Summary: Frequently asked questions concerning NFPA code compliance and fire protection systems are covered in this blog. With citations to pertinent NFPA sections, it discusses sprinkler placement for certain scenarios, including walk-in freezers and back-to-back arrangements. There is no set answer to the question, “How long can a fire pump take to start?”; it activates when pressure lowers. Backup power should ideally step in after a primary power outage in ten seconds.

The blog makes clear that, in sprinkler systems, NFPA 13 typically permits the combination of insulation and antifreeze for freeze protection. Additionally, it considers modifying current systems to add more antifreeze than the UL recommends. Under some circumstances, and with the authority having jurisdiction’s (AHJ) permission, this might be allowed.

With concise explanations based on the pertinent NFPA code sections, the blog delves into particular situations like sprinkler regulations for mosque minarets and baffle obstacles in warehouses. All things considered, this blog is a useful tool for knowing the rules governing fire safety systems and making sure they are followed.

1. Sprinklers Above Freezers. Description- The 2010 NFPA 13 edition is being followed in the sprinkler protection of a project. Walk-in freezers with dry sprinkler protection are part of this facility. Question 1. Are sprinklers needed over the top of these refrigerators since the floor area is protected?

Answer: Sprinklers do, in fact, need to be installed over the freezers. Check out NFPA 13’s 2010 edition’s Section 8.15.22 (and associated subsections). The need for sprinklers to extend into the adjacent space by 0.6 times the square root of the sprinkler system’s design area is described in Section For a further example of the design arrangement, see Figure A.

2. ESFR Obstructions in Ordinary Hazard. Description- The occupation of a current ESFR warehouse is being converted to ordinary hazard group I. The ESFR sprinkler heads are something the owner would rather leave in situ. Ten feet beneath the ESFR sprinkler heads, though, they intend to install a 2-foot-wide duct line. Question 2. Is there any relief in the 2016 code that prohibits sprinkler heads (as NFPA 13 2022 does) behind this duct work? Or would the duct still need to be situated two feet from the side of the ESFR sprinkler head(s)?

Answer: Even in cases of protected light and conventional danger occupancies, the spacing and obstruction standards for the ESFR sprinklers remain applicable, according to the specifications in the 2016 edition of NFPA 13.

The chapter 10 provision to apply the spray sprinkler spacing and obstruction criteria was not included until the 2022 version. That being stated, it is not unusual for an AHJ to approve the use of the most recent version of NFPA 13, particularly in cases where the adopted edition lacked the particular requirements at issue. The obstruction mentioned can be avoided if the AHJ gives its approval to apply the 2022 criterion.

3. Extended Coverage Sidewall Sprinklers Installed Back-to-Back. Description- This subject concerns whether, with a certain kind of barrier between them, fire sprinklers on opposing walls can be placed near each other. Whether the barrier satisfies size criteria will determine the response. Question 3. Is it possible to install extended coverage sidewall sprinklers back-to-back with a baffle in compliance with Section 11.3.4? A baffle this way would have to be eight inches long and six inches wide.

Answer: Not really. A baffle installed in accordance with Section is not continuous, as Section requires, in our view. This part mandates that a “continuous lintel, soffit, or baffle” must divide back-to-back Extended Coverage sprinkler installations.

Recall that the continuous baffle, soffit, or lintel serves two purposes. The soffit, or baffle, makes sure the sprinkler closest to the fire runs and that sprinklers on both sides don’t run at the same time. For instance, the sprinkler on the opposite side of the partition (spraying away from the fire) shouldn’t work if a fire breaks out on one side. This would merely divert attention away from the required sprinkler and be of no use. Furthermore, sidewall sprinklers are intended to release some of their spray behind the sprinkler, hence, in the absence of a separation, one sprinkler discharging could result in the cold soldering of the sprinkler next to it. Obviously, the fire may not be contained if the sprinkler facing the fire area is not working because of the spray from the sprinkler next to it.

Considering the aforementioned, a basic baffle in compliance with would not be enough to capture the heat and guarantee that the right sidewall sprinkler turns on. In our view, the back-to-back sprinklers should be put tight to the ceiling and separated continuously (across the bay) to capture the heat from a fire.

Finally, it should be mentioned that section for regular spray sidewall sprinklers does require that the spacing between back-to-back sidewalls project a minimum of 4 in. (below the deflector), even if it is not covered in the extended coverage chapter (Chapter 11).

4. QR Area Reduction and Room Design in FM. Description- This issue inquires whether FM Global, a business insurance carrier, accepts certain techniques for estimating fire sprinkler system water requirements: room-by-room or a smaller area for faster-reacting sprinklers. Question 4. Does FM allow the room design method or the Quick Response Area Reduction for hydraulic calculations?

Answer: No, quick response sprinkler design area is not included in Factory Mutual (FM) data sheets.

Reduction and/or the NFPA 13 room design approach. FM Radio Non-storage occupancy data sheet 3-26 Table 2 and Section for an HC-1 sprinkler system with wet pipes does offer note 1, which states that, if fire compartmentation with a minimum one-hour fire rating is present, the demand area for dormitories, residential, and dwelling type areas may be based on the largest room area, but not fewer than four sprinklers.

5. Water Tank Critical Levels. Description- According to Section 14.9 of the 2023 version of NFPA 22, sensors for two crucial water temperatures, levels, and pressure readings are required for pressure tanks. Question 5. What are the crucial levels?

Answer: Section 14.9.2 identifies the important thresholds mentioned in Section 14.9.1, including:

Critical water temperatures:

  • Water temperature below 40 degrees Fahrenheit – Section 14.9.2 (1).
  • Returning the water temperature to 40°F – Section 14.9.2(2)
  • Critical water levels are 3 inches for pressure tanks and 12 inches for all other tanks, as per Section 14.9.2(3).
  • Water level returns to normal – Section 14.9.2(4).
  • For pressure tanks, critical pressure readings include a pressure 10 psi below normal, as per Section 14.9.2(5).
  • The pressure in the pressure tank is 10 psi higher than normal – Section 14.9.2(6).

6. Rod Run Down to Pipe. Description- A system has pressures greater than 100 psi. According to Section of the 2013 version of NFPA 13, unsupported lengths require an end sprinkler with a hook to prevent upward movement. Question 6. Is it allowed to use an all-threaded rod to prevent upward movement of the pipe?

Answer: According to Annex figure A., tightening the hanger rod to the piping can prevent the end-of-line pendent sprinkler from moving upwards. Hanger manufacturers offer restraining clips to prevent pipes from sliding upward.

This annex figure depicts examples of appropriate hangers for avoiding upward movement.

7. Fire Pump Starting Time and Transfer Times. Description- About two fire safety precautions, this question asks: In the event of a main power outage, the longest permissible wait for a backup power source to take over and the maximum time permitted for a fire pump to activate. Question 7. The longest a fire pump can start is what? What's the longest transfer time to backup power allowed as well?

Answer: There is no known acceptable fire pump startup time. For automatic controllers, NFPA 20, 2022 edition, Section 10.5.2 mandates that the fire pump activates according to pressure drop rather than a predetermined period of time. The fire pump must kick on right away if there is a five-pound pressure drop below the jockey pump start pressure in the system. Once more, there is no time restriction that we are aware of for this automatic pressure activation.

On installations with an automatic transfer switch and an alternate source of power, NFPA 20, 2022 edition, Section 14.2.8 for alternate power supply states that loss of primary source shall be simulated and transfer shall occur when the pump is working at peak load. The handbook commentary explains that the transfer switch and the backup power source should be reached in ten seconds, and the peak flow should be successfully redelivered in twenty to thirty seconds when the primary power source is cut off while flowing at 150 percent of the rated pump capacity.

8. Exterior Stairwell. Description- The outside stairwell is made of steel and concrete, and the wall is rated wood with a noncombustible brick coating on it. About half of the stairwell is open. Question 8. Does Section of the 2019 NFPA 13 intend for sprinklers to be left off of this stairwell? Or do sprinklers have to be installed because the structure is made of combustible materials?

Answer: This section intends for the stair tower to be entirely noncombustible.

According to NFPA 13, 2019 edition, Section, sprinklers can be left off of outside stair towers if the tower is made completely of noncombustible materials and its outer walls are at least 50% open.

In this instance, the linked structure may be of combustible construction, provided the stair tower is 50% open and made entirely of noncombustible materials.

9. UL Listed Antifreeze and Tented Piping. Description- This issue inquires whether the fire code (NFPA 13) permits the use of both special antifreeze and insulation for sprinkler systems in locations prone to freezing. Question 9. Does NFPA 13 permit UL approved antifreeze combined with tent insulation as a solution to freeze concerns?

Answer: Indeed, using antifreeze and tenting together would be a reasonable way to prevent freezing. Nothing expressly stated in NFPA 13 qualifies this as a violation.

10. UL Listed Antifreeze in Existing Systems. Description- The question concerns fire safety systems that use more antifreeze than is safe. It investigates whether division of the system into smaller parts with more risers could be a solution. Question 10. What are the criteria for systems that exceed the maximum volume of UL-listed antifreeze as per the manufacturer's listing? Is it intended to separate the system with more risers?

Answer: Section of the 2023 version of NFPA 25 allows designated antifreeze solutions to be used beyond the parameters for which they were first authorized. The purpose of this clause, as explained in Annex A., is to make it easier to switch from older listed antifreeze solutions like glycerin and propylene glycol to newer ones in systems that might not meet the volume and specific requirements for hydraulic design criteria. This is the case as long as the listing limits for the new antifreeze solution cover the required freeze protection temperature.

The draft modifications for the presently being developed 2026 edition include the system volume restriction within the enforceable regulations. The first draft (see FR-27) says that listed antifreeze solutions can be used outside of their recommended system volume and hydraulic calculation limits as long as the operational temperature ranges are not exceeded. This is as long as the Authority Having Jurisdiction (AHJ) agrees. Here’s the initial draft wording (also attached):

“Where acceptable to the AHJ, listed antifreeze solutions used to replace non-listed antifreeze solutions shall be permitted to be utilized outside their system volume and hydraulic calculation limitations if the temperature ranges are not exceeded.”


To sum up, the purpose of these rules does not always call for the system to be divided into several risers to meet the volume limitations of the listed antifreeze.

Instead, it allows the use of designated antifreeze in systems that are bigger than what is listed, as long as the AHJ agrees (the 2023 version does not need the AHJ’s approval), which protects the integrity of current systems without having to reduce their size. The goal behind documenting this method is to keep current systems functional while switching to safer, specified antifreeze options.

11. Fire Protection System for Mosque Minaret. Description- Putting a sprinkler system in a mosque is a project. The four minarets of the mosque are proving challenging to sprinkler-install. Question 11. Are sprinklers required in these areas?

Answer: NFPA 13, 2022 edition, Section 9.1.1 requires sprinklers to be installed throughout the premises. This provision requires sprinklers to be put throughout the building, unless the standard specifies otherwise. Sprinklers cannot be removed from areas such as minarets or church steeples, according to the law.

Section 9.2 specifies the permitted sprinkler omission locations. The minaret may meet the standards in Section 9.2.1 that allow sprinklers to be omitted from concealed spaces, depending on its construction and access.

12. Baffle Obstruction. Description- In a typical hazard occupation, suspended ceiling baffles are present, as depicted in the figure below for normal spray upright sprinklers. Question 12. Can the three times rule be ignored for non-structural baffles positioned below upright sprinklers, as stated in Section of the 2016 NFPA 13 edition?

Answer: Sprinkler water will reach both sides of the baffles due to their location below the sprinklers. Because baffles are not structural components, they are not subject to the “three-times” requirement outlined in Section The answer would alter if the baffle was close to the ceiling or if the fixture’s top was above the deflector plane. The installation as shown looks to be compliant.

Courtesy: Roland Asp, CET, TechNotes