Which metal forms the loop used in a Kidde continuous-loop fire detection system?

• A. Inconel
• B. Stainless steel
• C. Aluminum
• D. Brass

Answer: (A)

Continuous-loop fire detectors rely on a sensing loop that stays intact and provides a predictable response as it heats along its length. The loop must withstand high temperatures, resist oxidation, and maintain stable electrical characteristics to provide a reliable trip point in harsh aircraft environments. Inconel fits this requirement best because it’s a nickel-chromium-based superalloy with exceptional high-temperature strength, oxidation resistance, and low creep. That durability keeps the loop reliable in engine compartments and other hot areas, producing a consistent change in the circuit when fire heat is present. Metals like aluminum would soften or melt, brass has a low melting point and creep issues, and stainless steel, while strong, isn’t as stable as Inconel under the extreme conditions, making Inconel the preferred choice for the continuous-loop sensing element.