The impacts of thermocouple insulation failure on the accuracy of temperature measurement data in forensic fire-death scenarios-Part I: Physical disintegration.

Thermocouples are utilized to monitor a wide range of temperatures in industrial applications. They are also used in both fire and forensic science research to measure temperatures of fires and of materials exposed to fire. Taking accurate temperature measurements during forensic fire-death scenarios is very difficult due to direct fire exposure to thermocouples, shrinkage and destruction of tissues, and movements from pyre collapse and pugilistic posturing of human donors. This two-part study investigates the impacts on the accuracy of temperature data if the selected thermocouples are unable to withstand fire exposure. Part I (this article) provides an overview of thermocouple theory along with evidence of the physical deterioration that occurs when glass fiber-insulated thermocouple wires are overheated by exposure to fire-level temperatures in a muffle furnace. This study verified that insulation overheating causes embrittlement and disintegration, which can cause the indicated temperature to reflect a new location of measurement located far away from the original measuring junction at the thermocouple tip. Part II will discuss the measurement errors that occurred due to low electrical resistance of insulation when three different thermocouple models were passed through fire-level temperatures to measure an ice bath at a constant temperature of 0°C.

The impacts of thermocouple insulation failure on the accuracy of temperature measurement data in forensic fire-death scenarios-Part II: Low electrical resistance and contamination.

Part II of this two-part article investigates the impact of thermocouple insulation failure on temperature measurement data in forensic fire-death scenarios. Two different models of glass fiber-insulated thermocouple wires (GG-K-24-SLE and HH-K-24 from Omega Engineering) were passed through a ceramic kiln at temperatures up to 1093°C to measure an ice bath at a constant 0°C. In a separate experiment, the same two models of thermocouple wire plus a BLMI-XL-K-18U-120 mineral-insulated metal-sheathed thermocouple probe were passed through a wood pallet fire to measure an ice bath. In the ceramic kiln, the effect on measurement errors was determined for short vs. long exposure lengths and clean insulation vs. insulation contaminated with pork fat. Glass fiber-insulated thermocouple wires showed severe failure in both experiments, with errors ranging from -270°C to almost 2200°C. The metal-sheathed probe showed no evidence of insulation failure and continued to accurately measure the ice bath temperature within expected margins of error around 0°C. This study highlights how exposure of inadequate thermocouples to fire-level temperatures produces severe errors in temperature data. Consequently, it will not be possible to use this data to draw any accurate conclusions about the effects of fire exposure to human donors or animal proxies.