Bombs in Disposal Pipes

[Sundance]

Isn't this because mailchute/disposal pipes are treated as separate z-levels?
Once I blew up a bomb in a disposal pipe, went down said disposal pipe only to get stuck because the pipes were missing from the blast. There was no damage above it.

I once got stuck in a disposal pipe with a braindead guy. No one helped so i blew my self up with a syndicate bomb, the explosion knocked me and the other guy out alive leaving the place in ruins like a normal bomb.

The fact that you got out alive and not in chunks is the most confusing part..