Evaluation of new regenerated fiber Bragg grating high-temperature sensors in an ISO 834 fire test

Abstract

Temperature, one of the most important parameters in building fires, is now mostly measured with high-temperature thermocouples, which have the typical drawbacks of electric sensors, such as their sensitivity to electrical and magnetic interference. Fiber optic sensors are an alternative to electric sensors and offer many advantages, although their use in fire engineering is somewhat limited at the present time. This paper presents a set of new fiber optic sensors for measuring high temperatures, based on Regenerated Fiber Bragg Gratings (RFBGs). The sensors were placed near the surface of two concrete specimens and then tested under ISO 834 fire curve conditions for one hour. We consider this an important step forward in the application of high-temperature fiber optic sensors in fire engineering, as the sensors were subjected to direct flames and temperature increments of the order of 200°C/min, similar to those in a real fire. The RFBG sensors measured maximum gas temperatures of circa 970°C, in good agreement with those provided by thermocouples in the same position. The gas temperature measurements of the FOSs were also compared with the adiabatic temperatures measured by plate thermometers and concrete specimens surface temperatures calculated with numerical heat transfer models.