Rather to my surprise a couple of folk emailed me about this project expressing concern that if I was doing that much soldering I should have some kind of fume extraction.
I do have a simple fan. It does make quite a difference. I got it about a week or so after the bulk soldering properly started. Rather disconcertingly I can still see the smoke rising off the board directly into my face but the fan is having an effect because without it I can smell and feel the fumes and with it I don't.

In a similar vein, a bit of kit I'd not do without now is a set of ear defenders. Each frame requires drilling quite a lot of holes. Hundreds. In both wood and metal. I found the process very tiring. So for the second frame I got a pair of ear defenders and it makes a huge difference. With the noise reduced it's all a lot more relaxed and bearable. Well worth the £20 or whatever it was.

As it happens safety considerations have affected the design. My very earliest thoughts of how the Megaprocessor would look involved being able to sit actually and properly inside it. My first name for the project was the "Walk In Computer". I thought that to be able to sit inside a processor and see stuff happening all around and above you would be fantastic. Thoughts on how to do the "above" bit and what might happen if it went wrong did start to push me in the direction I've gone. The Megaprocessor in total weighs about half a tonne so as a box you'd have to support a 100 kilos or more as its top. Not sure I'd trust me to do that.
Also had to think for a bit about the frames I've ended up with. 2m tall and weighing 60Kg each; you'd notice if that toppled on you.

For the record I've burnt myself with the soldering iron about 5 or 6 times so far. Burnt the carpet 3 or 4 times. And drilled holes in the carpet twice. And pinched my fingers in pliers/wire cutter/aluminium bars half a dozen times. Not yet drawn blood.
The worst injury so far is a burn about half an inch across. Not from soldering but from my watch. I was debugging a board and rested my wrist on it. My watch has a metal strap and it shorted the power supply and started cooking me. It took some seconds for me to notice and then react. And to begin with I assumed it was an insect bite or something so instead of taking off the watch I flapped around looking for the non-existent wasp, wrist burning more and more all the time.