Choosing the Sample for NFPA 25 Fire Sprinkler Testing

Choosing the Sample for NFPA 25 Fire Sprinkler Testing

By Vincent Powers

Most people in the fire protection industry know that sprinklers are very dependable and effective and can last the life of the building that they are installed in, however verification of their performance is needed, which is why NFPA 25 fire sprinkler testing is crucial.  Sprinklers sit dormant in buildings for years without operation unless there is a fire or accidental discharge.  For this reason, among others, sprinklers are required to be tested in accordance with NFPA 25 The Standard for Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems.

A sprinkler plunge test is what is used to determine the release time of the sprinkler.  In the plunge oven an airstream moves at a constant velocity and temperature. The sprinkler is plunged into the airstream and the time, in seconds, required to raise the temperature of the element is measured. This measurement is called the tau factor.  Multiplying the tau factor by the square root of the air velocity provides a number which is called the Response Time Index or RTI.   This process is necessary to determine the thermal sensitivity of the sprinkler.

The acceptable response times, measured in seconds, based upon the calculated Response Time Index as follows:

Note that corrosion resistant coatings applied by the sprinkler manufacturer are not intended to meet the above criteria.  The acceptable response time of corrosion resistant sprinklers is 180 seconds or the maximum response time for a given temperature rating, whichever is greater.

The requirements for testing of sprinklers are found in NFPA 25, section 5.3. The specific requirements testing of sprinklers are found in sub-sections 5.3.1 through

The standard requires testing of a minimum of four sprinklers or one percent of the total sprinklers installed in a sample area (whichever is greater).  The frequency at which sprinklers are required to be tested is based on the type of sprinkler.

NFPA 25, 2023 edition

  • Sprinklers in service for 50 years then retest at 10-year intervals
  • Sprinklers in service for 75 years then retest at 5-year intervals
  • Sprinkler manufactured prior to 1920- Replace (testing not allowed)
  • Fast response sprinklers (not ESFR and CMSA)- test at 25 years then retest at 10-year intervals
  • ESFR and CMSA sprinklers- test at 20 years then retest 10-year intervals
  • Dry sprinklers 20 years then retested at 10-year intervals.
  • Sprinklers in harsh environments test every 5-years
  • Corrosion resistant sprinklers 10 years then retest at 5-year intervals.

Submitting Samples for NFPA 25 Fire Sprinkler Testing

Section of NFPA 25 states that sample sprinklers that are removed for field sample testing are required to be submitted to an approved testing laboratory acceptable to the AHJ. The annex section adds language stating that a visual inspection should first be conducted in accordance with section

This section states that sprinklers are to be visually inspected from the floor level for signs of leakage, corrosion detrimental to sprinkler performance, physical damage, loss of fluid in a glass bulb, loading detrimental to sprinkler performance, and paint. Sprinklers that have passed the visual inspection should then be submitted for testing. The intent is not to send sprinklers that do not pass visual inspection that would need replacement and are more likely to fail the plunge test.

The question often is what constitutes a sample area for NFPA 25 fire sprinkler testing?

There should be subjectivity in the selection of representative sprinkler samples. The sample areas could apply to the entire building, entire system, or specific areas within a building.

Example: The sample area or groups of sprinklers can be determined by the inspector and/or the building owner.  Keep in mind that sprinklers should be chosen from different floors and areas of the building and not because they are easier to access than other sprinklers.

Highlighting the importance of NFPA 25 fire sprinkler testing

In this example we will use a 10-story apartment building with 100 sprinklers per floor.

If the sample area is to be the entire building, the sample area would include 1000 sprinklers.  This would require 10 sprinklers to be used as test sprinklers (1% of the total installed). Let us assume the cost is for labor, replacement sprinklers and testing are $2,000.00. If one sprinkler in the sample area fails, the remaining 990 sprinklers must be replaced. This could be an absorbent cost to the customer.

In the same 10 story building we could break the sample area into two consisting of five floors each with 500 sprinklers in each sample area.  In this scenario we would have to still send out ten sprinklers for testing (5 from each area) at the same cost of $2,00.00.

If in this situation one sprinkler fails only 495 sprinklers would need to be replaced, at a much less cost to the customer.  For the final example we will choose two floors per sample area, consisting of 200 sprinklers per area.  This would require 4 sprinklers per two floors to be sent for testing, which would be a total of 20 sprinklers at $4,000.00. Again, if one fails only that sample area would need replacing, in this case 195 sprinklers.

As we can see there are benefits and drawbacks to selecting sample areas, and this should be discussed with the owner or owner’s representative to determine the risk vs rewards benefits.  Also note that the sample areas are not up to the AHJ to determine.

One more thing to note is that if there are different types of sprinklers in each sample area, such as sidewall, pendant, and upright that are from different manufacturers, they must be sent in as a different sample.  So, if we had pendants and sidewalls, we would have to send in a minimum of four each or 1%.  The annex clarifies that sprinklers produced by the same manufacturer within a similar environment are permitted to be considered part of the same sample.

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