All about residential 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. For a close-up view of a sprinkler, see how a fire sprinkler works.

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.   

The illustration to the right shows a sprinkler with a glass bulb 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 percent of of fires are handled by only one sprinkler. In the remaining cases, two sprinklers handled an additional four percent. It took three sprinklers to handle nearly all of the remaining 3 percent. 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 percent.

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 everything in the room 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 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.              

Sprinkler Facts

Sprinklers save lives.

Sprinklers are the most effective fire safety device ever invented.  Look at this comparison with smoke alarms and with no fire protection at all. The National Fire Protection Association reports that people with smoke alarms in their home have a 50 percent better chance of surviving a fire. Adding sprinklers and smoke alarms increases your chances of surviving a fire by over 97 percent.

Sprinklers save property.

Residential fire sprinklers are designed to save lives, but because they control fires so quickly, they also reduce property damage. Fire reports show that property damage is nine times lower in sprinklered homes.

Sprinklers are affordable.

Fire sprinklers add about one percent or less to the cost of a new home. This is about the same cost as upgrading carpeting. But carpets need to be replaced every ten years, while fire sprinklers last for the life of the home. Compared with the cost of carpeting, fire sprinklers give you peace of mind for a bargain price. Multipurpose systems that serve the sprinklers and plumbing with the same pipe may lower the cost even more.

Lifetime safety is lifetime quality.

The features of your home reflect your values and priorities. You select high-quality items for things that you want to last. Fire safety is a quality issue, too. Fire sprinklers will protect your family for the life of the home. You can ignore the issue and accept the minimum level of safety for your family and possessions, or you can build in quality fire protection for them.

Sprinkler Questions

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 action 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 10-15 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.                       

Shopping for a fire sprinkler contractor.

Fire sprinkler contractors should be listed in the Yellow Pages under "Fire Sprinklers," and they often advertise under "Sprinklers" as well. It is always better if you know someone who had sprinklers installed and can refer you to a contractor. If you are starting from scratch, though, a general caution is in order. Like any service, you will find contractors who are extremely competent and fair, and you will find those who are not necessarily so. Some states have contractor licensing laws to help weed out bad contractors. But not all states have such laws and their effectiveness in the states that do varies. Your best assurance is to get several bids and then diligently check opinions of past customers.

If you can, visit the homes of a contractor's past customers or a home that is under construction. If some sprinklers appear to be crooked instead of perpendicular to the ceiling or wall, or if there are gaps around the escutcheon plate (the metal trim ring around the sprinkler that covers the hole in the ceiling or wall), these indicate a sloppy installation and/or an inexperienced installer. Quality contractors pride themselves on sprinklers being perfectly straight and trim.

An important factor to consider is a contractor's experience with residential fire sprinklers. There is a critical difference between residential sprinklers and commercial types, and the last thing you want is someone installing the wrong ones. In some areas of the U. S., sprinklers are just getting introduced into single-family homes. If this is the case, even highly experienced contractors  may not be familiar with the residential type. Also, contractors with experience installing sprinklers in homes will treat the space like their home, taking extra care not to damage anything.

One way to check a contractor's experience is to ask what installation standard he uses. In the U. S., the correct standard for single family homes and duplexes is the National Fire Protection Association's  (NFPA) Standard 13D, usually referred to as NFPA 13D. This covers both site-built and manufactured homes. If they refer to NFPA 13 or 13R, keep shopping. Standard 13 governs sprinklers in non-residential structures and residential buildings higher than four stories. Standard 13R applies to multi-family residential (apartments, condos) up to four stories.

The edition of the standard is important, also. They are updated every few years to reflect the latest developments in new technology and efficiencies that reduce cost. The most recent edition of NFPA 13D is 1999, and a new revision should be available in late 2002. There is no valid reason for a contractor to be using an outdated edition.

Next to experience and competence, pricing is the next biggest issue. For a home with a standard floor plan (as opposed to a unique or complex layout) that is located in an area where several contractors are doing single-family work, prices can be expected to be under $1.00 per square foot of habitable space to slightly over $1.00. The lowest we have heard is 57 cents a square foot. If a home has a complex floor plan or unique features, the price may be higher because additional sprinkler might be needed to provide the proper coverage. If you want sprinklers in unheated spaces (garages, attics), the cost will be higher if that part of the system needs to be freeze protected (usually with approved antifreeze). The NFPA standards call for freeze protection in any area where the temperature is likely to drop below 40F.

Another factor affecting price is competition. In areas with a lot of  single-family sprinkler work, the costs are about one half that of areas with fewer installations (and thus fewer contractors who do this work). One caveat, though. If there is a lot of work but not enough contractors, they will tend to quote higher prices for new work because they already have all the jobs they can handle. 

Specialization is another factor. Contractors who specialize in single-family residential  work tend to be lower priced than other sprinkler contractors. For one thing, they have learned efficiencies that cut both installation time and materials. In a competitive environment, you can expect that they will pass these savings on to the customer in the form of lower bids.  For another, they have a lower overhead than contractors who do large commercial jobs. A high overhead can literally double the amount of a bid.

Lastly, prices will depend upon the prevailing labor rates in your area. If you live in an area with relatively high or low labor rates, then this will be reflected in bids on residential sprinklers. An exception might be a contractor who does his own work.

For a complete geographic list of sprinkler contractors, visit the RFSI member address of www.sprinklernet.org." (http://dbase.sprinklernet.org:591/members/index.html)

Copyright © Residential Fire Safety Institute, 2009.