Issue 93: Maintaining Sprinkler Systems As They Age
By William E. Koffel, P.E., FSFPE, President, Koffel Associates, Inc.
At least in the USA, the most widely
recognized criteria for the inspection, testing, and maintenance of
automatic sprinkler systems is NFPA 25, Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems.
While there are some limited test requirements for system components
based upon the age of the system, the inspection, testing, and
maintenance requirements do not vary as a function of the age of the
system. It should also be noted that the fire loss experience data that
has been provided to the NFPA Technical Committee on Inspection,
Testing, and Maintenance of Water-Based Systems ("Committee”) does not
indicate the age of the system. As such, it is difficult to ascertain
if the overall performance of an automatic sprinkler system is dependent
upon the age of the system.
Requirements based upon the age of the system
The most commonly cited requirement that is a function of the age of
the system is the need to test a random sample of sprinklers. The
purpose of this test is to determine if the sprinkler is still
operational. Historically, the requirement to test one percent of the
sprinklers from a system applied to sprinklers that have been in service
for 50 years. Once the sprinklers have been in service for 50 years,
additional testing of one percent of the sprinklers is required every 10
years. For sprinklers that have been in service for 75 years, the test
frequency increases to every 5 years.
The procedure used for the test is referred to as a plunge test. The
sprinkler is placed into the test apparatus, exposing the sprinkler to
an airflow that has a controlled velocity and temperature. The
temperature in the plenum of the test apparatus is considerably higher
than the operating temperature of the sprinkler. An air pressure of 0.5
psi (0.4 bar) is placed on the inside of the sprinkler cap. The time
for the fusible element or glass bulb to activate is recorded. If the
sprinkler fails to operate in the specified amount of time, the
sprinkler fails the test and all sprinklers represented by the test
sprinkler are to be replaced.
The frequency of the plunge test requirement for sprinklers using a
fast response element is different. The initial test is required when
the sprinkler has been in service for 20 years instead of 50 years.
The 20 year criteria were established for two reasons. First, fast
response elements are relatively new in the marketplace. Without having
the history associated with standard response sprinklers, the Committee
selected a more frequent test to evaluate the performance of the newly
introduced sprinklers. Secondly, in many cases the fast response
element is used for a specific purpose (life safety, suppression,
etc.). Note that the need to ensure that the sprinkler continues to
operate within an acceptable response time may be more critical than
standard response sprinklers which by definition do not have a maximum
response time index ("RTI”). As data is collected regarding the
performance of the sprinklers using fast response elements is collected,
the Committee could consider revising the threshold at when the plunge
test is required to be performed.
There are also special thresholds for the plunge test for sprinklers
that are installed in what might be considered more harsh environments.
Sprinklers included in this category include:
Solder-type sprinklers having a temperature classification of
extra-high or higher and which are exposed to semi-continuous or
continuous maximum allowable ambient temperatures shall be tested every 5
Dry type sprinklers shall be tested every 10 years due to a higher
susceptibility to corrosion and a failure rate of approximately 50%
after 10 years.1
Sprinklers in harsh environments including, but not limited to:
corrosive atmospheres, corrosive water supplies, cold storage areas, and
battery storage rooms shall be tested every five years. For a more
complete listing of what might be considered harsh environments, see
NFPA 25, A.18.104.22.168.2.
As one might expect, an alternative to the periodic testing of older
sprinklers is to replace all of the sprinklers once the functional test
is required for that particular application and sprinkler.
Whereas corrosion is the gradual destruction of a material, typically
metal, the impact is clearly time dependent. NFPA 25 addresses the
issue of corrosion in various ways. With respect to external corrosion,
sprinklers, sprinkler pipe, and other components of a sprinkler system
are required to be inspected at intervals not to exceed an annual
inspection. While NFPA 25 indicates that sprinklers shall be "free of
corrosion”, Annex paragraph A.22.214.171.124 refers to sprinklers that are
severely corroded and lightly corroded. When one has a concern
regarding the amount of corrosion on a sprinkler, the sprinkler should
be tested to verify performance. However, if a sprinkler is severely
corroded it should be replaced. Tests such as the plunge test do not
address all of the concerns one might have regarding a severely corroded
sprinkler. While the sprinkler may still operate, severe corrosion
could impact sprinkler performance even once it operates (i.e.,
distribution pattern). During recent meetings of the Technical
Committee there has been discussion regarding the need for research to
be performed to assist one in determining when a sprinkler, with some
corrosion, needs to be tested or replaced. However, an argument has
also been made that the actual impact of corrosion cannot be assessed by
a visual inspection and therefore, when corrosion is observed a
representative sample should be tested or the sprinklers replaced.
Internal corrosion is addressed in a slightly different manner. An
internal assessment of metallic sprinkler pipe is required every five
years unless a risk assessment has identified a different interval as
being acceptable. One of the items to be evaluated during the internal
assessment is the presence of corrosion. The impact of corrosion on the
inside of a pipe can be highly dependent on the type of sprinkler
system. When a metal is immersed in water, the rate of corrosion is not
a linear function. In this instance, the rate of corrosion will
decrease as a function of time. Routine testing of the sprinkler system
involving water flow and the introduction of new water into the pipe
will also impact, and could increase, the rate of corrosion. The rate
of corrosion in other types of sprinklers systems, in which water is
introduced into the pipe and then removed, will be different than a wet
pipe system if oxygen is present in the piping system when the water is
removed.2 Internal assessments also provide an opportunity
to identify other concerns such as tubercles or slime (potential
indicators of microbiologically influenced corrosion, also referred to
as MIC) and the presence of foreign organic or inorganic material (such
as zebra mussels) which could obstruct pipe or sprinklers.
Lacking much data regarding the reliability of sprinkler systems as a
function of age, the primary requirement in NFPA 25 that is age
dependent is the testing of sprinklers. Test data has shown that the
performance of some sprinklers is definitely impacted as a function of
the time the sprinkler has been in service. Another age related concern
is that of corrosion which is addressed by periodic visual inspections
of sprinkler system components and a periodic internal assessment of the
piping system. With respect to other performance concerns, NFPA 25
relies on periodic inspections, testing, and maintenance to evaluate the
ongoing performance of the components.
Klaus, Matthew J. "Water-Based Fire Protection Systems Handbook, Fourth Edition”, Quincy, MA: National Fire Protection Association, 2013.
Hart, Frederick L., Leonard Anderson, and Jeffrey Murawski, Water Deterioration From Extended Stagnation Conditions In Steel, Copper and CPVC Pipes, February , 1996.
2nd Quarter 2014 – Building Code Seismic Requirements for
Sprinkler Systems and Special Interface Requirements with Ceiling
Systems – Robert E. Bachman, P.E.
Bachman describes the evolution of building code seismic requirements
over the last 20 years, and specifically the additional requirements for
sprinkler systems beyond those found in NFPA-13. He also discusses how
NFPA-13 has evolved to incorporate these requirements. READ MORE
4th Quarter 2010 – Lessons Learned From Unsatisfactory
Sprinkler Performance: An update on trends and a root cause discussion
from the investigating engineer’s perspective – R. Thomas Long, P.E., Neil P. Wu, P.E., Andrew F. Blum
Automatic sprinkler systems are often the first line of defense in an
overall building fire protection strategy; however, sprinkler systems
have their limitations, and often their performance is affected by
factors not linked to the initial design or installation of the
sprinkler system. This article explores updated automatic sprinkler
system failure data to identify current causes of unsatisfactory
sprinkler performance. READ MORE
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