Comparison of Techniques for Prediction of Mechanical Strength of Firefighters’ Protective Clothing Using Near-Infrared Spectral Data

As most textile tests are destructive, non-destructive test (NDT) methods are needed to evaluate in-use firefighters’ protective clothing and to provide guidance as to when to replace this clothing. One NDT method that has shown promise is near-infrared (NIR) spectroscopy. The focus of this research was to examine methods that can be used to analyze spectral data to develop correlations between NIR results and remaining tensile strength of three different Kevlar®/PBI outer shell fabrics after 30–300 s exposures of 10–70 kW/m2 in the cone calorimeter. Four methods of analyzing NIR data were considered: shifts in absorbance at a particular wavelength, changes to absorbance features (area and prominence), and changes to the slope of reflectance curves based on a normalized difference index (NDI) method. While each method had its advantages and disadvantages, the NDI method showed the most promise of the methods considered here, as there were clear trends across the three fabrics over the entire heat flux range. It could also be implemented using measurements at two wavelengths, which would assist in developing a practical device for evaluation of firefighters’ protective clothing in the field.