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Chemical Safety, Part I:
Magnitudes of Hazard
by Christian Thorsten
For the article, "A Look at Chemophobia", please click here.
If you ate eleven pounds of table salt at once, you would die.
A pound would kill you. Even a half a pound would most likely kill you. How about a quarter-pound? Sure, it could be fatal if taken all at once; it would probably result in a miserable, protracted process of organ failure.
Would you die if you ate eleven grams of salt? How about spaced out over a few days?
Chemical safety depends on an appreciation of magnitudes. It does no one any good to categorize everything as "highly toxic".
Material safety data sheets (MSDS's) are sometimes in all-capital letters. Not only does this make the documents harder to read, but it also demeans the very important toxicity and hazard differences between various compounds.
The most obvious place to start with chemical safety is to ask the question: "What would be extremely stupid to do with this chemical?" The most obviously stupid thing to do with any laboratory chemical is to taste or ingest it. (Thinking that one did a synthesis correctly, for example, does not make it safe to taste the product. While one could hardly call the discoverer of sucralose "stupid", his method of discovery ranks in the "Don't Try This at Home" category. In other words, as a chemist he knew the risk he was taking and was prepared to accept it.)
It should be common sense that one does not ingest chlorine bleach or allow children to handle it. The same goes for laboratory reagents. For anyone working with chemicals, the guidelines below should already be quite familiar. In case they're not:
1. Do not ingest or allow another person to ingest the chemical(s). Store chemicals where children cannot get into them. The professional lab hasn't this worry, but the woodshed tinkerer or weekend chemist has to be really careful about this. Chemistry is really not all that special in this respect; it's in the same category as making sure one's children don't play beneath that old project car that's propped up on cinderblocks out back. (This should all be common sense, but as a society we've tampered with the system of what population geneticists call "selective pressures".)
2. Wear eye protection at all times when handling or working with chemical(s). Goggles must cover the eyes, not serve as adornment for the forehead.
There was a sign back in the college chemistry lab. It said "Mary didn't like to wear safety goggles. Now she doesn't need them anymore." Mary was shown walking with a cane and wearing sunglasses. I don't know who originated this quote (you're out there somewhere). The sign was very effective.3. Wear vinyl, neoprene, or nitrile rubber gloves to protect the hands (depending on what you're handling). The gloves will give an extra measure of protection against common acids and caustics. If you are working with heat, wear thick canvas or leather gloves.
4. Do not wantonly mix chemicals. Stick to the instructions in your lab manual or to those approved by your instructor. Some compounds are highly reactive, even with water. Others release poisonous gases under certain conditions. Some common things in the ordinary household can kill you if they are mixed together.
A
great place to start if you want to know the hazards of a given
reaction is Bretherick's Handbook of
Reactive Chemical Hazards. The Merck Index also lists
incompatibilities for many reagents, though it doesn't elucidate the
mechanisms. 5. Work in a well-ventilated area. Do not inhale the fumes or vapors evolved from a reaction or a container of reagent. Odorless does not mean harmless. Carbon monoxide from auto exhaust is a good example.
6. Make sure you are within a short distance of an eye wash station when handling chemicals.
7. Do not allow your work area to become cluttered with papers, etc. Keep an A-B-C fire extinguisher nearby, as well as a special "D" type for metal fires (if your line of experimentation includes that). Read the firefighting section of the MSDS sheet for your specific reagent(s) and make sure you know how to deal with accidental fires. Water is actually dangerous to pour on certain types of fire.
8. Read the label(s) carefully on all reagents you work with. The warnings are there for a reason. If you have chemicals with no label (e.g., prepared them in another experiment), you can usually find and read the MSDS on the Internet, or at least look up the hazards in the Merck Index. MSDS sheets are a little overblown with their use of all-capital letters, and in fact they have done more than their share of spreading chemophobia. Nevertheless, they contain much useful information.
9. Never add water into concentrated acids. Add the acid to the water, one drop at a time, to dissipate the resulting heat slowly. Concentrated acids, especially sulfuric, can spatter all over you from the rapid heating that occurs if you don't follow this guideline.
10. The toxicologist's saying is true: "The dose makes the poison". (Dosis facit venenum, a saying of Paracelsus). Even "harmless" chemicals such as water, salt, vinegar, or baking soda are toxic in large enough amounts. When working with a particular reagent, know its comparative level of toxicity. Know how to minimize your exposure where necessary.
Onward to Chemical Safety, Part II
A Look at Chemophobia
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