Dyne considers loading to be dirt, dust, or debris. Loading can insulate the thermal element and affect the spray pattern when coating the deflector. Dyne understands that uncovered sprinklers will naturally gather dust. However, it is difficult to tell at what point the loading becomes detrimental to the performance of the sprinkler. As a result, we will report anything that was not on the sprinkler when it was manufactured. It should be noted that loading, especially minimal loading, may not affect the release of the sprinkler as much as corrosion and paint.


Corrosion can physically prevent a water seal from releasing, insulate a thermal element, or alter a water spray. Any visible corrosion, including rust, on the outside of the sprinkler could indicate the presence of corrosion on the inside, which may also be problematic. As a result, Dyne will report any visible corrosion anywhere on the sprinkler. The only exception is corrosion inside the head that would not be visible during a ground inspection as required per NFPA 25 2017 Edition Section 


Paint on the water seal can prevent release and paint underneath a deflector or between the spokes can affect the spray pattern. Similarly, paint on the thermal element may affect the release time. Any paint on the water seal and thermal element will be noted; as well as paint that could be detrimental to the spray pattern. Paint applied to the arms of the sprinkler is not noted because it should not affect the performance. Manufacturer applied paint on these locations will be noted but will be considered “In Spec”. For more information on “Out of Spec”, see Dyne’s February 2017 Constant Contact: When Sprinklers are Out of Specification. NFPA 25 requires replacement of sprinklers that have non-manufacturer applied paint.


Dyne looks for any damage to a sprinkler head. Most often, this would be either a bent deflector, which can affect the spray pattern, or a broken frangible bulb or link, which could affect the release time. Damage to the thermal element, water seal, and arms of the sprinkler could also affect its performance. NFPA 25 requires replacement of physically damaged or leaking sprinklers, including sprinklers that have lost fluid in the frangible bulb.

All four parts of the appearance test are important because they can affect a sprinkler’s performance. However, the results of the appearance test alone will not fail a sprinkler system but rather can help explain why a sprinkler head fails. The most important indicator of the performance of the sprinkler is the plunge test, which tests the sprinkler’s release time. NFPA 25 requires replacement of sprinklers that contain corrosion and/or loading detrimental to sprinkler performance.

For information on NFPA 25 requirements for appearance and response time see LBTR-4402 Sprinkler Head Testing Explanation.

By Evelyn McLaughlin, Chemist

© 2017 Dyne Technologies, LLC

When testing sprinklers, Dyne Fire Protection Labs conducts an appearance test on each one. The appearance test looks for the presence of any loading, corrosion, paint, and/or damage specifically on the release mechanism, water seal, and deflector. Each of these can result in the sprinkler failing to perform properly, either by not releasing in an appropriate time or by changing the spray pattern once released (NFPA 25 2017 Edition Section A. The results of the appearance test are important because they can help identify potential issues with sprinklers. Below is a closer look at each part of the appearance test and what Dyne looks for.