I don't actually have all that many deaths. I just meant that when they do happen, that is how. I sometimes get careless or impatient and don't want to designate walls 1 segment at a time to make sure they build them in the right order, I always like to test all my levers, to make sure everything hooked up to the right thing (I'm one of those players with 40 odd levers, 30 bridegs, a hundred floodgates, and hatches, doors, etc all linked, I like each lever to control multiple things if reasonable. So I test everything, and I don't always remember to cease all the hauling tasks or whatever, so sometimes the bridge comes down on top of a stone hauler.
I also enjoy building towers and other constructions outside or in the caverns, and parts of the build team may be attacked. When a couple masons are eaten by a troll, shot by goblins, or just dodge an enraged moose into a pond (recent true story), I count them as build-related, because they were masons and not hoping to be attacked, just unlucky.
Honestly, part of the reason I take risks to build outside is to recover from my old compulsion to just wall in the whole surface for anything I wanted to build up there. Now I only wall in 50% or so...
Also, magma breaching can be tough on a tube.