The Beelzebub Zone: Rare but predictable failure conditions that can result in accidental fires

This paper proposes the concept of an operational zone, gaps, where normal over-current safeties may not trip unless specifically addressed by design. The analysis concept justarose out of an investigation into a consumer product failure that resulted in a multimillion dollar fire loss. A simple and intuitive means was required to explain and present the failure concept to lawyers, judge, and jury. The presentation, developed as a trial exhibit, further suggested a way to understand the often convoluted or exotic conditions surrounding electrical and electronic failures that result in ignition. The analysis technique applies equally well in the forensic, root-cause analysis of circuits that have or may become implicated in a fire loss, and in the design process. In order to bridge the design community with the forensic and failure analysis communities, this paper reviews the fire investigation process, barriers to investigation, a simple view of fire ignition, and presents a case study where the Beelzebub Zone was used to aid in the loss settlement proceedings. The case study example was taken from a failure of a UL 244A certified device and formed a basis for the concept of the Beelzebub Zone. The case and device identification have been redacted to maintain a suitable level of propriety.