Specifying fire sprinkler systems

Specifying engineers can add value and clarification to the installation process for a sprinkler system.

07/12/2011


Figure 1: Good fire sprinkler system specifications include information on the type of construction, acceptable or unacceptable types of pipe and sprinklers, and materials in the environment that might be incompatible with material selections. Courtesy: TSpecifications for fire sprinkler systems are the written descriptions of the needs, desires, and concerns of the building owner with respect to the use of its building and how the sprinkler system needs to perform. In the ideal situation, specifications are written by an engineer after meeting with the building owner, upon understanding how the owner is going to use the building and what will be put into the building. Recognizing that not all situations are ideal, the specifying engineer needs to have sufficient information in order to completely understand the use of the building so that information can be transferred to the trades to interpret the specifications.

An engineer can add value to a construction project and can significantly help a sprinkler contractor understand the design intent. Clear, concise, and complete specifications identify appropriate criteria for the design and installation of the system prior to the development of shop drawings.

Broad, all-encompassing statements are not particularly helpful in fire sprinkler system specifications. Building owners want to comply with all of the laws that apply, so a specification that reads “The sprinkler system must comply with all applicable codes and standards” doesn’t describe how the sprinkler system needs to perform. Some fire sprinkler system specifications consist almost entirely of these kinds of statements and lack the material the fire sprinkler contractor needs.

The decision as to whether specifications will include drawings showing sprinkler system equipment placement and locations is controversial. The National Council of Examiners for Engineering and Surveying (NCEES) has a position statement that requires contract documents for fire protection systems to include a set of drawings sealed by a licensed professional engineer. (See PS 23 in the NCEES Manual of Policy and Position Statements, August 2010.) Some state and local jurisdictions have interpreted this to mean that the drawings need to be included in the specifications, but this is not a universal interpretation.

The Society of Fire Protection Engineers (SFPE), the National Society of Professional Engineers (NSPE), and the National Fire Sprinkler Assn. (NFSA) each have reached different conclusions regarding the subject of drawings as a part of the specifications. Each of these organizations agrees with some variation of the idea that the specifications do not need to include specific locations of sprinklers and pipes, although they can include drawings indicating which portions of a building will be protected with sprinklers using notes or symbols. The exact placement of sprinklers and pipes is developed by a sprinkler contractor in the form of shop drawings, which can be reviewed by the specifying engineer for agreement with the design concepts. These shop drawings become part of the overall contract drawings and fulfill the concerns about engineering oversight.

So, if the specifications are not supposed to be limited to general quotes of applicable codes and standards, and they are not supposed to be sets of building plans showing equipment placement, what should they include? The short answer is that they need to include the following:

  • The needs, wishes, and desires of the building owner
  • The performance objectives of the sprinkler system
  • Guidance for the contractor on any issue that requires engineering judgment.

Needs of the owner

If the owner has specific needs or desires regarding the aesthetics of the sprinkler system installation, such as a desire to eliminate exposed pipe or a need to have a sprinkler with a certain type of finish, the specifications need to convey this information to the sprinkler contractor.

As a representative of the owner, the specifying engineer is in a position to understand how the owner is going to use the building and what will be in it. As such, the specifying engineer is in the best position to determine details like the commodity classification for storage and the hazard classification for the sprinkler system.

To help represent the needs, desires, and concerns of the building owner, and to convey information to the sprinkler contractor, NFPA 13: Standard for the Installation of Sprinkler Systems requires the owner to fill out an owner’s certificate. As the agent of the owner, the specifying engineer will most frequently complete the certificate and convey it to the sprinkler contractor in the specifications.

Performance objectives

The sprinkler system’s performance objectives also need clarification in the specifications. NFPA 13 indicates that sprinkler systems can control or suppress fires, but it does not express a preference. If the building owner desires a sprinkler system that will suppress the fire, this needs to be communicated to the sprinkler contractor in the specifications. If suppression is desired, the specifying engineer must coordinate all of the other aspects of building design to work with the suppression-oriented sprinklers in order for the sprinkler contractor to be able to provide a system that meets all of the codes.

Another feature found in some sprinkler systems is a water curtain or an exposure protection system to protect an object or structure. The NFPA standards may not identify design criteria of such systems because the goal is different in each case. Potential goals in such circumstances include:

  • Cooling the object and keeping it from exploding
  • Putting out a fire surrounding the object
  • Protecting the structural members (beams, columns, trusses, etc.) of the building for the duration of a fire
  • Providing for short-term life safety while people evacuate the area
  • Preventing a fire from moving from one structure to the surface of another structure
  • Preventing a fire from moving from one structure into another structure through a door or window
  • Preventing smoke and/or heat from moving from one part of the structure to another part of the same structure.

An engineer does not convey sufficient information to the contractor by saying, “Provide a water curtain in accordance with NFPA 13.” The specifying engineer should determine and identify discharge criteria for the sprinklers in these situations as well as any other criteria not directly covered in the applicable NFPA standards or needing engineering judgment in application from NFPA standards.

A similar situation exists with NFPA 30: Flammable and Combustible Liquids Code and the protection of flammable and combustible liquids. Small portable containers of these liquids can be protected with fire sprinklers in accordance with well-established tables and figures. Engineering judgment is not needed for protection of common storage arrangements of known liquids as long as they are well defined and in one of the tables in NFPA 30.

For larger tanks, there are no direct sprinkler or water spray protection criteria in NFPA 30. Instead, Section 21.6.3 of the 2008 Edition of NFPA 30 states that for larger tank protection, “fire prevention and control provided for tank storage facilities shall be determined by an engineering evaluation of the installation and operation, followed by the application of sound fire protection and process engineering principles.” So a blanket statement in a specification that requires a large tank to be “protected with a water spray system in accordance with NFPA 30” is not sufficient.

Codes and standards

The specifications do need to identify the codes and standards that apply. While this is important for all types of occupancies, it is particularly important for residential occupancies that are four stories or less in height because there are two NFPA standards that cover this type of occupancy in their scope: NFPA 13 and NFPA 13R: Standard for the Installation of Sprinkler Systems in Residential Occupancies Up to and Including Four Stories in Height. But these two standards have very different performance objectives. It would be a problem if a specifying engineer had one set of objectives as a design concept while the other standard was used by the contractor with a different set of objectives.

Just because the building fits the criteria for allowing the use of NFPA 13R doesn’t mean that it is necessarily the option that best suits the building owner. If the code application strategy is to take advantage of alternatives to building code requirements, such as area increases or elimination of draft stops in attics, an NFPA 13 system might be required, even if the building is residential and only three or four stories in height. From an insurance perspective, an NFPA 13 system might result in lower insurance premiums for the owner, so the specifying engineer needs to consider these options and clarify its decision in the specifications.

The specifications need to address the resolution of conflicts between the codes and the standards. Most codes have a statement that says when a referenced standard conflicts with a code, the code takes precedence. But is that in the best interest of the client?

For example, consider a six-story apartment building being constructed in accordance with NFPA 5000: Building Construction and Safety Code. NFPA 5000 references NFPA 13: Standard for the Installation of Sprinkler Systems in Residential Occupancies Up to and Including Four Stories in Height, as the applicable installation standard for the sprinkler system in such a building. However, Section 25.3.5.4(1) of NFPA 5000 permits sprinklers to be omitted from closets that are less than 12 sq ft. NFPA 13 does not permit sprinklers to be omitted from closets in apartment buildings.

In this conflict between NFPA 5000 and NFPA 13, the code trumps the standard—sprinklers are not required to be installed in closets that meet the criteria of NFPA 5000, 25.3.5.4(1). But is that in the best interest of the client? What if the owner can get better insurance discounts for a sprinkler system that includes sprinklers in the closets? Even though they are not required, the specifying engineer might add some value to the process by specifying sprinklers for the closets, potentially saving the owner money in the long run.

Types of systems and components

Figure 2: Fire sprinklers are available in a wide range of styles, finishes, and colors. Courtesy: The Viking Corp.Given the information in the specifications on how the building is being used, a sprinkler contractor can make basic decisions on the type of sprinkler system to install and what components to use to put that system together. But the specifying engineer does need to consider the special situation of the building and provide input to those decisions in the best interest of his or her client. The following questions may need to be answered in the specifications if there are special situations that would make the sprinkler system better fit the use of the building:

  • Is the owner better served by a wet, dry, preaction, or deluge system?
  • If a preaction system is being used, should it be single-interlock, double-interlock, or non-interlock?
  • In areas subject to freezing, is a dry, preaction, or antifreeze system going to be the right choice?
  • Can combinations of the piping with other building systems (mechanical or domestic) make the sprinkler system more efficient?
  • Is the owner better off with a certain type of sprinklers?
  • Will the environment be a concern for corrosion (inside the pipe or outside the system)? If yes, what sprinklers, pipe, valves, and hangers need to be selected or what type of protection will be provided?
  • Does the owner want to have the ability to monitor the pipe for internal corrosion?
  • Should air release mechanisms be provided to limit potential future internal system corrosion?
  • Is the owner better off with a certain type of pipe?
  • Will materials be present that will be incompatible with a type of pipe material?
  • Are there components that the owner wants the contractor to use or does not want the contractor to use for some reason?
  • Is the specific placement of system components and equipment important to the owner?

For example, consider a dry-pipe sprinkler system being installed in an attic. NFPA 13 permits many different types of piping materials to be used, including ungalvanized steel, galvanized steel, and specially listed threaded thinwall pipe. Each of these different piping materials has a different cost associated with it and a different life expectancy depending on the water supply and the environment. The specifying engineer can weigh the costs of the options against the expected benefits in hydraulic efficiency and life expectancy and make a recommendation if one or more of the options are undesirable to the building owner or better for the building owner. In the absence of any information in the specifications, many contractors will select the option that provides the lowest total cost of installation without considering the service life of the system.

Earthquake protection

Sprinkler systems need to be able to survive seismic events to help control fires after earthquakes. Specifying engineers should write detailed specifications that include whether the building code requires seismic protection for the sprinkler system. An example of a poorly written section in a sprinkler system specification is “Earthquake bracing shall be provided in accordance with NFPA 13.” This is poorly written because there is more to protecting a sprinkler system during an earthquake than just bracing. NFPA 13 requires three different types of protection: bracing, flexibility, and restraint. By mentioning only bracing in the specifications, it could be interpreted that flexibility and restraint do not need to be addressed, when in fact these are critical items to assure that a sprinkler system survives a seismic event.

Another reason the statement it poorly written is that it does not indicate that protection is required. The implication of the sentence is that NFPA 13 will provide the information as to what buildings need seismic protection for the sprinkler system. But NFPA 13 does not provide that information. Instead, NFPA 13 just tells the users how to help the sprinkler system survive an earthquake if some other code, standard, or specification requires that kind of protection for the system.

Rather than making a blanket statement and leaving it to the sprinkler contractor to investigate, the specifying engineer should clarify whether the sprinkler system in the building is going to need protection from earthquake activity. If the building and the sprinkler system are going to need earthquake protection, then the specifying engineer can determine the variables necessary to calculate the seismic load factor, including the soil conditions for the ground on which the building is going to be constructed. With all of this information in the specifications, the sprinkler contractor can determine adequate brace materials and locations.

Sprinkler location and position

Regardless of where his or her jurisdiction falls, there are a few ways that a specifying engineer can provide valuable input to the decision-making process regarding the location and positioning of sprinklers and adding value.

The first option in adding value to the process is to identify the areas in the building where sprinklers will not need to be installed. This situation sometimes calls for engineering judgment, or for information that is outside the sprinkler contractor’s area of expertise. For example, NFPA 13 permits sprinklers to be omitted from certain locations in elevator shafts when noncombustible hydraulic fluid is being used. The sprinkler contractor won’t always know whether the elevator is hydraulic, or what kind of fluid is being used, but the specifying engineer should be able to obtain this information and convey it to the contractor in the specifications.

In addition, NFPA 13 and NFPA 13R permit select spaces to be unsprinklered (certain types of concealed spaces, electrical rooms, closets, bathrooms, etc.), but is it in the best interest of the building owner to leave sprinklers out of these spaces? In some cases, the decision to omit sprinklers will increase the demands of the water supply, causing a 3,000-sq-ft design area instead of a 1,500-sq-ft or a 900-sq-ft design area.

Regarding sprinklers on balconies and decks, the specifying engineer can also clarify how to handle a conflict between NFPA 13R and the International Building Code and International Fire Code (IBC/IFC). While NFPA 13R does not require any balconies or decks to be protected with sprinklers, the IBC/IFC does require sprinklers on certain decks of buildings of a certain type of construction. The specifying engineer can sort through the conflict and clarify whether sprinklers need to be used to protect the balcony on the specific building.

The second issue regarding sprinkler placement and location is analyzing unusual ceiling configurations with different elevations at the ceiling and ceiling pockets. NFPA 13 has some general rules that provide guidance on how to deal with common situations, but when the ceiling configuration or ceiling pocket does not conform to the general rules in NFPA 13, the specifying engineer can provide more value by performing calculations and determining where sprinklers are best located.

For example, consider a room with a ceiling pocket that is 6 ft long, 6 ft wide, and 4 ft deep. The pocket is only 144 cu ft in size, but do sprinklers need to be installed up in the pocket? The pocket does not conform to the skylight rules of section 8.5.7 in NFPA 13 because the area is greater than 32 sq ft. The pocket does not conform to the ceiling pocket exemption of section 8.6.7 of NFPA 13 because the depth exceeds 3 ft.

Section 8.1.1(6) of NFPA 13 states, “Clearances between sprinklers and ceilings exceeding the maximums specified in this standard shall be permitted, provided that tests or calculations demonstrate comparable sensitivity and performance of the sprinklers to those installed in conformance with these sections.” This section permits sprinklers to be omitted from any pocket provided calculations show the sensitivity and activation of sprinklers at the lower ceiling elevation would be comparable to other arrangements permitted by NFPA 13. A specifying engineer could perform such calculations to show comparable performance, thereby adding value to his services for the building owner.

Speculative buildings

Buildings that are constructed without any specific use in mind present various challenges for fire sprinkler protection. Without directions in the specifications, a sprinkler contractor will not be able to provide a sprinkler system with the flexibility to meet eventual occupant demands without significantly reworking the sprinkler system.

The best way to represent a building owner who is constructing a speculative building is to provide information in the specifications that allows for flexibility. Considering worst-case anticipated scenarios, using reduced sprinkler spacing and providing a significant water supply will help a building owner to allow multiple uses without significant modification to the originally installed system.

Water supplies

The specifying engineer needs to have some knowledge of the water supply demand for the sprinkler system. If the system is not completely laid out and calculated in the specifications, a specifying engineer can estimate the sprinkler system flow demand by taking the flow necessary for the remote sprinkler, multiplying by the number of sprinklers in the design area, adding additional flow for “overage” (the additional flow from sprinklers closer to the water supply), and adding the hose demand for the sprinkler system.

The pressure demand is harder to estimate, but it can be figured by adding the end pressure necessary at the most remote sprinkler to the elevation losses and a reasonable estimate of the friction losses. Friction losses can be estimated by using a reasonable average friction loss per foot of pipe and multiplying it by the total number of feet of pipe from the water supply to the most remote sprinkler assuming a reasonable routing of pipe.

Once the specifying engineer has a reasonable estimate of the sprinkler system’s demand, he can look at the water supply to make sure that it will be sufficient. When analyzing the water supply data, it is important to apply reasonable safety factors for daily and seasonal fluctuation of the water supply. The specifying engineer can determine which reasonable safety factors need to be applied. The specifications need to include the water supply information and an indication that a safety factor has been applied so that the sprinkler contractor and authorities having jurisdiction do not apply additional safety factors.

Once the demand is estimated and the water supply has been analyzed, the engineer can decide whether a pump will be needed for the project. A pump can be used if the water supply does not have sufficient pressure, but if the water supply does not have sufficient flow, a pump by itself will not solve the problem. If the water supply does not have sufficient flow for the sprinkler system, an alternate or additional water source will need to be provided.

Another question that needs to be answered with respect to water supplies is whether there is reason to suspect that the water supply will cause unusual corrosion or microbiologically influenced corrosion (MIC). The specifying engineer can act as the owner’s agent and analyze the water supply to determine if there is reason to believe that unusual corrosion or MIC will result if the water supply is used in the sprinkler system. If there is reason to believe this will happen, the specifying engineer needs to develop an approach to address the issue and include this information in the specifications.

Engineering judgment

As a function of the engineering licensing laws in most jurisdictions, only licensed engineers are permitted to perform the process of design. In most cases, the act of preparing the specifications is the extent of the design of the fire sprinkler system. The development of shop drawings by a technician to show the system layout in accordance with the engineer’s design as described in the specifications is not considered to be the design of a sprinkler system. Note that this is consistent with the joint position statement issued by SFPE, NSPE, and the National Institute for Certification in Engineering Technology in July of 2008.

The specifying engineer then often has the responsibility to review and verify that the shop drawings meet the design intent as described in the specifications. Another way of presenting this concept is to say that the engineer is involved in the aspects of system planning that require engineering judgment, and the technician is involved in aspects of system planning using criteria from NFPA (or other) standards that show conformance with, and use guidance from, the engineering concepts in the engineer’s design.

Since the specifying engineer may be the engineer of record, he or she needs to answer all of the questions that require the use of engineering judgment in the design of the sprinkler system. At the very least, specifying engineers should be making the decisions on the hazard classification of building areas and/or commodities being stored in the building, analyzing the water supply, and determining whether the mechanical systems in the building (including the fire sprinkler system) will need to have seismic protection. Other aspects of engineering judgment may also be important to other special situations.

Summary

The specifying engineer is required to be competent and knowledgeable in the design of fire sprinkler systems. Without addressing the questions asked, a sprinkler contractor cannot provide an adequate fire sprinkler system that will allow the building owner appropriate use of the building.

The specifying engineer can best serve his or her client by addressing issues related to codes and standards, design objectives/intent, hazard classifications, commodity classifications, materials, water supplies, and unsprinklered spaces. The specifying engineer should consider aspects of planning a sprinkler system that require engineering judgment to be applied.

If specifications provide the appropriate information, the sprinkler contractor will have a much easier time installing a sprinkler system that allows the building owner to use the building in the intended manner. By correctly representing the needs of the owner, the specifying engineer can add value to the process of getting a sprinkler system installed in a building and can save clients a significant amount of money during the life of the building.

Isman is the vice president of engineering for the National Fire Sprinkler Assn. Isman represents the fire sprinkler industry on 12 technical committees of the NFPA.



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