How Does a Fire Sprinkler System Work?

There are many myths and misconceptions about how fire sprinkler systems work to extinguish a fire in a building.

Sadly, such myths prevent most people from installing the systems in their buildings, mainly from fear of the misconstrued water damage from fire sprinkler systems that activate accidentally.

So, how exactly does a fire sprinkler system work? Before we dive into the topic, let’s discuss some basics first.

What Is a Fire Sprinkler System?

close up of fire sprinkler installed on red pipe

A fire sprinkler system is an “automatic” network of pipes installed in walls and ceilings that eject pressurized water when heat from a fire activates the plug or trigger.

The most common installation system involves installing pipes in the ceiling such that the sprinklers point downwards and release water from above to put out a fire developing under them.

When the pipes are installed in the side walls, the sprinklers point inwards and release water sideways to fall on the developing fire from the sides.

The pipes may also be installed in a loft space pointing up. This system is common on ship decks.

Pipes are installed when the building is under construction, adding about 1-2 percent additional cost. Buildings that do not already have fire sprinklers can be fitted with the systems during remodelling. This is called retrofitting, and it’s usually expensive.

Fire sprinkler systems are installed in residential and commercial buildings, although the uptake in homes is generally lower. The systems are common in commercial spaces like theatres, hotels, shopping complexes, warehouses, and factories.

Main Parts of a Fire Sprinkler System

petrochemical plant fire sprinkler

It’s easier to understand how a fire sprinkler system works when you know the parts that make up the system.

  • System cross and piping: The pipes are usually copper, steel, or fire-resistant plastic.
  • Automatic sprinklers: This is the section of the system that releases water onto the developing fire.
  • The plug: Also called the trigger, the plug has a heat-sensitive element that activates the sprinkler head when a fire erupts. Heat-resistant elements come in two main types (more on this later).
  • System risers: These are the pipes that connect the system cross and the main pipes to the building’s domestic water supply.
  • Water flow switch: This activates when water starts flowing through the system. It alerts the local fire department that the sprinkler system has been activated.
  • Motor gong: The gong sounds an alarm when water starts to flow actively in the system.
  • Pressure gauges: The gauges measure the pressure of the water in the system to check if it is sufficient to release the water efficiently if a fire arises.
  • Main drains: The water is drained into the main drains during routine system testing or maintenance.

How a Fire Sprinkler System Works

A fire suppression system may come in different types, but the underlying working principle is the same: when a fire erupts, the flames heat the air around them, which rises and spreads under the ceiling of the space. The resultant high temperatures offset the trigger, which activates the head, and the valves open to release water to flow downward, upward, or sideways in an outward arc.

The released water falls on the nearby flames to extinguish them and minimize smoke and heat buildup. This allows people time to evacuate the building and for the fire department to arrive, generally within 5-20 minutes.

The entire fire system is “automatic” and doesn’t rely on any electronic gadget or electrical system to work, as this would defeat the automation. Most fires cause a near-immediate breakdown or power cut in a building, and using an electrical device in the system means it wouldn’t come on when the device faces a power disconnection.

Although we call this an automatic fire sprinkler system, only the water-releasing mechanism is truly automatic.

If you accidentally set off a fire sprinkler or after a fire is extinguished, you must locate the main water supply to the system and cut off the supply.

The main water supply is usually located outside the building to prevent the fire from damaging it. It also becomes easier to access during a fire.

In most cases, you can switch off the water supply if you have ascertained that the fire sprinkler system came on accidentally. In the event of a fire, the fire department usually cuts the water supply once they confirm the fire has been put out successfully.

Contrary to popular belief that when a fire occurs every sprinkler goes off, only the activated sprinkler heads near the fire go off. One or two heads could be activated, depending on the location of the fire and its intensity.

Each activated sprinkler head can release 10-25 and up to 60 gallons of water per minute. The water is usually enough to put out the fire or suppress the smoke and heat until the fire department arrives at the scene.

Since each fire sprinkler head is activated on its own, the risk of water damage is minimal and confined to the area where the head has been activated. This setup eliminates what would be a counterintuitive aspect of trading fire damage for water damage.

How Is the Fire Sprinkler Head Activated?

close up of fire sprinkler on white roof

Forget all the myths that fire sprinklers can be activated by smoke and smoke detectors. If this were true, even burning food in the kitchen would activate the system, which doesn’t happen.

Fire sprinkler system triggers come in two types. None of these types can be activated by smoke or smoke detectors. Fire sprinkler systems and smoke detectors work hand in hand and are not mutually exclusive, so it’s prudent to have both simultaneously.

The most common type is the glass bulb trigger that contains a glycerin-based liquid that expands at fire-specific temperatures to break the glass and activate that specific head.

For most systems, the temperatures in the space have to rise to 57-74° Celsius (135-165° Fahrenheit). Again, this dispels the myth that ordinary temperatures could activate the system when there is no fire and potentially cause water damage.

The plug or trigger in some sprinklers is Wood’s metal, an alloy of cadmium, lead, bismuth, and tin. The alloy melts at a temperature of 71°C (160°F), which is within the range of fire-specific temperatures. This activates the head at that specific point in the system.

How Different Types of Fire Sprinkler Systems Work

Another interesting way to look at how fire sprinkler systems work is to consider how each type of system works.

The two types of fire sprinkler systems are wet pipe and dry pipe systems. So far, we have described the working mechanism of wet pipe fire sprinklers. They are the simplest, most common, and most reliable systems. Wet pipe fire sprinklers are mostly used in commercial buildings.

Wet pipe fire sprinklers are called so because the pipes always contain water, which is ready to release immediately after the heads are activated. While this offers the quickest response to a fire, it isn’t always the best option where fire sprinkler leakages are frequent.

Furthermore, wet pipe systems installed in extremely cold areas potentially pose water damage dangers.

If the water in the pipes freezes, the pipes expand and could burst, rendering the system malfunctional and causing water damage. This also means you wouldn’t have fire protection at that point.

Although it’s rare, accidental activations usually happen in wet pipe systems. The water damage from these sprinkler systems can be massive if you don’t know how to turn off fire sprinkler heads that go off accidentally.

To avoid accidental activations, you can use a Shutgun, our revolutionary fire sprinkler head shut off tool for cutting the water flow.

emergency sprinkler head emergency water stopper

The good thing is that if there’s truly a fire threat, or one arises from accidental activations, the quick-stop fire sprinkler tool has a patented fusible link that causes the sprinkler head to reactivate.

On the other hand, dry pipe fire sprinkler systems contain nitrogen gas or pressurized air instead of cold water.

When the trigger activates, the air or gas leaks out and causes a sudden pressure drop. This causes the valve to open and allows water to flow into the pipes from the main supply. The water then releases through the sprinkler head.

Dry pipe systems are usually installed in cold buildings that are often unoccupied and unheated. They are ideal in cold places where the pipes could burst when the water in them freezes.

A dry pipe sprinkler system eliminates the problems of water damage and system failure due to freezing. But you would still have to use a heater to keep the valve that opens to let water in from freezing.

The major downside of dry pipe sprinkler systems is that there is a delay between when the trigger is set off and when water starts flowing from the head.

The delay can have devastating effects since the fire can get out of control within seconds. However, this is counteracted by expelling the water at a higher pressure than in a wet pipe system.

Dry pipe sprinkler systems are rarely used but are common in unheated warehouses.

Variations of Dry Pipe Fire Sprinkler Systems

Dry pipe fire sprinkler systems have two variations: pre-action and deluge systems.

In a pre-action system, the triggering must happen twice before the water flows out of the sprinkler head.

First, a heat detector or smoke detector working independently from the head triggers the system, and water flows into the pipes. At this point, the system works like a wet pipe sprinkler system. The second trigger happens at each sprinkler head, making it release water into the fire.

Pre-action systems are ideal for minimizing false or accidental head activations. They are suitable in sensitive buildings like libraries and museums.

A deluge system works in the same way as a pre-action system. The smoke or heat detector works independently from the sprinkler heads. Triggering the detector causes water to flow in the pipes, but there is a manual mechanism that may be a cord or a button that you pull or push to activate the system fully.

The sprinkler heads of a deluge system do not have a trigger mechanism and are always open. They start working simultaneously when the system is activated fully.

You’ll find deluge fire sprinkler systems installed in chemical factories where a fire could spread fast and be potentially hazardous.

Why Do Fire Sprinkler Systems Use Water?

Fires are facilitated by three ingredients – fuel, oxygen, and heat. You can quickly and effectively extinguish a fire by removing one of these things.

Usually, water is ideal for removing heat because it comes out cold from the pipes. Also, water has a high specific heat capacity, enabling it to remove heat more efficiently during a fire.

Conclusion

A fire sprinkler system is an indispensable way to deal with fires in a building, be it residential or commercial. The sprinkler heads activate when there is a fire and pour cold water into the fire to extinguish it or suppress the heat and smoke as you wait for the fire department to arrive.

If you have a fire sprinkler system installed, we can help you prevent water damage if you accidentally set off your fire sprinkler.

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