Abstract: Linear least squares fitting is only applicable to gas detection whose spectral absorption rate is less than 0.1 in coal mine optical fiber gas detection. We present the calculation for gas concentration with damped least squares fitting for the nonlinear issue between the varieties of gas absorption spectrum and concentration if spectral absorption rate increases. Experimental results show that the detection limitation of the method based gas detector is improved from 100 ppm to 30 ppm.Data calibration procedure is also simplified, so the method can better satisfy the requirements of coal mines for secure production.

Key words: damped least square fitting, tunable diode laser absorption spectroscopy (TDLAS), optical fiber gas detection, coal goaf area, spontaneous combustion