3 ms·

But my lab manager did walk in at one point and immediately recoiled from the fumes (which we were nose-deaf to at that point). I don't know whether it's true

But my lab manager did walk in at one point and immediately recoiled from the fumes (which we were nose-deaf to at that point). I don't know whether it's true or not, but I remember a chemistry lecturer telling me that you don't need to worry about terrible smells in the lab, our noses are sensitive to extremely miniscule levels of chemicals. It's when the levels are so high that they have overpowered our senses and knocked out our sense of smell, that's when you need to worry! A wonderfully paradoxical piece of advice...

somebodynew 4y ago
Hydrogen sulfide is a severe example: it initially smells strongly of rotten eggs but quickly damages the nose until it is undetectable and further exposure can be lethal. For most other chemicals, smells only fade to the background during prolonged lab work through mundane desensitization.
kortex 4y ago
More or less, but with caveats. It's true that many smells (eg H2S, HCN) are detectable before toxic levels, and then become un-smellable at higher levels (saturates and depletes olfactory receptors). But you should still worry about certain terrible smells, because that's often the first sign that something is going wrong. Containment failure, reaction runaway, maybe someone dumped the wrong thing in the wrong waste barrel and now it's reacting, etc. There's also things which are toxic at the same levels as olfaction, and of course there toxins which are dangerous by the time you have smelled them, or you lack the gene to smell. Most really smelly things aren't acutely toxic like that though. Take DMS (dimethyl sulfide, byproduct of Swern oxidation. Smells like boiling cabbage at low concentration, and liquid ass at high concentration. If you are running a Swern in a fume hood, you are likely quite well-contained even if you've made the whole lab smell like a cesspit. When we ran cyanation at the kilo scale, you better believe we had HCN detectors all over the place, wore full-face respirators, etc.
- jamesash 4y ago
  I pass along this amusing advice, no doubt familiar to you, but probably not to the general HN readership. "Gattermann (Ann. 357, 318 (1907)) recommends that the operator smoke during the preparation [of HCN], for he found that a trace of hydrogen cyanide is sufficient to give the tobacco smoke a highly characteristic flavor. This preliminary warning is useful in case of leaky apparatus or a faulty hood" - from Org Syn http://www.orgsyn.org/demo.aspx?prep=CV1P0314 http://www.orgsyn.org/demo.aspx?prep=CV1P0314
toss1 4y ago
Yup, similar to frostbite. Normal skin temp is around 86°F. as it is cooled, it goes from cool to cold sensation, to very painful at around 55°F. Below that, you don't feel anything as it continues to cool to the point where it freezes solid (which wouldn't be a problem if the freeze-thaw cycle didn't create so many little spiny ice structures that break the cell walls; a type of frog has 'anti-freeze' in it's makeup so it can freeze and re-thaw). So, when your skin stops being painful, that's when you really need to warm it up NOW.
- jefftk 4y ago
  > a type of frog has 'anti-freeze' in it's makeup so it can freeze and re-thaw Nit: it can't actually recover from freezing solid. It just has lowered the freezing point of the remaining liquid to below the temperatures it's going to encounter.
  - toss1 4y ago
    Thanks, you provoked me to look it up in more detail, and we're both oversimplifying, and it's even wilder than I thought. From [0]: >> On an organismal level, they are completely frozen to death — their heart stops beating and breathing ceases. Image via Facebook >> The frog’s death-defying trick actually comes down to one simple factor: nucleating proteins. When the frog’s skin begins to freeze, these proteins cause the water within the frog’s blood to freeze first, which in turn serves as a vacuum for most of the water out of the cells. Simultaneously, their bodies pump out large amounts of glucose to serve as stuffing material, which prevents the cells from collapsing. >> Essentially, frogs fill their bodies full of sugar to keep themselves alive through winter. When warm temperatures melt the snow around their hibernacula, frogs slowly thaw back to life. Water melts and returns to the bloodstream, begins circulating, and restarts their heart and breathing. Within an hour or so the frog returns to normal life, completely unscathed. Just wild! [0] https://roaring.earth/frogs-literally-freeze-during-winter-and-thaw-back-to-life-in-spring/ https://roaring.earth/frogs-literally-freeze-during-winter-a...
    - jefftk 4y ago

somebodynew 4y ago

Hydrogen sulfide is a severe example: it initially smells strongly of rotten eggs but quickly damages the nose until it is undetectable and further exposure can be lethal. For most other chemicals, smells only fade to the background during prolonged lab work through mundane desensitization.

kortex 4y ago

More or less, but with caveats. It's true that many smells (eg H2S, HCN) are detectable before toxic levels, and then become un-smellable at higher levels (saturates and depletes olfactory receptors). But you should still worry about certain terrible smells, because that's often the first sign that something is going wrong. Containment failure, reaction runaway, maybe someone dumped the wrong thing in the wrong waste barrel and now it's reacting, etc. There's also things which are toxic at the same levels as olfaction, and of course there toxins which are dangerous by the time you have smelled them, or you lack the gene to smell. Most really smelly things aren't acutely toxic like that though. Take DMS (dimethyl sulfide, byproduct of Swern oxidation. Smells like boiling cabbage at low concentration, and liquid ass at high concentration. If you are running a Swern in a fume hood, you are likely quite well-contained even if you've made the whole lab smell like a cesspit. When we ran cyanation at the kilo scale, you better believe we had HCN detectors all over the place, wore full-face respirators, etc.

jamesash 4y ago
I pass along this amusing advice, no doubt familiar to you, but probably not to the general HN readership. "Gattermann (Ann. 357, 318 (1907)) recommends that the operator smoke during the preparation [of HCN], for he found that a trace of hydrogen cyanide is sufficient to give the tobacco smoke a highly characteristic flavor. This preliminary warning is useful in case of leaky apparatus or a faulty hood" - from Org Syn http://www.orgsyn.org/demo.aspx?prep=CV1P0314 http://www.orgsyn.org/demo.aspx?prep=CV1P0314

toss1 4y ago

Yup, similar to frostbite. Normal skin temp is around 86°F. as it is cooled, it goes from cool to cold sensation, to very painful at around 55°F. Below that, you don't feel anything as it continues to cool to the point where it freezes solid (which wouldn't be a problem if the freeze-thaw cycle didn't create so many little spiny ice structures that break the cell walls; a type of frog has 'anti-freeze' in it's makeup so it can freeze and re-thaw). So, when your skin stops being painful, that's when you really need to warm it up NOW.

jefftk 4y ago
> a type of frog has 'anti-freeze' in it's makeup so it can freeze and re-thaw Nit: it can't actually recover from freezing solid. It just has lowered the freezing point of the remaining liquid to below the temperatures it's going to encounter.
- toss1 4y ago
  Thanks, you provoked me to look it up in more detail, and we're both oversimplifying, and it's even wilder than I thought. From [0]: >> On an organismal level, they are completely frozen to death — their heart stops beating and breathing ceases. Image via Facebook >> The frog’s death-defying trick actually comes down to one simple factor: nucleating proteins. When the frog’s skin begins to freeze, these proteins cause the water within the frog’s blood to freeze first, which in turn serves as a vacuum for most of the water out of the cells. Simultaneously, their bodies pump out large amounts of glucose to serve as stuffing material, which prevents the cells from collapsing. >> Essentially, frogs fill their bodies full of sugar to keep themselves alive through winter. When warm temperatures melt the snow around their hibernacula, frogs slowly thaw back to life. Water melts and returns to the bloodstream, begins circulating, and restarts their heart and breathing. Within an hour or so the frog returns to normal life, completely unscathed. Just wild! [0] https://roaring.earth/frogs-literally-freeze-during-winter-and-thaw-back-to-life-in-spring/ https://roaring.earth/frogs-literally-freeze-during-winter-a...
  - jefftk 4y ago