Hazards of Working with Chemicals
An Attempt at a Practical Guide
Laboratory chemicals present a real hazard to the lab worker. If you read the Material Safety
Data Sheet (MSDS) on almost any chemical, you will find that it is hazardous. The goal here is
to train you to work with these more or less toxic and corrosive materials without being hurt in
the process. Some materials such as ethanol, sodium chloride, and magnesium sulfate are rather
harmless, while others such as polynuclear aromatic hydrocarbons or radioactive materials can
represent a threat when you are exposed to small amounts. Knowledge of the materials you
work with is your best defense against poisoning or injury. Certainly the MSDS (if one exists)
can give you an idea of the general nature of the materials. Another source is the Merck Index,
Science, Level 4, Marriott Library, RS356 .M524; there is also a copy in 329 JFB. Additional
information can be reasoned out by taking into account the general nature of the material and the
behavior of similar materials. Finally, if in doubt, ask someone who knows.
There are three ways in which chemicals can harm you:
(1) Ingestion (you eat them) : In the laboratory setting this should be extremely rare.
Don’t go around tasting things. Avoid having foodstuff where it could get contaminated
- it’s best not to eat or drink in the laboratory. Extra special care should be taken around
carcinogenic or radioactive materials. While radioactive materials might be relatively
harmless on the outside (for example an alpha emitter), they make for real problems
inside the body, causing cancers. It is reasonable to assume that all chemicals you work
with, with the possible exceptions of ethanol, potassium chloride and sodium chloride,
are harmful by ingestion.
(2) Inhalation (you breathe them into your lungs): Assume that all gases and organic
solvents are hazardous when their vapors are inhaled. Many materials easily pass into the
body through the lungs. Pay special attention to vapors such as hydrogen chloride,
ammonia, hydrogen sulfide, arsine, germanium and phosphorous compounds. Some
solvents such as chlorinated solvents are liver poisons and are readily absorbed. Work
with such materials in a properly functioning fume hood. Make sure you know how to
use the hood. On occasion you may have to work with solvents outside a hood (such as
when cleaning a diffusion pump that is too big to get into a hood) using a chlorinated
hydrocarbon. In such a case, set up a table in front of a hood in a well ventilated room
and work there, so that vapors given off are sucked out of the room. A respirator with a
separate air supply is a good idea for this scenario. Notes: (1) You may not legally use a
respirator unless you have taken the “respirator course” given by EHS; (2) really
important note: real respirators come with screw-on cartridges which are specific for
specific hazards: organics, chlorinated solvents, dust...see Grainger p 2546.
(3) Eye and skin contact : There is no possible return worth the risk of damaging your
eyesight. Working with chemicals without eye protection unequivocally establishes the
fact that you are too stupid to work in this field and need to find another line of work.
Immediately. Hence the Laboratory Policy that anyone working with or
working in a room where others are working with chemicals or glass
vacuum vessels is required to wear safety glasses at all times. Even if you
argue that you are only washing your lunch dishes in the sink, there are still two potential
hazards: glassware falling off the adjacent drying rack and getting flying chips in your
eyes and someone else dumping something nasty into the sink. No amount of laziness is
worth going blind over.
Be aware that some toxic chemicals are readily absorbed through the skin and you could
be poisoned in that way. Some carcinogens can cause skin or other cancers by contact
with the skin. Others are corrosive and will cause severe burns. From a practical
standpoint it is impossible to assure that you will never get any chemical on your skin:
you can’t wear a full body suit all the time and get any work done. You can minimize the
amount of chemicals you get on your skin by wearing gloves and generally being careful
not to spill the chemicals you are handling. But simply wearing gloves is not enough!
You must wear gloves made of a material resistant to the chemicals you
are working with! You should be able to learn what type of gloves are required for
your application by reading the Materials Safety Data Sheet (MSDS) for your material or
looking in a lab safety products catalog. Know the properties of the materials you are
working with, and act accordingly.
Still, you may sometimes get chemicals on your skin. There are various levels of hazard
depending on the chemicals. Some chemicals can cause a chemical burn. (Burn is a generic
term for “tissue destruction”. It is used in the vernacular for hot and cold, acid and base...and
radiation. In all cases you end up with dead tissue. A little dead tissue on your skin is not a
problem...skin cells die and flake off all the time; a lot of dead tissue is a very serious problem.
Think gangrene.)
With respect to strong mineral acids and strong bases, tissue damage is a linear function of
concentration and exposure time and an exponential function of temperature. Generally if you
spill or splash a small quantity of them on most skin you have a few seconds to wash them off
without serious damage. (Everyone gets cuts, scrapes, burns, sunburn, etc. from time to time.
Generally these qualify as “not serious damage” and do not require medical attention.) The
decision to seek medical attention is always a personal one, but it should not be necessary if an
exposure of a few seconds is followed by several minutes of rinsing with COLD water. (The
commonly published number is 15 minutes.) For your amusement, there is a Wikipedia article
on Superacids, acids stronger than 100% sulfuric acid. Curiously lacking from it is the
innocuous-sounding “30% fuming sulfuric acid”; this is pure H2SO4 into which an excess of 30%
SO3 has been injected...it takes up 30% of its weight in water before it gets down to pure sulfuric
acid. The rate at which it removes that water from your tissue leaves you with very serious
thermal burns. This is about as bad as it gets. If you get a tiny drop of 30% fuming sulfuric acid
on your skin, you will be saved by sheer mass: a tiny drop can only do limited damage. If you
get a large quantity on your skin, (a) your “grace period” for starting to wash it off will be
measured in femtoseconds and (b) the only real issue will be where they get the skin for the
graft.
Matt’s Rules of working with acids:
1.
With HCl, when you start seeing little red spots on the back of your hands, it’s time to
wash them off. NOW.
2.
With room temperature nitric acid, when your skin starts to turn yellow, it’s definitely
time to wash it off. NOW.
3.
With sulfuric acid, initially the thermal burns from the extremely exothermic reaction of
the acid sucking the water out of your skin is actually worse than the acid burn. The
thermal burns will generate pain. Pain is Nature’s way of telling you that behavior
modification is in order. WASH IT OFF NOW!
4.
Hydrofluoric acid, the 48% aqueous solution commonly used to dissolve glass, is in a
class by itself. It has two “problems” (1) Skin seems to be relatively permeable to it. It
migrates to your bones where it reacts with the calcium to form calcium fluoride which is
insoluble in water and other body fluids and stays there forever. The bone does not
regrow. (2) Unlike other acids, which cause a burning sensation when they are
destroying your tissue, with HF the pain is delayed. By the time it warns you with pain
that you have a problem, the damage has been done. The tissue is irreparably damaged.
Plastic surgery will be required to replace it. If you work with HF, you must have a
container of calcium gluconate on hand. If you spill HF on yourself, immediately apply
the calcium gluconate prior to leaving for the burn center.
5.
Use common sense when working with acids and bases. The size of the problem is often
a function of quantity. A milliliter of concentrated sulfuric acid represents a risk, but a
small risk. Two liters of concentrated sulfuric should demand considerably greater
attention and precautions. There is a tradeoff with respect to working with gloves:
gloves make you clumsier, so you are more likely to spill and drop and break things. On
the other hand, if you spill, or drop or break something containing acid while wearing
gloves and an apron and a face shield, you are less likely to be hurt. Your decision, you
accept the consequences.
There are two exceptions:
1.
Your “grace period” decreases exponentially as the temperature of the acid increases. At
some point we all learned that chemical reaction rates double for every 10 C increase in
temperature. Do the math. Within a factor of 2-3, your “grace period” is probably 20
seconds with room temperature corrosives. Boiling acid cuts that figure by a factor of
about 28. WHILE YOU ARE MINIMIZING BURN DAMAGE BY RINSING IN
VERY COLD WATER FOR A LONG TIME, YOUR “LAB PARTNER” (ANYONE
WITHIN EARSHOT) SHOULD BE ARRANGING TRANSPORT TO THE BURN
CENTER AT THE UNIVERSITY HOSPITAL. Hot aqua regia definitely fits into this
category.
2.
The boiling point of anhydrous HF (not the 48% aqueous solution, this is the stuff in steel
cylinders) is 19.5 C, so a small quantity of it will boil off your skin (Body temperature is
37 C; skin temperature is 34 or so C.) long before you wash it off. Rushing to the Burn
Center is also pointless because they will inject the burn with calcium gluconate in the
hope of replacing the bone you just destroyed, but it will probably be too late to do any
good. You will be required to make weekly visits to the burn center so they can monitor
the death of the affected tissue. They will wait until all affected tissue is dead before
scheduling surgery, but you must have the surgery before gangrene sets in or you will
have a whole new set of problems.
.
Strong bases, e.g. sodium hydroxide and ammonium hydroxide, have properties similar to strong
acids, but the caustic effects are a little slower; i.e. the “grace period” is a little longer. If you rub
concentrated sodium hydroxide between your fingers, you will discover it to be incredibly
slippery, it will take a long time to wash off and, after you wash it off, your skin will be softer
(and thinner and more prone to cracking). Leaving it on your skin will lead to the same kinds of
burns as acids; the reason it feel slippery is because it is dissolving your skin!.
Oxidizers, e.g. hydrogen peroxide, will oxidize tissue and convert it to a form foreign to your
body and no longer functional, just like strong acids and bases. Concentration is crucial.
Hydrogen peroxide is sold as a 3% solution for medicinal purposes: you use it to cleanse
wounds. The stuff you use in the lab is 30%. It burns tissue at about the same rate as strong
acids or bases: if you begin rinsing it off your skin within a few seconds with cold water you
should suffer no permanent effects. At concentrations of 50% and above, hydrogen peroxide
becomes extremely corrosive to tissue. Use this concentration with extreme care and then only if
you have no other alternative. As we say in Utah, it is the “oxidizer from heck”.
Whether or not medical attention is required will depend on how bad the damage and how large
an area is damaged. Just as it is generally considered unnecessary to seek medical attention for a
first degree thermal or sun burn, you probably don’t need to seek medical attention for a mild
chemical burn that only affects the outer layer of skin. Just as you would definitely seek medical
attention for a third degree thermal burn, you must do the same for an equally severe chemical
burn. In any case, the decision to seek medical attention is yours alone. Be aware that all
University employees are covered by Workers’ Compensation Insurance, so you will not have to
pay for medical repairs unless you fail to submit the paperwork to Workers’ Comp.
Organic solvents are common in the labs. Many are used as solvents for oils. As such, they will
dissolve the oils in your skin. Acetone is a prime example. If you clean an oily object with
acetone on paper without wearing gloves, you will notice that your skin becomes white and dry.
This is because the acetone has dissolved and removed the oil from your skin. Continued
exposure will lead to dryness, redness and chapping, like being out in severe weather for a long
time. Occasional skin exposure is not harmful. Extensive exposure is to be avoided. Such
solvents include acetone, ethanol, methanol, isopropanol, MEK (methyl ethyl ketone), toluene
and xylene. While these materials can be slowly absorbed through the skin, a short time contact
over a small area is not a problem. Wash them off with water. Chlorinated solvents are a greater
hazard. They are more readily absorbed into the fatty layer under the outer skin, and in
continuous exposure over a large area can cause burns and poisoning. Benzene,
trichloroethylene and carbon tetrachloride are comparable to the above in skin sensitivity but all
are carcinogenic. Breathing the vapors (and all are quite volatile at room temperature) for
extended periods of time causes cancers of obscure organs that are difficult to replace; prolonged
breathing of these carcinogenic chemicals is a very bad idea.
By no stretch of the imagination is the above list and guideline intended to be comprehensive. It
is the responsibility of each Lab worker to learn the hazardous properties of each material you
are working with. Two figures of merit are TLV, the Threshold Limit Value and LD50. The
TLV is the maximum concentration permissible in the air you breathe for an 8-hour day and 40hour week. For example, the TLV for acetone, from the MSDS, is 500 ppm and the PEL
(Permissible Exposure Limit) is 1000 ppm. Let’s not quibble about factors of two. 1000 ppm is
0.1%. This is not a small amount! You can smell solvents before you reach dangerous
concentrations. If it smells strongly, avoid breathing it. Assume you are working with a 250 ml
beaker with a diameter of 6.5 cm. At 20 C, such a beaker was determined to lose 33 g of acetone
in 9 hr 20 min. If this acetone evaporates into a room 3 m x 3 m x 5 m in which the air changes
six times per hour (once a design criterion for public buildings), one can calculate the
approximate concentration of acetone in the air to be 5 ppm. Compare this to the TLV of 1000
ppm. On the other hand, the assumption that the concentration of acetone vapor in the room is
uniform, as required by the calculation, is obviously nonsense. If your nose is just above the
surface of a large container of acetone in a poorly ventilated room, you could easily exceed the
TLV. Also remember that the TLV is based on a 40-hour work week; if your exposure is for
only a few minutes a week, the hazard is minimal.
In summary:
Know what you are doing and why.
Know the chemicals you are working with and their properties.
Take precautions (glasses, gloves, shields, etc) as necessary.
Plan for spills:
Design your work to avoid spills
Have spill cleanup equipment ready to use if one does occur
Avoid distractions.
Work safely and carefully.