Water escape from a broken fire protection system

A fire sprinkler spontaneously broke off the end of a pipe, leading to extensive flood damage to an apartment building. MEA Forensic was asked to determine how this came to happen.

The Event:

The fire sprinkler was located in the wall of an apartment. Without warning, the side-wall sprinkler spontaneously broke off the end of its pipe. A significant amount of water came out the end of the now-open pipe and flooded the apartment and the apartments below. Our Failure Analysis experts were asked to determine why the sprinkler broke free of the pipe.

Our Analysis:

First, our experts examined the incident site. We recovered the sidewall sprinkler that broke off, as well as the pipe that the sprinkler had been fastened to. Sprinklers are threaded on the end, in order to tighten them into the threaded ends of pipes. While on site, our engineers measured how tightly fastened the other sprinklers in the same apartment were in order to determine if any sprinklers had been over-tightened.

We observed that the sprinkler had an extra component attached to it called a sprinkler extension. Sprinkler extensions are used when the pipe behind the wall or above the ceiling is slightly out of reach of the end of the sprinkler. The sprinkler extension had broken in two — a circumferential crack through its body had left half of it attached to the sprinkler and the other half still in the pipe. In the laboratory, we examined the cracked sprinkler extension in microscopic detail. We determined that the crack started on the inside diameter of the extension and propagated slowly to the outside. When the crack reached a critical size, the extension suddenly broke in two, releasing the rush of water.

But what started this cracking in the first place? We determined that the extension was made of brass: actually an alloy of about 61% copper and 39% zinc. Detailed microscopic examination of the extension revealed that the zinc had been depleted on the inside diameter and that there were also additional cracks forming beside the main crack. These are clear indications that the crack had initiated due to a type of corrosion called “dezincification”, or DZ. When brass containing a high percentage of zinc is exposed to ordinary potable water, it is possible for the zinc to be dissolved and leave the alloy badly weakened, which is what happened to this sprinkler extension. The root cause of the failure was that the brass sprinkler extension had too much zinc in it.

While current codes and standards permit the use of brass in fire protection systems, they do not permit brass alloys with more than 16% zinc. Hence the high amount of zinc that led to the failure was also a code violation.

The Results:

Our laboratory analysis helped our client demonstrate that the sprinkler extension that failed was defective, while our on-site torque audit showed that over-tightening was not an issue. The failed sprinkler extension did not have any markings to identify its manufacturer, but by comparing the failed extension to exemplar extensions, and via a trail of paperwork and invoices from the installer, we were able to assist the client in identifying the manufacturer.

Our experts regularly make use of engineering techniques and advanced metallurgical microscopy to investigate causes of failure in building systems. If you have questions about whether this kind of investigation may be possible in your case, do not hesitate to contact our forensic engineers.

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