NFPA 13R Questions Addressed
by , from the 1/2005 issue of Sprinkler Age, page 38
The following interpretations were prepared by the Technical Services Department of the American Fire Sprinkler Association (AFSA) in answer to specific questions from contractors and/or Authorities Having Jurisdiction (AHJs). AFSA's informal interpretations are provided by AFSA Vice President of Engineering & Technical Services Roland Huggins, a P.E. registered in fire protection engineering; Phill Brown, S.E.T., C.F.P.S., a NICET IV certified automatic sprinkler technician; and J. Scott Mitchell, a P.E. registered in fire protection engineering. These opinions are provided for the benefit of the requesting party, and are provided with the understanding that AFSA assumes no liability for the opinions or actions taken on them.
Residential Corridor Density
QUESTION: You indicated you have a 4-story wood frame senior apartment protected by an NFPA 13R sprinkler system. Corridors that serve dwelling units are protected with residential sprinklers. You asked the following question, "Is a 4-head calculation at a density of 0.05 per the listing sufficient for the corridor? Or, must a 4-head corridor calculation be done at a density of 0.10 per section 188.8.131.52.2 of NFPA 13? Or, must a 5-head calculation be done per section 184.108.40.206.6 of NFPA 13 (openings protected)?"
ANSWER: In response to your question, we have reviewed NFPA 13R, 2002 edition, as the applicable standard. Our informal interpretation is that a 4-head calculation at a density of 0.05 per the listing is appropriate.
NFPA 13R:220.127.116.11 calls for the design discharge of sprinklers outside dwelling units to comply with NFPA 13. This alone would require a minimum density of 0.10 gpm/ft2 for any sprinkler outside the dwelling unit in an NFPA 13R system. However, 13R:18.104.22.168 allows the corridors to be protected with residential sprinklers and allows the design to be in accordance with the requirements for residential sprinklers.
This is clarified if we look back at these provisions in the 1999 edition of NFPA 13R, which puts it in an exception. 13R:2-5.2, like the 2002 edition, requires sprinklers outside dwelling units to meet the requirements of NFPA 13 for design discharge. Then exception #2 says that corridors..."shall be protected with residential sprinklers, with a maximum system demand of four sprinklers."
The intent remains unchanged in the 2002 edition, but is more clearly presented in the 1999 edition. The system design for residential sprinklers in corridors of NFPA 13R systems is to consist of hydraulically calculating four sprinklers at their listed flow and pressure as indicated in the product data sheets.
Residential and Extended Coverage Sprinklers
QUESTION: You asked the following questions, "When designing with residential sprinklers and there are instances of rooms that are better protected using extended coverage horizontal sidewall sprinklers, what is the correct design method? Should you calculate the four residential sprinklers and then prove the extended coverage horizontal sidewalls will provide a 0.10 density over the area of the affected room? Is this allowable per the intent of NFPA 13?"
ANSWER: In response to your questions, we have reviewed NFPA 13, 2002 edition, as the applicable standard. Our informal interpretation is that the residential design criteria are no longer applicable if other than residential sprinklers are used in the dwelling unit.
NFPA 13 does not address intermingled design methods such as this scenario where quick-response spray sprinklers and residential sprinklers are used in the same dwelling unit. Residential sprinklers and spray sprinklers are separate individual types of sprinklers and are tested using different test standards (UL1626 & UL199, respectively), thus the design cannot intermingle the two types. Each distinct area or room grouping must have its own design basis. For instance, if a hotel has an indoor pool area, the dwelling units with residential sprinklers could be designed based on the residential design method, while the swimming pool area could use the area/density or the room design method. These are larger, individual portions of the building in which you can meet the minimum size remote area for each type of sprinkler. If residential sprinklers are to be utilized in dwelling units, then they should be used throughout the dwelling unit, because there is no basis for design when they are mixed in such a small area. There are, however, certain exceptions that allow spray sprinklers to be used. For instance, in hot water heater closets where the ambient temperature is such that the temperature rating required is not available from any residential sprinkler line, spray sprinklers are permitted to be used. This is not a significant impact considering the small size of closets where the appliance is typically located and its separation from the other areas of the dwelling unit. A second exception is meeting the construction requirements for the room design method in the area with the spray sprinkler. Otherwise, NFPA 13 does not provide for calculating a single spray sprinkler. In closing, you cannot mix design methods in single small areas. Since this issue is not explicitly addressed, the AHJ must be consulted before proceeding.
QUESTION: You asked the following question, "Does the Ôactual coverage area' indicated in the manufacturer's literature for residential sprinklers become the Ôactual protected area' in 22.214.171.124.2 or is the area defined per the criteria in 126.96.36.199.2(2) via 188.8.131.52? If the residential sprinkler is located in a 12' x 12' room and 4' from two walls, what is the area of coverage corresponding to the application of the 0.10 density?"
ANSWER: In response to your question, we have reviewed NFPA 13, 2002 edition, as the applicable standard. Our informal interpretation is that the area of coverage for each sprinkler is determined either by the manufacturer's data sheet or by the criteria in 184.108.40.206, but not both. When treating the residential sprinkler as a spray sprinkler with regard to density, NFPA 13 does not address whether the other rules for spray sprinklers, such as the small room rule, are applicable.
When using residential sprinklers in a system that is to comply with NFPA 13, two criteria must be checked and satisfied. The first is to apply the 0.10 density to each sprinkler's area of coverage as determined by 13:220.127.116.11 and 18.104.22.168.2(2). The results of this application must then be compared to the resulting demand when applying the minimum pressure and flow requirements of the residential sprinkler's listing - see 13:22.214.171.124.2(1) - which equates to a lower density. The more demanding of the two is to be used in the hydraulic calculations for the sprinkler system. When determining the demand based on 13:126.96.36.199.2(2), the area of coverage given in the data sheet is not intended to be used. The area of coverage as determined by the SxL rules given in 13:188.8.131.52 is used. In some cases, the SxL rules may result in flows and pressures that are more demanding than the data sheet flows and pressures.
The technical committee has ruled that residential sprinklers must provide the same density as a standard spray sprinkler. Unfortunately the technical committee has not addressed whether other standard spray sprinkler criteria also apply to these residential sprinklers. Since it is being treated as a standard spray sprinkler in density, it is reasonable to apply all of the standard spray sprinkler rules to it. If standard spray sprinkler limitations for a standard upright or pendent are to be applied, then the sprinkler is only permitted to be spaced more than 71/2' from a single wall but not two. See 13:184.108.40.206.4. Since residential sprinklers are tested and listed based on a minimum density of 0.05 and spacing from 12'x12' to 20'x20' (6' to 10' from walls), one should be able to use them at those same spacings at a minimum density of 0.10. If the sprinklers can provide the wall wetting and meet the other requirements to be considered residential sprinklers at a minimum density of 0.05, then they should still be acceptable with an imposed minimum density of 0.10.
Since this position has not been addressed by the NFPA 13 technical committee, AHJ consent must be obtained before proceeding.
QUESTION: You indicated you are installing sprinkler systems in a 55-house subdivision. The supply arrangement is similar to Figure A-2-2(c) with a 1" supply pipe with a 1" meter located at the street. The meter has a shutoff valve connected to it. The piping splits in the crawl space of the house and the sprinklers and plumbing each have their own shutoff valve. There is no other shutoff valve, other than at the meter. You asked the following questions, "Does this arrangement fall under section 2-3, Multipurpose Piping System? Does the sign noted in 2-3(e) have to be installed? If so, where? Are we required to have another shut-off valve just prior to the split between domestic and sprinklers? Is it acceptable for lawn sprinklers to be fed off of the main 1" supply?"
ANSWER: In response to your questions, we have reviewed NFPA 13D, 1999 edition, which you indicated is the applicable standard. Our informal interpretation is that NFPA 13D is not clear on whether your system would be considered a "multipurpose piping system," but your arrangement should not require a sign to be installed.
13:1-3 defines a multipurpose piping system as, "A piping system within a dwelling unit and manufactured homes intended to serve both domestic and fire protection needs." There are two operative words in this definition. One word is "system." This word is singular which means that it is a single system, not two systems. The other word is "within" which means it is inside the dwelling unit, not outside. With these things in mind the type of system defined here is illustrated in Figure A-2-3(c). Unfortunately, Figure A-2-3(a) presents some confusion by labeling a two-system arrangement supplied by a single line from the public main as a multipurpose pipe system. Some contend that any arrangement where a single connection to the public water supply serves both the fire sprinkler system and domestic appliances, it would be considered a multipurpose piping system. This conflict was not addressed in the 2002 edition, but is expected to be clarified in the next edition.
Whether or not your system is considered to be a multipurpose piping system, the intent of NFPA 13D can be satisfied without installing a sign in the meter box at the control valve. What is the purpose of the valve? It is to inform anyone doing work on the system that a fire sprinkler system is supplied downstream and special considerations should be made. If a fire sprinkler system were not supplied downstream would the sign be required? No. If the system arrangement is as shown in Figure A-2-3(c) and a water softener is added, is the fire sprinkler system affected? Yes, therefore, the sign should be installed at the main control valve. If the system arrangement is as shown in Figure A-2-3(a) and a water softener is added, is the fire sprinkler system affected? Well, it depends on where the water softener is located. If it is located in the main line before the split, the sprinkler system is affected. If it is located on the domestic side of the split, the sprinkler system is not affected. So, one could argue that if the arrangement is such that a water softener or other device that restricts flow and pressure cannot be installed, a sign should not be necessary.
In your arrangement, where the single line splits in the crawl space - one side to the fire sprinkler system and the other side to the domestic appliances, any water softener or other device to be installed in-line would be installed on the domestic side. It would have no impact on the fire sprinkler system. Therefore, a sign would not be necessary and should not be required.
Since this seems to be a confusing issue within NFPA 13D and considering that the issue is expected to be addressed in the next edition, it would be reasonable for the AHJ to allow omission of the sign, or at least allow a sign with smaller letters so that it can physically fit in the meter box. As with any ambiguous issue, AHJ concurrence must be obtained before proceeding.
EDITOR'S NOTE: As noted in the introduction, these informal interpretations were prepared by AFSA's Technical Services Department. These opinions are provided for the benefit of the requesting party, and are provided with the understanding that AFSA assumes no liability for these opinions or actions taken on them. When appropriate and time permits, informal input from the AFSA representative on the applicable NFPA committees will be included. These opinions have not been processed as "formal interpretations" by NFPA and should not be considered, nor relied upon, as the official position of NFPA or its committees.
AFSA's informal interpretations are provided by AFSA Vice President of Engineering & Technical Services Roland Huggins, a P.E. registered in fire protection engineering; Phill Brown, S.E.T., C.F.P.S., a NICET IV certified automatic sprinkler technician; and J. Scott Mitchell, a P.E. registered in fire protection engineering. These opinions are provided for the benefit of the requesting party, and are provided with the understanding that AFSA assumes no liability for the opinions or actions taken on them.