There are a number of ways to boot Windows 8 or later into safe mode.
For machines that are bootable and you can work within the OS....
Hold Shift Key while clicking reboot
MsConfig, choose Safe Mode from the Boot Tab
For machines that are not bootable there is a trick that I posted here
Link Removed
Which has worked for me reliably in previous and recent testing although I haven't actually tried it yet on 9926
A bit confused as your topic is posted under the Windows 10 Tech Preview section but the Title is "How do you load Windows 8 in safe mode?"
In any event the techniques should work.
EDIT: I think you will find a boot into Safe Mode in Windows 10 extremely disappointing as there is practically nothing...