I have never done it, but I understand how to do it. Developing by inspection of panchromatic films is possible with a very weak green safelight, and limited exposure to the light. You must be sure that your eyes are fully acclimatized to the dark, and this can take some time, and you must look at the film under the green safelight for only a very brief period of time. You should do this after the film has been in the developer for a while. The reason for the color green for the safelight is that this is the color the eyes have the most sensitivity to. It is all for the eyes, not for the film, as the film is sensitive to all colors. So, if developing in a tray, you would turn on the green safelight just before you pull the film out to look at, and turn it off just as soon as you have done your inspection. Never leave it on. The exposure of the film to the safelight is additive..the more exposure the more potential fog.