by Grant Lobdell

The current NFPA 25 Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems, 2020 Edition, requires testing or replacement of sprinklers exposed to harsh environments on a 5-year basis (

What is a harsh environment?

The term harsh environment is not formally defined (Chapter 3 Definitions) by NFPA 25.  Examples of harsh environments are, however, provided in the Annex of the standard:

A. Examples of these environments are paper mills, packing houses, tanneries, alkali plants, organic fertilizer plants, foundries, forge shops, fumigation areas, pickle and vinegar works, stables, storage battery rooms, electroplating rooms, galvanizing rooms, steam rooms of all descriptions including moist vapor dry kilns, salt storage rooms, locomotive sheds or houses, driveways, areas exposed to outside weather, around bleaching equipment in flour mills, and portions of any area where corrosive vapors prevail.

Upon reviewing the examples given, it appears a harsh environment is typically any environment where the sprinkler may experience accelerated corrosion and/or the excessive accumulation of loading compared to a sprinkler stored in a typical conditioned office, warehouse or living space.  Provided the lack of a clear definition in NFPA 25, the manufacturer of your sprinkler may be the next best resource.  Given their knowledge of their sprinkler’s design, the manufacturer may be able to help you further decide if your particular environment may pose a threat to the life expectancy of their sprinkler.

As is usually the case with fire protection, if you are concerned your environment may be harsh, it is always best to error on the side of caution.  Testing sprinklers from the area of concern on a more frequent basis will provide valuable insight into the environmental impact.  If an environment shows no significant impact on the performance of the sprinkler after several rounds of testing, longer testing intervals shall be permitted (

How harsh environments can impact sprinkler performance?

Much of the concern with the environment examples given in A. are related to those environments leading to accelerated corrosion and/or the excessive accumulation of loading.  Detrimental corrosion can bind soldered mechanism and water seals delaying and/or even preventing sprinkler release in most cases.  Corrosion accumulation on the deflector, particularly between the teeth of the deflector, can change the spray pattern of the sprinkler leading to inadequate coverage of the intended area.

Excessive loading on a sprinkler can lead to the delay in sprinkler response time.  Acting as an insulator, the loading can block the heat from direct access to the release mechanism.  In extreme cases and depending on the type, loading can even prevent the release of sprinkler.  While cleaning of the sprinkler to remove any loading is allowed provided the equipment used to clean the sprinkler do not touch it (A., some forms of loading may be more difficult to remove than others with this technique.

The use of corrosion resistant sprinklers

The 2020 edition of NFPA 25 introduced an exception to the 5-year testing or replacement requirement.  Sprinklers listed as corrosion-resistant are to be tested or replaced on a 10-year basis (  Given the construction of a corrosion resistant sprinkler, typically consisting of a coating or stainless steel design which usually comes at a premium, NFPA 25 has acknowledge that these sprinklers should have a higher life expectancy in corrosive environments and as such have increased the testing window.

If you have any questions regarding this article, please contact Dyne Fire Protection Labs at or (800) 632-2304.

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