TL:DR – I would definitely suggest venting because even if the fumes don’t bother you now, repeated exposure can lead to sensitivity. It is better to limit your overall exposure so that when you do have the occasional exposure to fumes, nothing happens, which is infinitely better than the 30 days of itchy scaly skin HIPS fumes gave me.
When I first got my printer (a Lulzbot Mini), I immediately started making things with it using HIPS – I was touching the pieces while they were warm, sticking my face right down in the printer to watch, and getting many whiffs of fumes. Within a day, my hands became covered in tiny water blisters on the sides of my fingers and in the webbing between my fingers, and my entire jawline turned red and itchy where the fumes would hit me as looked down on the printing pieces. Over time, the blisters pop and then my skin gets scaly and itchy for about a month until it sheds. This is the same reaction I have with exposure to epoxy or polyester resin – I did a major refurb on a fiberglass boat about five years ago. I started out having no reaction at all, but after about six months, I became extremely sensitive – since then, the smallest amount of epoxy or resin on my skin causes my hands to completely break out in the water blisters I described. Apparantely, HIPS fumes do the same thing to me as well. I talked to my doctor about the epoxy/resin reaction back when it started, and he said that repeated exposure to certain irritants can lead to a permanent allergy for some people, that I got unlucky, and there wasn’t anything to do except not touch the stuff – and as an inverse bonus, I get to keep the allergy for life (it’s my only one – I’ve never had any kind of allergies to anything before this).
The reaction I had to HIPS had me so depressed because I really want to print. So I built a hood for the printer – basically a plywood pyramid, which vents into 4" elbow, which connects to a 4" flexible vinyl dryer hose, then through the wall out of a dryer vent. It’s powered with a 12v bilge blower that is supposed to move 200 CFM. I don’t have an enclosure yet, but I had a big piece of foam poster board lying around, so I block up the front and sides of the printer by leaning pieces of that poster board up against it, along with some random things to block up the sides. I switched to ABS.
I haven’t tried printing in HIPS since building the hood – not even sure I want to self-experiment, though I also don’t want the four rolls I have to go to waste. The ABS hasn’t seemed to bother me (except for maybe the black colored filament, but I somewhat feel that may have been psychosomatic) and I’m basically healed up now, but I’m also using the hood religiously, not using HIPS, not sticking my face in the fumes at all, using the makeshift enclosure to guide fumes into the hood, and also using nitrile gloves to handle warm pieces. It’s kind of a hassle, but nothing like the discomfort of the allergic reaction.