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A. General Considerations

In the laboratory the chemist works with many potentially dangerous
substances. Yet, with constant alertness, awareness of potential hazards,
and a few common-sense precautions, laboratory operations can be carried
out with a high degree of safety.

Most of the responsibility for the personal safety of the laboratory worker
rests on the worker himself. In the event of an accident resulting from his
neglect of appropriate precautions or disregard of laboratory regulations
he is in a poor position to collect damages for his own injuries, and may
even find himself the target of civil or criminal action if his negligence
results in injury to others. Worse, injuries sustained in laboratory
accidents can result in permanent disability, disfigurement, blindness, or
death a fact that far transcends legal considerations.

The basic rule of safety in the laboratory is: be alert stay alert.

The laboratory is no place for the "absent-minded professor" or the
“absent-minded student” for that matter. Beyond this, take the trouble to
understand what you are doing and to know what the hazards are, take the
appropriate precautions, and use the appropriate protective equipment.

We summarize here some of the more important specific laboratory rules and

(1) Never work in the laboratory alone. Before working in the laboratory
outside regular hours make sure that this is permissible and be certain
that someone else will be in the same room to provide assistance in case of

(2) At all times wear approved eye protection: "safety glasses" with
impact-resistant lenses in approved frames, or protective goggles, or a
face shield, or some combination of these - It should be borne in mind that
this is required by Maryland state law. Safety glasses may be obtained
either ground to prescription or non-refracting. Side shields of
transparent plastic may be clipped on for additional protection. Ordinary
prescription glasses provide about the same protection against spatter as
do safety glasses but in the event of an explosion the lenses of ordinary
glasses are much more easily shattered and the glass fragments may be
driven into the eyeball; in such a case they can be worse than no glasses
at all. Contact lenses (especially the corneal type) provide negligible
protection, and indeed their use may seriously aggravate hazards from
spatter since they will impede washing the cornea free of caustic liquids
that creep or diffuse under them. It is inadvisable to wear them even under
safety glasses, which (it must always be remembered) do not by themselves
provide one hundred percent protection from spatter at top, sides, and

(3) Use the fume hood for all operations involving poisonous or offensive
gases or fumes as well as for operations involving highly inflammable or
potentially explosive materials. A combination of a fume hood and a safety
shield (see below) will provide the maximum readily available protection
against minor laboratory explosions.

(4) Guard against injury from explosion, implosion, flash fires, and
spatter of dangerous liquids by interposing a "safety shield" or other
effective barrier between all personnel and any setup presenting such
hazards. Vacuum distillations of more than small (about 100 ml) quantities
should be shielded, as should gas scrubbing trains containing significant
amounts of corrosive solutions and all evacuated equipment of any
significant size such as vacuum desiccators.

(5) Use a metal safety pail with a well-fitting cover to transport any
dangerous liquid, or more than a small quantity (a pint) of any solvent.
Several years ago the writer (someone at MIT) was a witness to a fatal

accident in which a sealed bottle of ethyl chlorocarbonate, C2H5OCOCl, blew
up (from internal CO2 pressure) in the face of a technician who was
carrying it in one hand from the dangerous chemicals vault. A safety pail
would probably have saved her life.

(6) Never heat an organic solvent in an open vessel over an open flame;
keep a respectable distance between open vessels containing organic
solvents and any open flames or sources of sparks. Except under special
circumstances, an open flame should not be used to heat a reaction
apparatus containing inflammable materials.

(7) Never place beakers or unstoppered flasks containing chemicals in a
refrigerator, even if it is of the "explosive proof" type, or in any other
unventilated enclosure. Never store volatile toxic materials in a
refrigerator or other unventilated enclosure even in a "stoppered" vessel.
The first breath a person takes after opening the refrigerator door could
be his/her last.

(8) Do not work with large quantities of reactants (i.e. more than about
100g) unless you have received special instruction regarding large-scale

(9) Always be careful to avoid pointing the mouth of a vessel being heated
toward any person, including yourself.

(10) Except for certain operations for which special instruction should be
obtained beforehand (reduced-pressure distillations, reactions in bombs or
sealed tubes, etc.) never heat reactants of any kind in a fully closed
system; be sure the system is open to the air at some point to prevent
pressure buildup from boiling or gas evolution.

(11) Never add anything TO a concentrated acid, caustic, or strong oxidant;
instead add the acid, caustic, or oxident slowly and cautiously to the
other ingredients, preferably no faster than it is consumed by reaction.

(12) Never add solids (boiling chips, charcoal, etc.) to a hot liquid as
this may result in violent boiling if the liquid happens to be superheated.
Perform such additions (or put in an appropriate ebullator) when the liquid
is still at room temperature.

(13) Never pipette by mouth any toxic or corrosive substance or
(preferably) anything else. Use an automatic pipette or fill a conventional
pipette with a rubber bulb. (Exceptions to this can be made for certain
dilute non-toxic or slightly toxic solutions used in analytical work: HCl
NaOH, NaCl, NaHCO3, Na2S203, etc. If some of any such solution gets into the
mouth it will be sufficient to spit it out and wash the mouth out well with
water.) Assume any unfamiliar substance to be toxic unless you know
definitely to the contrary.

(14) Be sure all chemical containers axe correctly and clearly labeled.
Labels for your -preparations should contain, besides the name or formula
of the contents your name, the date, and a sample number by which it can be
identified in your notebook.

(15) Never pour anything back into a reagent bottle.

(16) Protect your clothing with a laboratory apron or a laboratory coat.

(17) Protect your hands: with rubber or polyethylene gloves when handling
caustic liquids, with canvas or asbestos gloves when handling hot objects.
Remember that some highly toxic substances can penetrate rubber or
polyethylene gloves; do not hesitate to discard gloves (or aprons, or
coats, even shoes) that become dangerously contaminated.

(18) Dangling neckties, unrestrained long hair, and fluffy or floppy
clothing (including over-large or ragged laboratory coat sleeves) can
easily catch fire, dip into chemicals on the laboratory bench, get
ensnarled in apparatus and moving machinery, etc. Remove or restrain your
long necktie; put up long hair or at least restrain it with a rubber band.

(19) Know and observe the approved procedures for disposal of the chemicals
and laboratory refuse associated with your experiment (see Section F). In
particular, never throw chemical wastes into a waste crock, or
water-insoluble solids into the sink; flush down soluble substances with a
great excess of water; never dispose of cyanides or mercury or alkali
metals in the sink or crock; package hazardous chemical wastes in suitable
containers appropriately labeled; these are taken away every Thursday at
the chemical waste disposal site at Mudd Hall. If in doubt about the waste
call the Safety Office to take them away.

(20) Know the location of exits, fire extinguishers, fire blankets, safety
showers, gooseneck faucets for douching eyes, and other safety devices;
familiarize yourself with the purposes of these devices and with-the
procedures for their use.

(21) Before beginning any procedure with which you have not had adequate
previous experience and thorough knowledge of the hazards, find out what
the hazards and appropriate precautions are by reading the literature
and/or conferring with someone having such knowledge and experience.

This list of twenty-one safety rules and precautions has been chosen
somewhat arbitrarily and is by no means complete. However, it represents a
selection that contains the most important precautions. It should be reread
periodically until observance of these precautions has become second
nature. These same precautions and some additional ones will be treated in
specific contexts in the following sections, which should be read in
advance of performing the corresponding laboratory operations and reviewed
from tire to time. Since observance of the precautions here presented can
be of crucial importance, we do not apologize for being occasionally

B. Fire Protection

Fire is the principal cause of serious laboratory accidents. Nearly all
organic solvents axe inflammable., some of them extremely so, as are many
gases such as hydrogen, acetylene, ammonia, and light hydrocarbons. These
gases and solvent vapors can form explosive mixtures with air.

(1) Solvents

The auto-ignition temperature of a liquid is the minimum liquid temperature
necessary to initiate self-sustained combustion independently of the
heating element. The flash point of a liquid is the minimum liquid
temperature at which the liquid vapor pressure is sufficient to form a
flammable mixture with air, so that once initiated the flame will propagate
through the vapor, often without the liquid itself giving rise to continued
combustion. Flammable limits are the composition limits of a gas mixture
within which a flame, once initiated, will propagate itself. The lower
flammable limit for many solvents (CS2, hydrocarbons) in air is as little
as one or two percent by volume.

In the absence of a flame, a spark, or an incandescent electric heating
element the auto-ignition temperature is ordinarily of serious concern only
with a few substances. Carbon disulfide has an auto-ignition temperature of
about 100 °C, and the vapors can be ignited by contact with an ordinary
low-pressure steam line; the auto-ignition temperature for ethyl ether is
180 °C low enough so that use of an electric hot plate may provide a
significant hazard. Such liquids should be heated with a water bath or a
steam bath in a hood so that vapor from the boiling liquid does not

Of more frequent concern is the flash point. If the flash point of a
solvent is below room temperature (25 °C) the solvent is termed a Class I
solvent. Examples of Class I solvents are the commonly used organic
solvents ether, benzene, methanol, ethanol, acetone, petroleum ether, ethyl
acetate. Precautions to be observed in all operations with Class I solvents
include the following:

a. Never handle solvents near an open flame. If large quantities are being
handled, set up "NO FLAME" signs. Deliberately scout the working area for
lighted burners, pilot lights, electric motors, switches and other sparking
electrical contacts, etc., before beginning your operations and
periodically while they are in progress. Operations in which solvents are
escaping from the reaction vessel should always be conducted in a hood.

b. Conduct recrystallizations on a steam bath or a hot plate (see above
with regard to CS2 and ethyl ether), either in a hood or with a condenser
to contain vapors from the boiling liquid. Use an Erlenmeyer flask (never a
beaker) for recrystallization.

c. Before a liquid is heated to boiling add a boiling chip or some other
device to serve as an ebullator. A superheated liquid may suddenly "bump"
or boil violently, and often will overflow the container and create a fire
hazard. The same may happen if a solid is added to a superheated liquid,
therefore never add solids to a hot liquid.

d. Make sure that reflux and distillation apparatus is tightly assembled
and firmly clamped, with all ground joints well seated. Be certain that
somewhere (at the top of the reflux condenser or at the distillate
-receiver) the system is open to the air (except in reduced-pressure
distillations). Use a mantle, oil bath, hot plate, or steam for heating.
The use of a free flame is never desirable; if a microburner must be used
to melt solidified distillate in some part of the system or for some other
purpose make doubly sure the joints are tight; in this case the vent to the
air should be through a rubber tube with its open end several feet away and
below the flame level.

e. Any quantity of solvent amounting to more than one pint must be
transported in a safety pail and stored in the pail either on a side shelf
(not on a shelf over the laboratory bench) or in a designated cabinet.

f. Never work in a solvent storage area; avoid having large quantities of
solvents in a working area.

g. Eliminate the possibility of sparks of all kinds in the working area.
Electric sparks may come from switches, relay contacts, and thermostatic
devices; the latter are found in heaters, hot plates, and refrigerators.
For this reason these devices whenever possible should be sealed so that
solvent vapors cannot get in or sparks or flame get out; refrigerators used
in the laboratory should be of the "explosion-proof" type, with switches
and thermostat contacts sealed or mounted outside the box. Electric sparks
from electric motors can be avoided by employing induction motors for
stirrers and pumps instead of series-wound and other brush-containing
motors. Electric sparks can also arise from the buildup of "static
electricity". Avoid excessive wiping or swirling of flasks or bottles
containing solvents before pouring; when dealing with more than about a
liter of Class I solvents in metallic systems, ground the apparatus and the
container. Sparks can arise also from metal striking metal or concrete,
and, since solvent vapors are denser than air, a fire could be produced
from a metal object falling onto a concrete floor or even shoe nails
scraping on the concrete. This fact is particularly to be remembered if
there is any spillage of solvents.

h. Never place beakers or unstoppered flasks containing solvents in a

i. Do not smoke, or permit others to do so, while working with solvents, or
(preferably) at any other time in the laboratory. Smoking inside public
buildings, including classrooms and laboratories is not permitted in the
State of Maryland.

(2) Other fire hazards

Clothing and hair can catch fire from a forgotten Bunsen burner, or be
ignited by a flash fire. Avoid fluffy or floppy or ragged clothing,
especially of rayon or cotton, and unrestrained hair or necktie. A person
with hair or clothing on fire may suffer very serious or even fatal burns
unless prompt action is taken. Douse him/her with water at the safety
shower and/or roll him in a fire blanket immediately. Know where the
showers and blankets are, so that the victim will not be a cinder by the
time they are found. If too far from either, use any available source of
water or roll the victim on the floor to snuff out flames. A person who is
afire should not run as this fans the flames.

A number of chemical substances and mixtures are spontaneously combustible.
These include white phosphorus, pyrophoric metals (including hydrogenation
catalysts such as Raney nickel or platinum whose surface is saturated with
hydrogen, palladium and methanol, platinum oxide and alcohol vapors or
hydrogen, finely divided alkali metals), metal alkyls such as dry Grignard
or organolithium reagents, low molecular weight phosphines and borones,
arsine, and iron carbonyl. White phosphorus can be transported and stored
for a time under water, but after long periods acidity builds up in the
water due to slow air oxidation. Beware of storing phosphorus under water
of high alkalinity; if the pH of the water is above 9 the poisonous and
spontaneously flammable gas phosphine, PH3, may be evolved.

Alkali metals are spontaneously combustible in the presence of water (owing
to evolution of both hydrogen and heat) and of certain other substances
such as chlorinated hydrocarbons. Alkali metals should be stored under
purified kerosene or mineral oil (Nujol). Metallic sodium may be used to
dry certain solvents (e.g. ether, dioxane) that contain no active hydrogen
or halogen, for which purpose the metal is usually introduced in the form
of wire extruded from a sodium press directly into the solvent bottle.
Scraps of sodium wire in an empty solvent bottle should be immediately
destroyed under a flow of nitrogen by cautious addition of ethanol or
methanol to the bottle, which is contained in a clean, dry pan or pail;

other alkali metal scraps can be disposed of similarly or placed under
mineral oil in a bottle provided for that purpose. CAUTION: Never put
alkali metal into water, CCl4, or other chlorinated hydrocarbons

(3) Extinguishing a fire

If a fire breaks out, retreat to safety and do not approach to extinguish
the fire until you are sure that it is safe to do so; the fire
extinguishers are usually at or just outside the laboratory doors. When
approaching to extinguish the fire (a) be very careful to leave yourself an
avenue of retreat, (b) take into account the possibility of explosion or
rapid spread of the fire, and (c) be alert for any sign of toxic gases,
particularly phosgene which can be present when chlorinated hydrocarbons
axe involved. Unless the fire is very minor and---. burns itself out very
quickly, call the JHU -emergency number ( dial x7777 ). The principal
classes of fires and the appropriate extinguishers for them are listed in
the following table.

Table 1.1 Fires and Extinguishers

Materials burning,
Never use
of fire
or conditions

Wood, paper, cloth
Water, C02, CC14**


Flammable liquids
Dry NaHC03-type*, CC14




The above, whenever Dry NaHC03-type*, Water,


must be taken into




Alkali metals (also Dry NaHC03-type*, Water,

alkaline earths, Al) Dry graphite*,



(for Na or K)

* Dry solids in cylinder pressurized with N2, a C02 cartridge, or a
propellant such as freon.
** May be used on small fires with adequate ventilation, if the only
type available; not recommended.

The preferred all-round extinguisher, and the most effective in the
particularly important Class B type, is the dry NaHCO3-type or "dry
chemical" type. This is also the best all-around extinguisher for home or
automobile. However, many laboratories are equipped with the C02-type,
which is reasonably effective although in a confined area the C02 gas
released adds somewhat to the hazard of suffocation always present to some
degree at a fire. Soda-acid extinguishers are messy, and even hazardous
when electric appliances or outlets are involved, the use of CC14-type
extinguishers carries the hazard of producing the very poisonous gas
phosgene, and the CC14 fumes are themselves toxic. The use of these two
types is to be discouraged in general. In the absence of the recommended
extinguishers, a small class D fire can be smothered by other inert
(non-reducible), dry materials: reagent sodium chloride or
sodium bicarbonate from a previously unopened bottle, or dry sand.

Whenever an extinguisher has been used, the usage must be reported without
delay so that the extinguisher can be refilled. All extinguishers should be
periodically inspected to insure their readiness for use at any time.

C. Explosions

The term "explosion" is used loosely to denote any reaction in which a
pressure buildup is sufficiently rapid and violent to shatter the reaction
container. Detonations are explosions in which the decomposition, once
initiated by mechanical shock or temperature, propagates at hypersonic
velocity through the medium and results in a destructive shock wave.
Ordinary protective equipment such as safety shields, face shields, and
safety glasses provide at best uncertain protection against detonations,
even with small quantities of material, though they may be better than
nothing. Where detonation is a possibility the reaction should be carried
out behind an adequate barricade or in a remote location, and warning signs
should be posted throughout the area.

Also under the heading of explosions are non-detonating reactions that get
out of control in such a way that the rapid pressure buildup results in
bursting of the reaction vessel and spattering of the contents, or where a
flammable gas mixture inside a vessel becomes ignited with similar results.
Such occurrences are much more common than detonations, and fortunately
have less "brisance". Safety shields and face masks and placement of the
apparatus in a hood usually give adequate protection when the quantities
involved are not large. However, some reactions that may be carried out
safely when under good control at ordinary temperatures may result in
detonation when the reaction gets out of control and the temperature rises
above the detonation level.

Compounds having oxidizing elements -oxygen or halogen- attached to
nitrogen or oxygen may be potential detonating explosives; this is
particularly true of nitrogen compounds, since the great stability of the
N2 molecule which is an important detonation product contributes to the
driving force of the reaction. Groups which may contribute to explosiveness
are: azide (-N3), diazo (-N=N-), diazonium (-N2),, nitro (-NO2), nitroso
(-NO),_nitrite (-ONO), nitrate (-ON02), fulminate (-ONC), peroxide (-0-0-),
peracid ( C03H), hydroperoxide (-O-O-H), ozonide (-O3-), N-haloamine
(-NHCl), aline oxide (=NO), hypohalites (OX-), chlorates (ClO -
3 ;), and
perchlorates (ClO -
4 ). Ether and conjugated olefins may form explosive
peroxides on prolonged exposure to air; many explosions have resulted from
distilling ether to dryness. Always test a small portion of such a solution
with moist starch-potassium iodide paper before distillation; the slightest
blue coloration indicates the presence of peroxide. Heavy metal acetylides,
fulminates, and azides are highly explosive, a fact to be remember if
a heavy metal salt is present in a reaction where acetylene is to be used.
The presence of ammonia and iodine in the same reaction mixture can lead
inadvertantly to the formation of nitrogen iodide which is a powerful
explosive so sensitive when dry that the slightest shock -- such as that
resulting from merely picking up the container -- can set it off.

Compounds of the above types vary widely in sensitivity to shock and
temperature; nitrogen iodide, ether peroxides, and heavy metal azides are
extremely sensitive , while ammonium nitrate is a powerful explosive that
can be set off only with another explosive.

Oxidizing agents such as hydrogen peroxide, sodium peroxide, potassium
permanganate, perchloric acid, nitric acid, chromium trioxide, nitrogen
tetroxide, tetranitromethane, acetyl peroxide, acetyl nitrate, and Tollens
reagent, as well as many compounds of types already mentioned, can yield
explosive mixtures with oxidizable substances. Carbon tetrachloride and
nitromethane may explode during a sodium fusion test. Liquid oxygen, liquid
air, or gaseous fluorine in contact with organic substances may lead to
spontaneous explosion. Traps cooled with liquid nitrogen are capable of
condensing liquid air inside them, which will create a hazard if organic
substances are later condensed; a trap on a vacuum system should not be
chilled with liquid nitrogen until the pressure has been reduced below 1

Among reactions that may require careful attention to control, to prevent
possible explosion, are: nitrations, oxidations (especially with per-acids,
per-salts, peroxides), condensations (Friedel-Crafts, Claissen, Cannizzaro,
Reppe), reductions (Wolff-Kishner, metal hydride), and polymerizations
(such substances as butadiene, acrolein, and acrylonitrile can polymerize

spontaneously and explosively in the presence of a catalyst which may be an
unintended impurity; the same is true of liquid HON and liquid acetylene).
Some intrinsically slow reactions can be speeded up explosively by the
presence of a solubilizer (e.g., NaOH + CHCl3 in the presence of methanol).

It is not possible to avoid altogether working with potentially explosive
substances. Explosion hazard may however be reduced below acceptable limits
by following sensible precautions:

(1) Ascertain the degree of hazard, where possible, by reference to the

(2) Try any unknown reaction with small quantities, with all reasonable
precautions, then scale up. (Beware, however, of the essential
unpredictability and non reproducibility of detonations.)

(3) Compounds that may be prone to detonation should be prepared and
handled only in dilute solution; if then they should decompose, even
violently, the energy of decomposition is largely absorbed by the solvent.
Be sure that transfers are quantitative and washings meticulous so that
explosive residues are not left in vessels or on the desk top by

(4) Have adequate means on hand for moderating the reaction (control of
heat, cooling water, rate of addition of reagents or quenches); if working
behind a barrier, controls should be outside. Always arrange the apparatus
with enough space below so that the heating device can be quickly lowered
and a cooling bath substituted without moving the apparatus itself.

(5) Try to avoid adding a reagent faster than it is consumed, especially in
oxidation, free-radical, and heterogeneous reactions. Never add organic or
other oxidizable materials to a strong oxidant; rather, add the oxidant
slowly and with caution to the other substances.

(6) Be especially alert for indications that something is about to go out
of control: a sudden rise in temperature or pressure, the unanticipated
appearance of fumes or discoloration, evolution of gas, unexpected boiling,
reflux high in the condenser. Any of these may be sufficient cause to
quench the reaction if this can be done in time safely (the procedure
having been well thought out ahead of time); otherwise it should be the
signal to beat a hasty retreat to safe cover, warning others as you go. The
same may be said for a situation where a cracked flask, flame around a
joint, or a loose connection or stopcock appears to foretell immediate
serious trouble. From a safe place, with aid present, carefully appraise
the situation and attempt to control the situation at a distance by
disconnecting heat and/or discontinuing the addition of reagents. With
suitable protective equipment and with help present take whatever
additional steps can be carried out safely to mitigate the explosion and
fire hazards.

D. Caustic liquids

Although the term "caustic" is often reserved for strong bases, the term is
applicable to strong acids and oxidants as well. Concentrated acids
(hydrofluoric, hydrochloric, sulfuric, chlorosulfonic, nitric, chromic,
phosphoric, trichloracetic, glacial acetic, phenol) as well as concentrated
bases (sodium, potassium, and ammonium hydroxides) are injurious to the
human skin and especially to eyes, corrosive to laboratory apparatus and
furniture, and destructive of clothing. If taken into the mouth or
digestive tract they produce widespread destruction of the mucous membranes
and other tissues, which may be fatal. Fumes from some of them
(particularly nitric acid and hydrochloric acid) are injurious to the
respiratory tract and lung tissue if inhaled, and may result in fatal
pulmonary edema.

Some of these substances have high heats of hydration; the thoughtless
addition of water to concentrated sulfuric acid or to solid sodium
hydroxide may result in a violent reaction with dangerous spatter. In
reaction mixtures several of them, particularly the oxidizing acids, may be

involved in run-away reactions which may result in eruption or explosion
with considerable spatter and the possibility of harm to eyes and skin.

Chromic acid cleaning solution, which is often used to remove residual
hydrophobic films (oil, grease) from laboratory glassware, should be
treated with respect. It is made up by the mixing with stirring, of sodium
dichromate with concentrated sulfuric acid; caution is required because
considerable heat is evolved. Contact with the skin rapidly produces severe
burns; contact with wood, paper, cloth, and other organic substances can
produce a fire. Use only where necessary (e.g., with volumetric glassware;
for other purposes use a phosphate-base laboratory detergent instead.
Chromic acid cleaning solution should not be used to remove more than very
small amounts of intractable organic residues in flasks, as a violent
reaction may take place. During use, the solution container and glassware
should be standing in a tray large enough to contain the entire amount in
case of spillage or breakage.

Sensible precautions in handling caustic liquids include the following:

(1) Where there is significant spatter hazard, wear a face shield.

(2) Protect your clothes with a rubber apron or a laboratory coat.

(3) Wear rubber gloves when handling containers.

(4) Work in a hood when any fumes (e.g., HCl oxides of nitrogen) may be

(5) Never pipette such substances (or any other toxic or harmful materials)
by mouth.

(6) Use a funnel if pouring into a narrow-mouth vessel.

(7) Never pour water or a reaction mixture into concentrated acid; pour the
acid slowly, or a small amount at a time, into the mixture.

(8) Wipe up small spills and bottle rings immediately, using rubber gloves
and a wet cloth. A large spill constitutes an emergency that requires
notification of the laboratory instructor. Strong acids on the table top or
floor should be diluted with water and washed down the floor drain, if one
is available; otherwise the diluted acid can be neutralized cautiously with
sodium bicarbonate (which is applied in solid form) and mopped up. Strong
bases should be diluted and washed away or neutralized with solid sodium
bisulfate or sodium dihydrogen phosphate. Beware of spatter in either case.
Toxic acids such as chromic acid cleaning solution should not be
neutralized in any significant quantity with bicarbonate as this may
produce an airborne mist of chromic acid. A large spill of cleaning
solution may be soaked up in a heavily applied layer of dry sand, which is
then shoveled into a metal container and carried immediately outside the
building where it can be shoveled, a little at a time, into a pail of
water. The site of the spillage should then be washed thoroughly; a
neutralizer such as bicarbonate can be applied at this stage.

(9) In case of skin contact, wash the affected part immediately in running
water. A dilute (3%) acetic acid solution or vinegar may then be safely
applied in the case of strong alkali, or sodium bicarbonate or laboratory
soap in the case of strong acid, followed by more washing with water.
Obtain medical help if a chemical burn results.

(10) In case of eye contact, immediately bathe the eyes copiously in
running water: subject the eyes to a copious (but not forceful) flow of
water from one of the gooseneck faucets at the laboratory sink; hold the
eyelids thoroughly open to bathe the eyeballs and undersides of eyelids.
Summon medical help immediately. If alkali is involved, follow the washing
with application of a saturated solution of boric acid. Time is of the
essence; a caustic alkali can destroy the cornea in as little as five
minutes. CAUTION: Boric acid is very toxic and should be used for the eyes
only, never taken internally as an antidote for a base or for any other

(11) In case of ingestion of caustics or inhalation of their fumes get
medical aid immediately ' -Before aid arrives, a person who has ingested
acid or alkali should be given a considerable amount of water to drink;
sodium bicarbon or magnesia can then be safely administered in case of acid
ingestion, or dilute (3%) acetic acid or vinegar or lemon juice (NEVER
boric acid) in case of alkali.

E. Toxic

Almost all chemical substances that are dealt with in the laboratory are
toxic to humans when ingested as liquids or solids or inhaled as gases or
dusts. It makes sense to take normal precautions with all substances to
keep them out of mouth, nose, and eyes, and even off the skin. Some poisons
can be absorbed into the body through the skin, others, -- known as
vesicants -- can attack the skin and underlying tissues causing dangerous
chemical "burns" which are very painful and slow to heal.

Certain substances, because of the high degree of toxicity or the
insidiousness of their action, deserve special mention.

(1) Gases: Carbon monoxide (CO) is universally recognized as dangerous
because it is colorless, odorless, and tasteless, and physiological
symptoms come often too late to give warning. Also in this category for
practical purposes are H2S, HCN, NO, PH3, AsH3, SbH3, and COCl2 (phosgene),
since any of these may be present above the permissible concentration limit
before it is detected by odor. This may be a surprise in respect to H2S,
with its familiar "rotton egg" odor, but there is evidence that small
amounts quickly deaden the sense of smell; this gas is toxic in lower
concentrations than is CO and in not much higher concentrations than HCN.
Other particularly hazardous gases are: acrolein, halogens (F2, Cl2, Br2,
I2), hydrogen halides (HF, HCl, HBr, HI), methyl halides (CH3Cl, CH3Br),
NO2, 03 (ozone), CS2, SO2, CH2N2 (diazomethane), and metal carbonyls. Most of
the gases named are extremely dangerous or fatal for exposures of a few
minutes at concentrations of the order of 100 ppm (parts per million). The
maximum allowable concentration" (often abbreviated MAC) is for most of
these gases of the order of 1 ppm, although for phosphine and its analogues
it is only 0.05 ppm. Ammonia is also toxic but less so on a concentration
basis. Also toxic are ethylene oxide, ethyleneimine, and ketene.

(2) Vapors. The vapors of solvents, particularly benzene, chlorinated (and
brominated and iodinated) hydrocarbons, and esters of mineral acids (e.g.,
dimethyl sulfate) are more dangerous than is commonly recognized. Benzene
is a cumulative poison affecting the blood-forming tissues; it has been
claimed even to cause leukemia. Chlorinated hydrocarbons affect the heart,
circulatory system, and the liver. Even saturated hydrocarbon vapors can
have toxic effects. The vapors of nearly all organometallic compounds such
as tetraethyl lead and dimethyl mercury are toxic in very low
concentrations; the vapor of osmium tetroxide is extraordinarily toxic with
MAC as low as 0.002 ppm. The vapors of Br2, I2, and CS2 have already been
discussed under gases. Prolonged inhalation of mercury vapor may result in
damage to kidneys, eyes, and other organs. The saturation vapor pressure of
mercury at room temperature, about 1.8 x 10-3 torr (i.e., about 2.4 x 10-6
atm or about 20 mg per cubic meter), is about 200 times the MAC (0.1 mg/m3
or about 1.2 x 10-8 atm).

(3) Airborne dusts. Beryllium metal and its compounds (MAC: 0.002 ppm),
heavy-metal compounds, naphthylamines, and certain alkaloids present a high
degree of hazard when they can be inhaled as dusts. Beryllium has a complex
toxicology; some effects of chronic exposure may be delayed as much as 15

(4) Vesicants - Liquid bromine, bis- (beta-chloroethyl) sulfide ("mustard
gas"), the nitrogen mustards beta-haloethylamine derivatives), a-halo
ketones and esters, benzyllic and allyllic halides, and phenol attack the
skin on contact, producing chemical burns and in some cases internal
poisoning as well.

(5) Other substances. We now come to substances that are most likely to
exert their toxic effect through ingestion or skin absorption. The list is
long and we can give here only a sampling. Among inorganic compounds