Most chemicals, barring strong acids and the like, aren’t really that toxic during day to day use. Ask any non-safety-conscious chemist and they’ll chat about running columns benchside with DCM as their primary solvent, the sweet smell of HMPA, or washing their hands with benzene. Warning labels and MSDS aside, it’s hard to argue with the fact that these people are still walking and talking, despite their habit of bringing water (or beer) into the lab.
So, why are we wasting so much money on fumehoods then? It’s all in the long term effects. Aside from acute injuries from compounds that explode or burn, the negative effects of most hazardous chemicals take months or years to develop. As an example from the “do not copy” pile, back in the 1920’s a group of women were hired to paint the dials of high end watches with fluorescent, radium infused paint. Unfortunately for them, after a few dials the cheap brushes they were using would lose their edge, slowing everything down to a crawl and making it almost impossible to “colour inside the lines,” as it were. To combat this, management encouraged these “Radium girls” to wet the brush tips with their lips and tongue.
Given how cautious we are these days with tritium and radiolabeled phosphorus , you’d expect that the first woman to lick her brush must have keeled over instantly. But, the radioactive paint wasn’t acutely toxic. Overdoing things probably led to an upset stomach, but otherwise the dial painters went about their work, day in and day out (some were so saturated with radium that their faces glowed in the dark). It took around three years for the first cancers to appear, and seven before the practice was finally stopped.
Similarly, most carcinogens in the lab aren’t going to kill you then and there, but are more likely to take their toll months or years into the future. Being an organic chemist means (hopefully) being aware of this fact, and within reason doing your best to limit your exposure. Being exposed to one whiff of iodomethane is a death sentence (Max Gergel apparently breathed enough of that particular substance to take down a horse and lived into his 80’s –so far), but if I’ve got to go I don’t want it to be an easily preventable cancer that takes me down.
 In a bit of a twist, research into the Radium Girls helped determine the values we use today as allowable exposure levels for radioactivity.