Safe Mode is enabled when you open a CrashAutoSave.toe file which is created when TouchDesigner crashes.
This mode opens the file in a static state where nothing will cook. This allows you to edit and navigate the file to investigate cause of the crash, without the file crashing again.
You can rename any file to CrashAutoSave.toe to make it open in safe-mode.
TOuch Environment file, the file type used by TouchDesigner to save your project.