Sprinkler Protection Simplified

October 10th, 2013

SprinklerProtectionHow much do you know about fire sprinkler systems? If you are a business or a building owner, an architect, or a member of the construction industry, you may be interested in some of these commonly asked questions on sprinkler protection. Explore with us sprinkler terminology, application and use of various types of sprinkler heads, issues arising from change in occupancy or change in use, solutions to common problems, and some simple ‘rules of thumb’ for preliminary assessments of sprinkler systems.

This article is aiming to provide a foundation for understanding sprinkler system design. And while there are many exceptions in the application of these systems, we are presenting answers to the more common and simplified scenarios to allow for a basic understanding.
Question: How do sprinklers work?
Answer: Sprinklers are activated by heat or (in rare cases) triggered remotely. However, the most common sprinkler head is heat-only activated, by which a small heat sensitive link fuses or glass bulb breaks at a specified critical pre-determined temperature (called link temperature) allowing the water to flow. Often the water flow is diverted with a deflector mounted directly in front of the orifice. Much research has been commissioned to optimize the sprinkler design for minimum water flow, diverter effectiveness, droplet size and drop momentum to enable specific kind of sprinkler applications.

There is a misconception that when a fire starts it will set off all the sprinklers in a room. This is not the case, except with the rare application of a deluge system. Every heat-activated sprinkler has an associated link temperature. When a fire occurs the heat from the fire rises to the ceiling and heats the sprinklers’ links or glass bulbs. When the link in the sprinkler head heats up and reaches this critical link temperature the sprinkler head opens (by link fusing or bulb breaking). The first sprinkler head to open is typically the one closest to the fire. Then (if under ideal conditions such as a flat ceiling, etc.) the sprinklers will open in a radial pattern from the source (fire) outward, as the heat at the ceiling opens up more and more sprinklers.

Question: Where can I find the guidelines to design and installation of a sprinkler system?
Answer: NFPA 13 provides the guidelines and requirements for design, installation, and maintenance of a sprinkler system. NFPA 13 is typically adopted “by reference”. In other words, when a fire and/or building code is adopted, that fire or building code will reference a specific edition of NFPA 13. This is how NFPA 13 is adopted into the codes. To view the latest edition of NFPA 13, you can visit NFPA’s website at nfpa.org.
Question: What is a design density?
Answer: The building is not designed to open up every sprinkler head in the building. As more sprinkler heads open, you lose water pressure in a building. This diminishing pressure results in a failure in the sprinkler system. Testing laboratories have conducted full-scale fire tests to provide criteria for different occupancies and hazards. A design density is comprised of two numbers:

  • Amount of water provided per square feet (gallons per minute/gpm per square feet) in the remote area
  • The size of the remote area. It is the maximum area in which the fire is controlled and/or extinguished based on testing

The above two factors dictate a design density. For example an office requires a light hazard design density (i.e. 0.1 gpm per sq foot over the most remote 1500 square feet). This means that tests have shown that if 0.1 gpm per square of sprinkler water is delivered over 1500 square feet, the fire can be controlled in an office until the fire department arrives and extinguishes the fire.

What does 1500 most remote area mean? The term remote area is referred as the hydraulically most remote area. It is basically the area furthest from the water source into the building. If a minimum of 0.1 gpm is provided in the area in the building that is hydraulically furthest from the water source (worst case area in the building), then the sprinkler system in the remainder of the building can produce at least 0.1gpm/sq ft or more in any other 1500 sq ft in the building. If the fire grows beyond the designed square footage, the gpm/sq ft (first number) will disintegrate to less than what is designed, which would most likely result in a failure of the sprinkler system.

Question: I have the design density information, but how can I compare it to what is required?
Answer: A quick and “dirty” but useful way of estimating or comparing design densities is to multiply the two numbers together. For example, if you are required in a warehouse to provide a design density of 0.495 gpm/sq.ft over the most remote 2000 square feet (i.e. 0.495/2000), but the building is capable of producing 0.6/3000. You can multiple the two numbers together to find out how many gallons per minute is produced in your remote area:

  • 0.495 gpm/sq ft x 2000 sq ft = 990 gpm
  • 0.6 gpm/sq ft x 3000 sq ft = 1800 gpm

In this case the existing building (design) density is more than what is the minimum density required. Therefore the building design density should be capable of providing the minimum required density of 0.495/2000.

Question: Are there different types of sprinkler system?
Answer: In the current edition of NFPA 13, there are 3 general types of sprinkler systems:

Control Mode Density Area (CMDA): Includes protection for storage and non-storage systems such as offices, manufacturing, retail, as well as some of the options for storage systems provide standard densities such as 0.495/2000 or 0.33/3000, etc. These densities are designed as worst case to control the fire (fuel load) to within the design area until the fire departments arrives and extinguishes the fire.

Early Suppression Fast Response (ESFR): Typically used for storage/ warehousing applications. These systems (instead of densities in terms of gallons per minute [gpm] per square foot over the most remote square feet) are calculated in terms of type of sprinkler head, 12 heads, calculated at a specific pressure. An example is K-25.2 ESFR 12 heads calculated @25 psi. This means that an ESFR with a K Factor of 25.2 is used. The 12 hydraulically most remote heads have been calculated to provide a minimum of 25 psi per head.

ESFR sprinklers (when designed correctly to the correct application/setting) are typically viewed as the premium types of sprinkler systems. This is because the sprinkler system itself extinguishes the fire without the need for fire fighters to enter a building to put out the fire, as opposed to other types of systems that only control a fire.

This is the reason why in most jurisdictions other system design “breaks” are given (e.g. smoke and heat vents are not required and hose demand is typically less) if the building is equipped with an ESFR system. The older ESFR systems used to require extremely high pressures (ranging from 50 psi to 90 psi), which in many cases would result in purchasing and maintaining a very expensive fire pump. These newer ESFR heads require lower pressures, in some cases as low as 15 psi, which makes the system more accessible to business/building owners. This is especially true in older municipalities where city water pressures are low.

For a better understanding of ESFR systems see the article “ESFR Sprinklers – The Perfect Solution To Warehouse Fire Protection?”

Control Mode Specific Application (CMSA): Typically used for storage/warehousing applications, these are newer heads that are typically viewed as a hybrid system between the standard CMDA and the ESFR system. Just like an ESFR, the system is calculated for certain type of sprinkler heads, with minimum number of heads operating at a given pressure. For example K-16.8 sprinklers, 15 heads calculated @22 psi is a typical example of a CMSA design criteria. Similarly it also allows for protection of commodities in buildings with higher ceilings without (in most cases) the need for in-rack sprinklers.

However these systems like CMDA are only designed to control the fire, not extinguish it. The “breaks” given when ESFR systems are used do not apply to CMSA systems. Given that the CMSA sprinkler heads are more expensive than a standard CMDA head, and yet there are no “breaks” given (e.g. smoke and heat vents are still required, etc.) as with ESFR, these type of sprinkler systems are not used as often as CMDA and ESFR systems.

Question: Are all sprinkler systems the same? If a building is sprinklered and its new usage has the same occupancy classification, can I just move in?
Answer: No. For example most laboratories are considered a ‘B-Occupancy’. Offices are also considered a B-Occupancy. However, the typical laboratory uses some amounts of flammable liquids. Therefore an Ordinary Hazard Group 2 (0.2/1500) is typically required versus a Light Hazard design density (0.1/1500) required for an office.
Question: If a previous tenant used a building for warehousing, why can’t another tenant move in since the use is the same? Shouldn’t the building be “grandfathered” in?
Answer: No. For example major renovations/upgrades may be necessary when a tenant moves out and another moves in. These major differences depend on the following:

  • Storage height
  • Ceiling height
  • Aisle width
  • Type of pallet used
  • Where the Commodity is Encapsulated (wrapped in plastic where more than 50% of the top is covered)
  • Cartoned or Uncartoned
  • Type of Commodity (e.g. metal, paper, plastic, etc.)
  • Area of storage
  • Method of Storage (rack, shelf, or floor/palletized)
  • Type of shelving (solid, grated, or open)

This is why every time a tenant moves in a warehouse, a new high piled storage permit is required. This permit ensures that the existing sprinkler system (as well as other existing protection systems) is adequate to meet water demand needed to control or extinguish a fire.

Question: What is a foam sprinkler protection system?
Answer: For specific high hazard applications, such as fuel tank farms, aircraft hangers, or protection of highly flammable liquids, a mixture of water and foam concentrate can be discharged from the sprinkler system. As expected these type of systems are more expensive than standard systems and require more maintenance. Installation of foam water sprinkler systems falls outside of NFPA 13 and is discussed in NFPA 16.
Question: I am told I have a dry pipe system. What is a dry pipe system?
Answer: Dry pipe systems are typically used in areas that are subject to freezing, are highly sensitive to water damage or of high-value. Examples include freezer food storages and outdoor canopies in cold climates, libraries, museums, and aircraft hangers. Because the piping is dry (contains air or nitrogen) and does not contain water until a fire occurs, it will take more time to ready the system due to filling the piping with water. This causes delays in the application of the sprinkler water to the fire, which results in a bigger fire. Therefore the design area for dry pipe systems are typically larger (by 30% based on NFPA 13). ‘Pre-action’ and ‘deluge’ systems are variations of the dry pipe system.

The combined dry pipe pre-action system requires two triggers before water is flowing through the pipes. At the first trigger, usually originating from a smoke or heat detector, the system will activate and the pipes will be pressurized with water. But no water is discharging out of the sprinkler heads yet, as a second trigger is required to expel water from the individual sprinkler heads. This second trigger signal needs to come from the heat of the fire, which in turn then will cause the heat sensitive link of the sprinkler head to break and open the sprinkler orifice (just as it is in the case with the common heat-only activated sprinkler system).

The sprinkler heads in a deluge system usually have an open orifice, and as a result require only a single remote trigger signal (by heat or smoke detector, or through manual activation). Because of this open orifice head design, all sprinkler heads are activated simultaneously in the event of a fire. These type of sprinkler systems are very rare and applied in high hazard scenarios, where rapid fire spread is of major concern. Deluge systems are installed in vaults, chemical plants, or high hazard areas where the spread of fire would be even more disastrous (e.g. storage of high hazard chemicals or explosives).

Question: What is an extended coverage head?
Answer: The extended coverage sprinklers allow for bigger/wider spacing than any of the other types of heads. For example for storage applications the standard sprinklers used in CMDA, ESFR, and CMSA range between 100-130 square feet of coverage per sprinkler head. In the case of the extended coverage heads the square footage can range between 144-196 square feet per sprinkler head.

The most important application when using extended coverage heads is based on the recent testing using the EC-25 sprinklers. EC-25 is a sprinkler head, which is a subcategory of the CMDA and CMSA sprinkler system in that it uses standard densities. What makes the system unique is that the application of the EC-25 allows for the use of solid shelving without the need for in-rack sprinklers (sprinklers installed in the middle of the racks).

ESFR and CMSA are not typically permitted to protect racks with solid shelving. With standard control mode sprinklers such as CMDA, solid shelving (if >20 sq ft) is allowed, as long as in-rack sprinklers are provided at every level or every other level (depending on the size of the solid shelving).

The only storage >12’ where gondola racks with solid shelving (>32 sq ft), as well as back-to-back shelf of uncartoned plastic commodities is allowed without the need for in-rack sprinkler, is when EC-25 sprinklers are used in accordance with the applicable sections of NFPA 13. This provides a great advantage to other types of sprinkler heads saving the expense and hassle of installing sprinklers in the middle of the racks.

Again there are very specific restrictions in NFPA 13 (ceiling heights, commodity types, aisles widths, etc.) to the use of these heads. Great caution (!) should be taken in the design and application of these type of sprinkler heads.

Question: Which is a better system?
Answer: There are no perfect systems that can be applied to all types of occupancy and uses. For example ESFR systems are typically viewed as the better systems for storage/warehouses. However, these systems have very narrow applications. For example racks with solid shelving cannot be used in a building with an ESFR system. The type of commodity you can store in a warehouse also depends on the type of ESFR sprinkler used.

For a better understanding of ESFR systems see the article “ESFR Sprinklers – The Perfect Solution To Warehouse Fire Protection?”

Question: I am required to provide a sprinkler system for my building but I am concerned about the water damage. What can I do?
Answer: In standard occupancies the majority of the damage in a fire is caused by smoke and not by water from the sprinkler system. Therefore the faster the sprinklers open and control or extinguish the fire the better a business can protect their commodities. For example, in many cases an ESFR system (though flowing more water) can extinguish a fire with only 2-3 sprinkler openings and as a result minimize the fire and smoke damage. This is the reason why many insurance companies give credit for the use of these types of systems.

In rare cases, when water cannot be used (e.g. computer rooms), alternative methods to sprinklers have been proposed and approved by most jurisdictions. These systems are more expensive than standard sprinklers. Other options include a combined dry pipe pre-action systems (again more expensive than the standard sprinkler systems) where two triggers (e.g. smoke detection and sprinkler link actuation) have to occur before water flows through the pipe and out of a sprinkler head. Water mist sprinkler technology may also be an option.

However, the reason for the popularity of a standard sprinkler system is its reliability and affordability when compared to other systems.

Final Considerations

Sprinkler systems are not only critical to property safety (buildings and content), but also to life safety (occupant and firefighter safety).

Though these systems are very reliable, proper maintenance by professionals is required, and NFPA 13 provides detailed guidelines on the maintenance of fire sprinkler systems.

NFPA 13 is a living and ever-changing document, as new testing and new technology is introduced every year. Therefore keeping abreast of the latest sprinkler protection designs and test results is paramount to ensure cost effective building and occupant protection over the life time of the building.

Disclaimer: The content presented is for general information purposes only and does not constitute advice. Readers should not act upon this article’s content or information without first seeking appropriate professional advice.