In a sprinkler system incident, the question “What is the cause?” is almost always accompanied by another, more critical one: “Why did this cause occur?” To answer this question thoroughly, a siloed approach is not always sufficient. This is precisely where collaboration between the mechanical engineering department and the materials, metallurgy, and chemistry department becomes an essential investigative tool.

A recent case study illustrates this partnership well: in a refrigerated area, a sprinkler ruptured and triggered a water discharge, affecting several shipments of goods, without any fire or signs of combustion being observed.

A sprinkler typically has a heat-sensitive mechanism (such as a glass bulb or a metal fusible element) designed to activate at a specific temperature. The rupture of this mechanism inevitably results in the release of a fluid, most often water. In this case study, the incident recurred twice in the following months, suggesting a more significant and possibly systemic problem.

Two disciplines, two complementary perspectives

Mechanics focuses primarily on the system: operating conditions, pressures, temperatures, configuration, stresses, and compliance with codes, standards, and the manufacturer’s specifications. In this case study, the mechanical analysis documented key parameters:

• The area was refrigerated (with lower temperatures at the sprinklers than on the floor), an environment conducive to certain degradation mechanisms;
• The system was overpressurized, exceeding both the limit specified by the manufacturer and the requirements of the applicable standard. This excessive pressure alone could hardly explain the sprinkler rupture, but it certainly may have contributed to it;
• The components showed no specific deformation, and there were no particular indications of a snag or activation by a heat source (confirmed, among other things, by infrared thermography);
• The nozzle showed signs of corrosion, and several neighboring nozzles exhibited similar corrosion, which quickly ruled out the possibility of an isolated incident;
• The system contained components that were prohibited by the manufacturers.

The Department of Materials, Metallurgy, and Chemistry, for its part, is “examining” the broken part. What does the fracture reveal? Is there corrosion, discoloration, a metallurgical defect, or traces of an aggressive contaminant invisible to the naked eye? Laboratory examination did indeed reveal various traces, including greenish marks, indicating oxidation of the brass in the presence of moisture and a corrosive environment.

This is where laboratory analyses become crucial.

Scanning electron microscopy (SEM) analysis revealed fracture features associated with brass corrosion, characterized by reddish and blackish areas consistent with dezincification (selective corrosion of zinc). The presence of contaminants was also observed, which may be linked to a potentially corrosive chemical environment. This type of examination confirmed the presence of a slow fluid leak from the fire protection system. In other words: the mechanism and structure of the sprinkler (brass alloy) did not simply “break” spontaneously; they had been chemically weakened over time by a leak that was not immediately detectable.

In fire protection systems, the fluid used is generally water (wet system). In environments exposed to freezing temperatures, the sprinkler system can be kept filled with air (dry system) until activation, or it can contain a mixture of water and glycol to lower the freezing point and prevent the fluid from freezing. In this case, the system uses glycol, and in the event of a slow leak, the mixture of water and glycol can, over time, oxidize in the presence of air and form acidic byproducts (such as organic acids), lowering the pH. This acidification, combined with moisture, can accelerate the corrosion of metal alloys, such as brass—particularly through a process known as dezincification—and thus explains the presence of greenish traces observed on the nozzle, as well as reddish and blackish traces on the fracture surfaces.

Water-glycol mixtures used as coolant typically contain corrosion inhibitors designed to limit metal degradation. However, over time and as the glycol degrades, these inhibitors can become depleted, reducing their effectiveness and increasing the risk of corrosion.

Mechanical buckling: role of overpressure

Mechanics then come into play to contextualize the role of stress: excessive pressure is not necessarily responsible for the break, but it can act as an initiating and aggravating factor by promoting a slow leak of fluid from the fire protection system containing corrosive contaminants and by increasing the stresses on an already weakened component.

A more robust conclusion: the primary cause and contributing factors

This collaboration often leads to a structured conclusion:

• Root cause: degradation of the nozzle’s metal alloy (de-zincing of brass due to a slow leak that created a corrosive environment).
• Contributing/triggering factors: operating conditions (pressure exceeding prescribed limits), selection of certain equipment and components not permitted by the applicable standard.
• Systemic indicators: recurrence of the failure mode, indicating a widespread condition rather than an isolated incident.

Why is this synergy crucial in the context of insurance and litigation?

In a claims case, we are not merely seeking a “possible” explanation, but the most probable and comprehensive explanation:

• Mechanical expertise: analyzes the installation.
• Expertise in materials, metallurgy, and chemistry: analyzes the failure mode.
• Together, they help establish the chain of events leading up to the incident and thus identify the right expert to consult!

This complementary approach is particularly important in sprinkler systems, where certain failures span one field of expertise into another, while remaining interconnected.

Conclusion

Identifying the cause of a fire involving a sprinkler system may require collaboration among several departments. The system is mechanical, but the failure is often material in nature. In the case examined, it was the interaction between the environment, metallurgy, and operating conditions that made it possible to construct a coherent and comprehensive explanation.