Thanks for the report!  You're right, perhaps I was wrong to make it sound like limonene is completely safe.  Agreed, adequate ventilation is a must. 

Still, comparing OSHA and AIHA standards does seem a bit misleading... are there AIHA standards for those other chemicals? 

There are supplements of coenzyme q10 on the market that contain 100mg of d-limonene, which it claims promotes healthy cell division.  Can't say that about petro solvents!

Swim is very sensitive to chemicals in general, and agrees that he wouldn't wanna be in a room that was saturated with limonene vapors.  However he can't stand to be around petroleum solvents at all... headaches, nausea, etc. come from just a single whiff of that stuff. 

From everything Swim's read, and felt, limonene vapors only cause some irritation and sensitivity, no real permanent damage.  And that paper you referenced mentions mice and liver damage/decreased life span, but doesn't say how they were exposed to the limonene, or how much, or for how long.  That paper is really misleading... I'll bet if they did whatever they did to those mice using naptha or xylene instead of limonene, they'd've been a lot worse off.

While you're right to caution about ass-u-ming that limonene is completely safe, anyone who orders some and tries Swim's acetate-salt-a-huasca tek will see the difference right away.  Swim's never going back to petroleum solvents... huffing dinosaur farts is a thing of the past, for him!  Plus the plant spirits seem to appreciate it more, for whatever that's worth.  8)