would freeze immediately, a problem as expensive as it is inconvenient.

What’s the Real Difference Between Wet Pipe, Dry Pipe, and Pre-Action Fire Sprinklers?

Wet Pipe Sprinkler Systems: Today, wet pipe sprinklers are the most popular system. They are effective, low-cost, and low-maintenance. The pipes remain filled with water. Once the heat-sensitive sprinkler heads are triggered, water flows through the activated sprinkler to the direct source of the fire. This system has the quickest reaction time but run the risk of freezing in cold environments.

Dry Pipe Sprinkler Systems: Unlike wet pipe systems, dry pipe systems are ideal when there is a potential for freezing. They do not carry water in the piping until activation. The pipes, filled with pressurized air and nitrogen, open a dry pipe valve to allow water in when a sprinkler head is triggered. The disadvantage to this system is the significant delay in response time that can occur between fire ignition, detection, and reaction.

Dry pipe eliminates the water leaks that occur with a wet pipe system, but the required maintenance is just as demanding. Unfortunately, although sprinkler corrosion happens in all systems, it is significantly more prevalent in dry pipe systems. The compressed air and oxygen that occupies the pipes create a breeding ground for corrosion.

Pre-Action Fire Sprinkler Systems: Like dry pipe systems, pre-action pipes do not hold water within the sprinkler piping and are instead filled with compressed air or nitrogen. Unlike a dry pipe system, the pre-action valve governs the flow of water. There are two types of pre-action systems:

Single Interlock: This system requires a single, preceding fire detection event to occur. This event is almost always through the activation of a heat or smoke detector. Once this happens, the pre-action valve allows water to enter the piping system. If a sprinkler head activates before this, it will sound a trouble alarm, but no water will discharge.

Double Interlock: Some businesses prefer the added layer of protection that a double interlock pre-action system provides. Double Interlock systems require that a preceding fire detection occurs in conjunction with an automatic sprinkler activation before water releases into the pipes. The activation of one alarm alone will not be enough.

Double Interlock systems are useful for the protection of extra water-sensitive items that cannot afford to be lost such as museum artifacts. However, they are complex setups that are high-cost and high-maintenance. Without routine and diligent maintenance, these systems run a higher risk of malfunction. Additionally, their response time is slower than that of a single interlock pre-action or wet pipe system.

Making the Right Decision for Your Business

There are four sprinkler options available today: wet pipe systems, dry pipe systems, deluge systems, and pre-action sprinkler systems. Each arrangement comes with a unique set of advantages and disadvantages. It is important to calculate and prioritize your fire suppression needs in conjunction with the building’s capabilities.

Pre-action sprinkler systems are an excellent solution for the protection of valuable property. With the proper engineering and maintenance, it is a reliable way to eliminate fire hazards and keep both your business and employees safe.

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