Inertial igniters for initiating a thermal battery and methods of preventing initiation of an inertial igniter are provided. A controller controls operation and stop of the fuel cell based on CO concentration and the state of charge of the battery, and stops operation of the fuel cell at a lower CO concentration the higher the state of charge of the battery. Additionally, a method of forming a downhole seal includes disposing in a wellbore a downhole tool including an inner tubular, a lock ring, a lower ring, an upper ring, an insert ring, and a deformable element. The apparatus is calibrated using a synthetic material to mimic the radiant response of live tissue, correcting for background fluorescence and elastic scattering.