When you encounter the first Thing Boss, hold Up/Left to run diagonally and you should run under it before it can hit you. This will also aim you directly at the junction box. Immediately start fixing it. As soon as it is almost fixed, hold Right to run through the door. Since he will still keep fixing it as long as you do not release the button, with luck it will be fixed before the Boss attacks for the third time. At the intermission sequence you tend to take off in a random direction, so this may take a few attempts -- save immediately before trying this. If successfully completed, you will lose only about half a bar of health and no ammunition, making the next area much easier.