Fire Sprinklers

You never know when or where a fire will start in your home. What if you could have a firefighter stationed in every room 24 hours a day, ready to stop a fire the minute it broke out? That is what fire sprinklers are-instant firefighters. They are installed in the ceiling or high on a wall and are attached to the same water supply that feeds your home's plumbing fixtures. Residential fire sprinklers are small. In fact, they fit in so well that you have to point them out for people to notice them.

You already have water running throughout your home to sinks, showers, toilets and washing machines. Fire sprinklers use the same water to extinguish a fire. Average-sized rooms only need one sprinkler.

A sprinkler is similar to a hose nozzle because it breaks the stream of water into a fine spray. The sprinkler does not release the water until it is heated by a fire. A tight metal seal over the waterway holds the water back. The cap is held in place by either a glass bulb or metal link. Both are very rugged but are designed to melt in the high heat of a fire.

For example, when a sprinkler with a glass bulb is over a fire in a wastebasket, the fire consumes the oxygen in the surrounding air. The burning creates a narrow plume of smoke and hot gases (e.g., carbon dioxide and unburned carbon monoxide) that rise to the ceiling. When the hot gases reach the ceiling, the heat plume begins to spread out toward the walls. When the hot gases reach the nearest sprinkler, they will heat the fusible element that holds the cap in place. The cap will fall away and the sprinkler will spray water on the fire. Because the water immediately cools the hot fire gases in the plume, the other sprinklers won't open because there is not enough heat to melt their fusible element.

In a small number of fires, the burning material produces too much heat for the nearest sprinkler to handle. The adjacent sprinklers then act as backups. If the fire is so hot that the water from one sprinkler cannot cool it, the hot gases will reach the next nearest sprinkler. Then that sprinkler will open to stop the fire. This design of opening only when there is enough heat limits the number of sprinklers to what is needed to stop the fire. Fire records show that 93% of fires are handled by only one sprinkler. In the remaining cases, two sprinklers handled an additional four %. It took three sprinklers to handle nearly all of the remaining 3%. Keep in mind that these figures include large warehouses storing highly combustible goods that generate tremendous heat. In these cases, more than one sprinkler may be necessary to spray enough water to stop the fire. In homes and apartments, it is rare to have more than one sprinkler operate, so the number of fires controlled by one sprinkler in residences is nearly 100%.

By cooling the fire gases rising from the fire, the sprinkler prevents the fire from reaching the flashover stage. Flashover is a dangerous point in a fire where the unburned carbon monoxide in the gas layer reaches its autoignition temperature and breaks into flame. This occurs after the gas layer has spread to the walls and begun to bank down toward the floor. The radiant heat from flashover ignites all of the combustible items in the room at once, pushing heat and smoke into other rooms.

Once the water from the sprinkler has stopped flashover, the spray will begin reaching the burning material and cooling it to below its combustion temperature. Then it can no longer burn and the fire goes out. Responding firefighters will shut off the sprinkler once they are sure that the fire is completely out.

Information provided by the Residential Fire Safety Institute website.

FAQs

Will sprinklers leak?

Sprinklers and their piping are pressure-tested at two to three times higher than your plumbing system, even though they use the same pressure as your plumbing. Therefore, the chance of a leaking sprinkler is practically nil. Like your plumbing pipes, sprinkler pipes are not exposed to cold areas so they are protected from freezing. They do not leak because, unlike faucets and other fixtures that are operated often throughout their lives, fire sprinklers remain closed until needed and thus do not receive the wear and tear of daily use.

Won't all the sprinklers in the room go off at the same time?

As the graphic above explains, the heat from a fire will open the nearest sprinkler. Its water cools the hot fire gases, making it impossible to open other sprinklers. Thus, in nearly all cases there is not enough heat to open the next nearest sprinkler. In the rare case that the heat is too much for the nearest sprinkler, the next nearest sprinkler will open to overcome the fire. The operation of more than one sprinkler occurs in a small percentage of commercial buildings, but is very unlikely in homes. Thus, only the sprinklers necessary to stop the fire will operate, and fire records show that it usually takes just one.

Why, then, do people think that all of the sprinklers in the room go off at the same time? There are two reasons. First, Hollywood gag writers show all of them going off for comic effect. They have shown this happening from someone merely lighting a cigar or pulling a fire alarm switch. Those actions cannot even make one sprinkler open, let alone all of them.

The second reason is that a lot of people mistakenly think that smoke will open a sprinkler. They have seen smoke spread throughout a room, so they conclude that smoke affect all of the sprinklers in the room. But once people understand that:

Only heat can open a sprinkler (smoke can't melt metal or burst glass) and,
Only a threatening fire can generate enough heat to open a sprinkler, then they understand that all of the sprinklers won't open at the same time, even in a smoky room.

Aren't they unsightly?

Residential fire sprinklers are much smaller than ones that you see in stores and offices. All residential models come in colors to match popular ceiling and wall colors, and manufacturers will even custom-paint them for you. Many models are partially recessed into the ceiling, and only 1/4"-3/4" is below the ceiling. If you want them completely recessed, these models are also available. The fully recessed models are hidden by a cover plate that is painted to match the ceiling. The cover is held in place by a metallic link that melts in a fire and exposes the sprinkler.

It is common to find that visitors do not notice the sprinklers at all unless you point them out, even the ones that are not recessed into the ceiling.

Won't the water create more damage than the fire?

One of the myths about sprinklers is that they will cause water damage. While this may seem logical (after all, they spray water), fire records show that the reverse is actually true. Here is why. A residential fire sprinkler sprays about only 10-18 gallons of water per minute and operates early in a fire to stop the burning. A hose used by firefighters flows ten times that amount, 175-200 gallons a minute. If sprinklers are not present, fires typically burn for an additional 10 to 15 minutes until firefighters arrive and begin spraying it with their hoses. Two things happen to cause more damage than sprinkler. First, more of your possessions have burned up before the firefighters intervened, and then you have 10 times more water being sprayed on what is left at a very high pressure.

The combination of the sprinkler's quick response, the smaller water flow and lower pressure significantly reduce water and property damage. Think about it. What is more damaged, a sofa that can de dried off (sprinklered fire) or one that has turned to ashes (manual suppression)? How about an oil painting that was protected by a fine spray (sprinklered fire) or one where all that was left was part of a frame (manual suppression)? Without sprinklers, the heat and smoke from a fire travel very quickly, damaging the furniture and possessions throughout the house. With sprinklers, the sprinkler nearest the fire will stop it before it can develop the damaging heat and smoke.

You can install an alarm to alert you when a sprinkler opens and water starts flowing. The alarm will also alert neighbors, and you can have it monitored by an alarm company so they can call the fire department if no one is around.

Can I install them myself?

Only qualified contractors should install fire sprinklers. They will know how to install the system in compliance with national standards, which ensures that the spacing is correct and an adequate water supply is available. Also, fire sprinklers have different operating temperatures and flow patterns. You need someone knowledgeable who can select the correct sprinkler for each area of the home.

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