Of course, all of them are potentially deadly. I say potentially because not a single person died by voidstone door out of 2 playtest groups and third group that I ran through the print version. 18th level PCs have a lot of ways of circumventing doors.
Not all groups are going to go through this adventure the same way, obviously. My group that I ran the print version for had a hard time with The Engineer (area 5), Merkkor (area 13), and of course, Acererak and his Marilith ally (area 20).