Originally published on Medium — canonical source A kiln shell hot spot that goes undetected long enough costs between one and five million dollars when you count emergency refractory repairs, lost production, and supply chain disruption. I know because I watched it happen — multiple times — across 40 years of cement plant operations. The tragedy is not that the signs were absent. The signs were always there. The tragedy is that we were monitoring for the wrong thing. Most cement plants alarm on absolute temperature thresholds. A shell section hits 380°C and an alarm fires. By that point, the refractory behind it is critically compromised and an emergency shutdown is unavoidable. What we should be alarming on is rate of change. A section rising at 8°C per hour that is currently at 290°C will reach 380°C in roughly 11 hours. That is 11 hours of response time — time to prepare for a controlled shutdown, mobilize refractory crews, and minimize production loss — that threshold-based alarms throw away completely.…