It is not uncommon for metallurgical engineers to be asked to participate in fire investigations; not necessarily at the fire scene, but after evidence is collected from the scene to assist fire investigators in determining the cause of the fire. Metallurgical engineers contribute to fire cases and investigations by specifically looking at metal components like arc beads, melted contacts, spalling, chipping, melting, corrosion, and other properties of metal involved in a fire.
Recently, metallurgical engineers from J.E.I. became involved in the investigation of an apartment complex sauna fire. The saunas’ melted heating element was evaluated by metallurgical experts hoping to help find a root cause. An overall view of the sauna heater and heating elements is shown in Photograph A.
Photograph A – Overall view of heating element in failed sauna heater.
The heating elements consist of a metal calrod tubes, which heat up to warm the oven thereby creating dry heat in the sauna. A nickel chrome (Nichrome) helical filament is centralized in the calrod heating element. A close up view of a failed element is shown in Photograph B.
Photograph B – Close up view of failed calrod heating element and helical tungsten filament from sauna heater
The Keyence Digital Microscope was used to examine and photograph melting in another section of the failed calrod. A close-up view, showing a spherical bead of Nichrome, proved that electrical arching had occurred melting the tungsten filament in the subject calrod shown in photograph C.
Photograph C – close up view of Nichrome filament arc melt bead.
As a result of the metallurgical analysis of the fire debris and sauna heater elements, it was determined that an electrical runaway had occurred resulting in arcing and melting of the tungsten filament and calrod heating element.