Given below is a short reminder
list of basic safety principles and specific warnings about hazards
that can occur in a physical chemistry laboratory. Items 1 and 2 are
crucially important. Knowing how to respond effectively in the unlikely
event of a serious accident is essential. Safety information should
be displayed prominently in the laboratory—find it and read it before
beginning any experimental work. Following the list is a
discussion of many safety issues that are pertinent to physical chemistry.
A detailed treatment of all aspects of safety is given in Prudent
Practices for Handling Hazardous Chemicals in Laboratories, prepared
by the National Research Council Committee on Hazardous Substances
and published by the National Academy Press in 1981. 1. Review experimental procedures and identify possible safety hazards before
beginning laboratory work. 2. Learn the location and proper use of all safety equipment available in
the laboratory as well as the fastest method of obtaining emergency
medical assistance. 3. Never work alone in the laboratory. 4. Beware of high-voltage electricity. 5. Never pipette chemicals by mouth; use a pipetting bulb. 6. Wear safety glasses or goggles in the laboratory at all times. 7. Limit the use of open flames and never use them in the presence of flammable
materials. 8. Avoid looking directly into any laser beam. A laser beam or even a reflected
part of such a beam that enters the eye can cause permanent eye damage. 9. Beware of possible explosions due to gas overpressures, especially in glass
systems. 10.
Do not eat, drink, or smoke in the laboratory. Electrical hazards: Several experiments make use of 110-V ac electrical
power and employ apparatus in which exposed metal parts are "live."
If the laboratory table has a metal surface, cover it with an insulating
sheet of plywood or other material before assembling an electrical
circuit. Remember that metal fixtures of all kinds and pipes or tubes
of any kind that carry water are usually grounded. Turn off all electrical
apparatus before altering circuits, if possible; if apparatus must
be left on, use properly insulated test prods and leads. Be on the
lockout for charged condensers, which may not be discharged owing
to a broken circuit or a defective bleeder resistor. Naturally, 220V
represents a greater hazard than 110 V. It should be kept in mind
that the laboratory is often served with 220V in a three-wire system,
with 110 V each side of ground. If 110-V outlets are supplied with
a ground wire and one side of the 220-V line, as much as a 220-V difference
can be obtained in accidental contact between circuits plugged into
outlets serviced by opposite sides of the 220-V line. Shock, if it
does occur, can be a serious matter; medical help should be summoned
at once. Keep the victim quiet and comfortable administer no stimulants
of any kind. Chemical hazards: These are many and varied. It should be taken for granted that any chemical
substance taken by mouth or inhaled is toxic until and unless definite
assurance has been given to the contrary. Reactions that evolve toxic
fumes or vapors or entail risk of fire should always take place in
a fume hood. As a matter of standard safety practice, never pipette
any liquid or solution by mouth; use a rubber pipetting bulb. Mercury
vapor can attain a hazardous concentration in the laboratory atmosphere.
Mercury should be kept in covered vessels at all times. Spills should
be carefully cleaned up (a capillary tube attached to a suction flask
is convenient for this), and inaccessible droplets in floor cracks
and hard-to-reach places should be covered with a light dusting of
powdered sulfur. Another insidious hazard is that of vapors from organic
solvents. Such solvents should not be used indiscriminately for cleaning
purposes, and spills should be avoided. Good ventilation is important. Environmental exposure to
chemical hazards is currently a subject of concern and awareness.
Zero exposure or zero risk of exposure is impossible in practice either
in the chemical laboratory or elsewhere. Part of the professions role
of chemists is to acquire knowledge and to develop judgement as to
which precautions are necessary to limit these risks. One should not
be blindly afraid of every chemical in the laboratory, nor should
one be foolishly fearless. Man chemical hazards can be avoided by
simply not eating or drinking in the laboratory, or breathing large
volumes of vapors. Most chemical poisons are eliminated from the body,
so that the effects of exposure gradually diminish. However, some
poisons are not eliminated completely, and they accumulate, usually
in particular tissues. Recently,
chronic exposure to low levels of certain chemicals has bee shown
to increase significantly the incidence of cancer. Such chemicals
are referred to as carcinogens. The following list gives those chemicals
classified as strong carcinogens by SHA (Occupational Safety and Health
Administration):
None of these chemicals
is used in the experiments described in this book. There are other
chemicals thought to be weak carcinogens on the basis of statistical
inferences involving data from long-term studies on large numbers
of subjects. In these cases, there may be a hazard in industrial settings
from chronic exposure to vapors or direct contact with the skin, but
the risk from brief use in a research or educational setting is not
serious. Chemical bums: Strong acids (particularly oxidizing acids such as chromic acid cleaning
solution) and bases may cause severe bums to the skin. If skin contact
is made, wash copiously with water. If the exposure is to a strong
acid, washing with a very dilute weak base (ammonia) is helpful; for
a strong base use a very dilute weak acid (acetic acid). Particular
attention should be directed to eye protection; safety glasses,
safety goggles, or a face shield must be worn in the laboratory at
all times. Prompt and effective action is essential if any chemical
agent gets into the eyes; a strong base such as sodium hydroxide can
permanently destroy the cornea in a few seconds. Speed is all-important
in getting the exposed individual to an eyewash fountain or other
source of copiously flowing (but low-pressure) water and thoroughly
bathing the eyeball. The eyelids should be lifted away from the eyeball
to facilitate effective washing. Use nothing but water. Get medical
help promptly. Fire and explosion: Any flammable substance provides a potential
fire hazard. In experiments that make use of hydrogen gas or other
flammable gases, not only open flames but also cigarettes and sparking
electrical contacts provide the possibility of explosion. If used
in large quantities, such gases must be vented into the open air outside
the building. A direct exhaust line from the experiment to a nearby
window is best, but an exhaust fan and cross-ventilation will serve.
The distillation of flammable liquids must be carried out in the absence
of open flames; use a steam bath or electrical heating mantle. If
an experiment involves an irreducible risk of fire or explosion, arrange
for an adequate barrier. Safety goggles are required in all
circumstances in which fire or explosion is a possible eventuality.
Know the location of the nearest water supply and fire extinguishers
(use water only on paper or cloth fires). In the event of serious
burns, do not apply ointments or medications; get medical help. Radiation hazards: Ultraviolet light from a mercury lamp or carbon arc is highly damaging
to the eyes. Ordinary glasses give some protection, but the experimental
arrangement should be well shielded so as to decrease the possibility
of accidental exposure to a minimum. Prolonged exposure of the skin
to such radiation can produce severe "sunburn." An optical
laser beam, even from a laser of very low power, which enters directly
into the eye or is accidentally reflected into the eye by a surface,
can cause irreparable damage to the retina as a result of focusing
by the lens of the eye. Eyeglasses provide no protection from this
hazard, and the appropriate laser safety goggles should be worn when
working with such sources (see Exp. 37). Exposure to strong radiofrequency
or microwave fields can "cook" tissue and produce deep internal
burns. Exposure to x-rays and to the radiation from radioactive materials
must be carefully guarded against in experiments dealing with them.
Any such experiments should be done under the direct supervision of
an experienced research worker who will assume personal responsibility
for all required safety measures, and under an appropriate license
if radioactive materials are involved. Mechanical and other
hazards: Most mechanical hazards
are too clearly apparent to warrant mention here. The danger lies
in forgetfulness or casual disregard of risks. Vacuum systems often
carry a hazard of collapse or implosion; bulbs more than 1 liter in
volume should be surrounded by a metal screen or else wrapped with
strong tape to reduce hazard from flying glass particles in the event
of implosion. The bursting of a container due to overpressure is a
frequent cause of accident or injury. A compressed-air line (usual
pressure of the order of 50 psi) should never be connected to a closed
system containing rubber tubing or glass bulbs. No closed system,
except a properly designed combustion bomb, should be attached to
a cylinder of compressed gas (usual maximum pressure: about 3000 psi)
unless a suitable reducing valve is attached; even then, a relief
valve should be provided to guard against accidental overpressure.
Gas cylinders must be chained or strapped to prevent their falling
over. The protective cap must be in place whenever a gas cylinder
is being moved; cylinders should be moved with an appropriate hand
truck, not dragged across the floor. Mechanical pumps must have
belt guards. Unattended operations must
be planned with automatic safety switches that prevent serious damage
(fire, flooding, explosion) in case of accidental equipment failure
or interruption of utility services such as electricity, water, or
gas supplies. Of special concern are the constant flow of cooling
water and the operation of high-temperature baths. In the case of
water flow, a device should be installed in the water line to (1)
automatically regulate the water pressure (so as to avoid surges that
might disconnect or rupture a water hose), and (2) automatically turn
off electrical connections and water-supply valves in case of a total
loss of water supply. In the case of hot thermostat baths or ovens,
a sensor/control device should be installed that automatically turns
off the electrical power to all heaters if the temperature exceeds
some preset upper limit. Safety equipment: Safety glasses or goggles have been mentioned in this appendix
and in other places in this book in connection with specific hazards.
However, use of safety glasses equipped with side shields, or other
approved means of eye protection (plastic goggles alone or over ordinary
prescription glasses, plastic face shields) is usually mandatory
at all times in instructional laboratories, just as it is in industrial
research laboratories. The use of safety goggles is strongly recommended
as standard laboratory policy. Their use is essential in all circumstances
where there exists the possibility of fire, explosion, and implosion,
spattering of caustic chemicals, or flying fragments from machine-shop
operations. Fortunately, very few of these risks exist in the experiments
described in this book, and explicit warnings are given in each case
where hazards do occur. The laboratory should be
equipped with a conveniently accessible safety shower and an eyewash
fountain; there should be more than one of each in a large laboratory.
Increasingly, the fixed type of eyewash fountain is being superseded
by a spray nozzle at the end of an extensible hose; there should be
one of these on each laboratory bench. In lieu of such devices—or
in addition to them—2- or 3-ft lengths of rubber hose (nor small-bore
pressure tubing) attached with wire or clamps to water faucets are
certainly better than nothing. The laboratory should have
convenient access to one or more fume hoods (with a face velocity
of at least 100 ft/min) for any operations involving more than insignificant
quantities of volatile chemicals in open containers. An approved fire extinguisher
[the "dry chemical" (bicarbonate) type is preferred, but
the CO; type is satisfactory] should be mounted near at least one
exit and refilled after every use, no matter how small. The laboratory
should be arranged so as to provide two or more avenues of escape
from any experimental setup in case of emergency. A first-aid kit
containing Band-Aids, sterile gauze, adhesive tape, petroleum jelly,
a mild antiseptic, sterile cotton swabs, tweezers, a set of sewing
needles, a packet of razor blades, and a quick-reference first-aid
manual will provide adequately for most minor emergencies. The location of an inhalator,
a stretcher, and other rescue equipment, if not in the laboratory
itself, should be known. The telephone number of the nearest medical
emergency room and the local ambulance service should be posted conspicuously.
Instructions for emergency evacuation, including special procedures
for evacuating physically handicapped persons, should also be posted.
An evacuation drill held near the beginning of each academic term
is recommended. Under no circumstances
should a person be allowed to work in the laboratory alone. Finally, safety depends
on habits that must be gained outside the laboratory as well as inside.
Thus, on your way to and from the laboratory, look both ways before
crossing the street; after finishing the writing of that laboratory
report, don't smoke in bed (or anywhere else!).
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