






                            Downloaded from FireNet Leader
                             (719) 591-7415  Dataline



                                    SOLVENTS

                     by Jack E. Peterson, P.E., CIH, Ph.D.

                                   May, 1987


Acetone
Aromatic Hydrocarbon Solvents
Benzene
n-Butyl acetate
Butyl alcohol
Butyl Cellosolve
Chloroform
Diacetone alcohol
o-Dichlorobenzene
Dichlorodifluoro methane
Ethyl Acetate
Ethyl Alcohol
n-Hexane
Isobutyl Acetate
Isobutyl Alcohol
Isophorone
Isopropyl Alcohol
Lactol Spirits
Methylene Chloride
Methyl Ethyl Ketone
Methyl Isobutyl Ketone
Mineral Spirits
Paint Thinner
Perchloroethylene
n-Propyl Acetate
n-Propyl Alcohol
Toluene
1,1,1-Trichloroethane
Trichloroethylene
Xylene(s)


     All commonly-used solvents share two health hazards, those of narcosis and
of skin irritation caused by defatting.  "Narcosis" means "sleepiness," and the
principal problem associated with overexposure to materials that cause narcosis
("narcotics"--a scientific term having little to do with street drugs) in
industry is that of accidents caused by inattention.

     Skin irritation from the common fat/grease solvents is quite common.  These
materials, in general, are not severe irritants but, instead, cause problems by

                                  SOLVENTS.TXT
                                     Page 1













                            Downloaded from FireNet Leader
                             (719) 591-7415  Dataline


defatting the skin.  Defatted skin cracks easily and is much more prone to
infection than is normal skin.  Casual minor skin contact will usually not cause
much of a problem; rashes are usually associated with chronic (long term,
repeated) contact.


Acetone

     The least toxic oxygenated hydrocarbon solvent in common use is ethanol
(ethyl alcohol); the next-most toxic is acetone.  Acetone vapor is only slightly
irritating to the eyes and respiratory tract; in even higher concentrations it
is slightly narcotic.  The PEL is 1000 ppm.  In 1979 ACGIH declared an intention
to reduce the TLV to 750 ppm to reduce the possibility of respiratory tract
irritation, coughing, and headache and did so 3 years later.  The threshold for
eye irritation may be as high as 6000 ppm for some people.  Minimal central
nervous system depression is experienced at 12,000 ppm.

     Acetone has never been implicated in occupational illness.  Its TLV is
based much more on good practice than on toxic effects.  As with ethanol,
acetone is a normal metabolite in biological oxidation; it therefore, does not
accumulate in the body at all.  It has no effects from prolonged, repeated
exposure that are different from those experienced from short term exposure.

     As with all good solvents, acetone can remove fats from the skin, causing a
rash and making it more susceptible to infection.


Aromatic Hydrocarbon Solvents

     Many of the kerosene-like mixtures called "mineral spirits" and "Stoddard
solvent" contain appreciable fractions of aromatic hydrocarbons in addition to
aliphatic and alicyclic hydrocarbons.  With a boiling range of about 154 C to
202 C the Stoddard solvents are not particularly volatile and should contain no
hexane or benzene.  The main effects of these mixtures on man appear to be
irritation, especially of the eyes and skin, and defatting of the skin.  ACGIH
has recommended (1987) that its TLV of 100 ppm be retained for this material
despite a NIOSH recommendation of about 60 ppm.  OSHA still uses a PEL of 500
ppm based on an older TLV.


Benzene

     Also (but incorrectly) called "benzol," and not to be confused with the
petroleum naphtha called "benzine," benzene today has only limited use as a
solvent for two reasons.  First, it is more valuable as a chemical intermediate
and gasoline octane improver and second it is rather high in toxicity.

     Alone among the hydrocarbons, benzene has the ability to interfere with the

                                  SOLVENTS.TXT
                                     Page 2













                            Downloaded from FireNet Leader
                             (719) 591-7415  Dataline


synthesis of blood components upon chronic overexposure.  This has led to
aplastic anemia and in some cases, leukemia along with other less serious blood
changes.  Exposures required for aplastic anemia and/or leukemia to develop
appear to be years at and above about 200 ppm although in rare cases, aplastic
anemia has developed after chronic exposure at about 60 ppm.

     Acutely, benzene is a pleasant smelling (aromatic) narcotic.  Its ability
to induce narcosis is on the same order as that of toluene and much better than
most of the aliphatic hydrocarbons.  It is, of course, flammable and explosive.
Its explosive range is 1.3 to 7.1% in air and its flash point is 12 F.

     In 1977 OSHA issued an Emergency Temporary Standard of 1.0 ppm for benzene.
This was immediately challenged in the courts and was later voided by the
Supreme Court.  The current (1987) OSHA PEL time-weighted average (TWA) for
benzene is 10 ppm with a 50 ppm ceiling.  The TWA coincides with the TLV but not
the NIOSH Recommended Standard of 1.0 ppm (a "1-hour ceiling").  ACGIH's STEL is
25 ppm and both that and the TWA have been given the A2 ("Industrial Substances
Suspect of Carcinogenic Potential for MAN") designation.


n-Butyl Acetate

     Butyl acetate is similar to the other lower aliphatic esters in its
toxicity and hazards.  It is irritating to both the eyes and the upper
respiratory tract; the TLV (and PEL) of 150 ppm was set at that level to prevent
eye and upper respiratory tract irritation.  No adverse effects from acute or
chronic exposure have been reported.  This material, however, is probably
narcotic in high concentrations.

     n-Butyl acetate is much better known, toxicologically, than isobutyl
acetate.  Effects of both materials are quite similar; their TLVs and PELs are
identical, 150 ppm.


Butyl Alcohol

     Of the three butyl alcohols, n-butyl (n-butanol) is the most commonly
encountered and also the most toxic.  It has a TLV of 50 ppm as a ceiling in
contrast to the 100 ppm for tert-butyl and 100 ppm for sec-butyl alcohols.
Furthermore, n-butanol can be absorbed through the intact skin in acutely toxic
amounts while skin absorption does not appear to be a problem with the other
isomers.

     n-Butanol is capable of enhancing hearing loss in young people exposed to
excessive amounts of noise.  It is also irritating to the eyes and has a
threshold of about 10 ppm for its rather unpleasant characteristic odor.  Its
TLV of 50 ppm as a ceiling was set to avoid increased hearing loss and eye
irritation.  OSHA uses 100 ppm as the PEL from an older TLV.

                                  SOLVENTS.TXT
                                     Page 3













                            Downloaded from FireNet Leader
                             (719) 591-7415  Dataline



     Both sec-butanol and tert-butanol are more narcotic than is n-butanol and
are more volatile.  TLVs for these materials were set to avoid narcosis.


Butyl Cellosolve

     Ethylene glycol n-butyl ether (2-butoxy ethanol, Dowanol EB, butyl
Cellosolve) is a mild narcotic at best, is irritating to the eyes and mucous
membranes, and, upon overexposure (particularly chronic), is capable of causing
destruction of red blood cells (hemolysis), liver and kidney injury.  Injury to
workers is uncommon, however, probably because this solvent has a low volatility
and vapor concentrations as high as the TLV of 25 ppm (or PEL of 50 ppm) are
rare.  Because butyl Cellosolve is rapidly absorbed through the intact skin,
skin contact can be much more hazardous than vapor exposure.


Chloroform

     Trichloromethane or chloroform was the first chemical used to replace ethyl
ether as an anesthetic (to avoid the fire/explosion hazards of the ether).
However, surgeons and others soon noted that patients who had been anesthetized
with chloroform and who did not develop cardiac arrhythmia during the operation
(with attendant cardiac arrest) often recovered to develop kidney or liver
disfunction.  Nevertheless, for many years chloroform was regarded as being much
less toxic than carbon tetrachloride and was often substituted for carbon
tetrachloride in solvent applications for that reason and because it shares with
carbon tetrachloride lack of fire and explosion hazards.

     In the 1950s, however, the suspicion began to grow that chloroform was much
more toxic than had been thought.  Animal inhalation experiments coupled with
epidemiologic surveys of exposed people confirmed that suspicion.  The TLV for
carbon tetrachloride is 5 ppm while the TLV for chloroform is 10 ppm.  Both are
suspected by the TLV Committee of being carcinogenic for man and have been given
the "A2" designation.  The current OSHA Standard for chloroform is 50 ppm; NIOSH
has recommended a Standard of 2 ppm as a 1-hour ceiling concentration for this
material.  Chloroform and carbon tetrachloride are simply too toxic and
hazardous to be used casually as solvents.

     Other than narcosis and cardiac sensitization, the main action of absorbed
chloroform is on the liver and kidneys.  As with other materials, the liver is
the chief "detoxifying" organ for chloroform and the kidneys, of course, are
responsible for excretion of it and metabolic products in the urine.  Because
the liver also detoxifies ethyl alcohol and because alcohol has been shown to
potentiate the toxicity of several other liver toxins, it is also probably
capable of intensifying the toxicity of chloroform.  And, all good fat solvents
are capable of defatting the skin; chloroform is no exception.


                                  SOLVENTS.TXT
                                     Page 4













                            Downloaded from FireNet Leader
                             (719) 591-7415  Dataline



Diacetone Alcohol

     Chemically, diacetone alchols is 2-methyl-2-pentanol-4-one or 4-hydroxy-4-
methyl-2-pentanone, an aliphatic alcohol-ketone.  It has a rather pleasant odor
at its TLV (and PEL) of 50 ppm that becomes unpleasant and irritating at twice
that concentration.  At much higher concentrations it is narcotic.  The TLV was
set to avoid irritation to the eyes and upper respiratory tract and unpleasant
odor.


o-Dichlorobenzene

     Chemically, o-dichlorobenzene is 1,2-dichlorobenzene; it may be called
"DCB" or other "pet" names.  This material has its primary effects on the blood-
forming system and liver and secondarily on the kidneys.  Several case reports
in the literature indicate that leukemia and/or anemia may result in man from
chronic overexposure.  It is capable of causing narcosis and has a typical
solvent action on the skin; it is absorbed slowly.

     The OSHA PEL for o-dichlorobenzene is 50 ppm as a time-weighted average.
ACGIH applies its "ceiling" designation to that number so that 50 ppm should not
be exceeded.  This was done to prevent most eye and nasal irritation as well as
to prevent the more serious toxic effects.  This material is regarded as having
a relatively low toxicity for humans.


Dichlorodifluoro methane

     Dichlorodifluoro methane, also called "refrigerant-12," (to avoid using
DuPont's "Freon-12" designation) is colorless, tasteless, and almost odorless.
It has a TLV (and OSHA PEL) of 1000 ppm, a value set more because it indicates
good practice than because of any hazards even at several multiples of the TLV.
If a large tank containing the material should rupture there might be a hazard;
probably some people nearby would become dizzy and others might pass out.
Recovery from such an episode would probably be full and complete.


Ethyl Acetate

     Ethyl acetate is one of the most-used lacquer and ink solvents and has an
excellent record of very few deleterious effects on people who use it.  At its
TLV (and OSHA PEL) of 400 ppm, its odor (mild, fruity, pleasant) is strong and
unacclimated people may experience some upper respiratory tract irritation in
the first few minutes of exposure.  Ethyl acetate is a mild narcotic; exposure
to very high concentrations may cause some dizziness or sleepiness.  The
literature indicates that some people have become sensitized (respiratory tract)
to this material, but that certainly is not a common problem or even a likely

                                  SOLVENTS.TXT
                                     Page 5













                            Downloaded from FireNet Leader
                             (719) 591-7415  Dataline


one.

     Ethyl acetate can defat the skin, but is not particularly irritating
otherwise.  Its volatility usually prevents prolonged skin exposure.


Ethyl Alcohol

     Ethyl alcohol (ethanol) is, of course, best known as a beverage and as
such, has been consumed by man since pre-history.  Overexposure (by ingestion)
causes the form of intoxication known as inebriation, a manifestation of the
ability of this material to cause generalized depression of the central nervous
system, including narcosis.

     Ethanol is the least toxic of the commonly-encountered solvents and, of
course, of the alcohols (because of its relatively rapid and complete metabolism
to carbon dioxide and water).  In high concentrations (on the order of 5,000 ppm
or greater), however, it can cause irritation of the eyes and upper respiratory
tract.  Even higher concentrations are probably required to cause any narcosis.
Its TLV (and PEL) is 1000 ppm.


Hexane

     n-Hexane was long regarded as a typical member of the series of aliphatic
hydrocarbons with minimal narcosis as its main acute effect and no differing
chronic toxicity.  Then, chronic exposure to n-butyl ketone was found in to
induce peripheral polyneuritis and polyneuropathy through oxidation to the
diacid form.  Studies with animals showed that n-hexane in the body followed the
same biochemical pathway and explained some puzzling results of earlier studies
where hexane was the principal solvent used.  Polyneuropathy has apparently
resulted from chronic exposure to hexane at a few hundred ppm.  Its current PEL
is 500 ppm but the TLV is 50 ppm with no suggested STEL.  Other isomers (having
the general formula of C6H14) have TLVs of 500 ppm and STELs of 1,000 ppm.
     
     Hexane has a flash point of -7.0 F and an explosive range of 1.1 to 7.5% in
air.

     
Isobutyl Acetate

     Isobutyl acetate is similar to the other lower aliphatic esters in its
toxicity and hazards.  It is irritating to both the eyes and the upper
respiratory tract; the TLV (and PEL) of 150 ppm was set at that level to prevent
eye and upper respiratory tract irritation.  No adverse effects from acute or
chronic exposure have been reported.  This material, however, is probably
narcotic in high concentrations.


                                  SOLVENTS.TXT
                                     Page 6













                            Downloaded from FireNet Leader
                             (719) 591-7415  Dataline



Isophorone

     A more generic name for isophorone is trimethyl cyclohexenone; the material
is an alicyclic ketone.  Concentrations on the order of 25 ppm are capable of
causing irritation of the eyes and upper respiratory tract of people not
"hardened" to such exposures.  Prolonged exposure to lower concentrations has
caused feelings of fatigue and general ill health.  To avoid such symptoms the
TLV was set at 5 ppm as a ceiling value that should not be exceeded for more
than a few minutes.  OSHA uses an older value of 25 ppm for its PEL; that
concentration is not sufficiently low to prevent uncomfortable irritation and
other symptoms such as fatigue and malise.


Isopropyl Acetate

     Isopropyl acetate is much more of an irritant to the eyes than it is to the
respiratory tract.  At its TLV (and PEL) of 250 ppm, it will probably irritate
the eyes of the unacclimated.  At that concentration the odor is pleasant.  No
human systemic effects have been reported in the literature although high
concentrations can probably cause narcosis.  Eye irritation, however, should act
to prevent voluntary overexposure to concentrations that could prove injurious.
Its STEL is 310 ppm.


Isopropyl Alcohol

     Isopropanol enjoys widespread household use as "rubbing alcohol."  At its
TLV (PEL) of 400 ppm it is mildly irritating to the eyes and upper respiratory
tract to the uninitiated.  At twice that concentration the irritation is severe
enough to be uncomfortable.  Although isopropanol is a narcotic in high
concentrations, chronic exposure to 400 ppm produces no such effects.  The STEL
is 500 ppm.  Occupational injury from isopropanol has not been reported.

     Isopropyl alcohol can be absorbed through the intact skin in acutely toxic
amounts but the surface area contacted must be large for the effects to be
severe.  It can defat the skin but otherwise is not particularly irritating.


Lactol Spirits

     "Lactol Spirits" is a trade name for a petroleum hydrocarbon fraction that
contains a high percentage of aromatic compounds such as toluene and xylene(s)
(which see).


Methylene Chloride


                                  SOLVENTS.TXT
                                     Page 7













                            Downloaded from FireNet Leader
                             (719) 591-7415  Dataline


     Of all the chlorinated aliphatic hydrocarbons, methylene chloride
(dichloromethane) is one of the two that are least toxic (the other is 1,1,1-
trichloroethane).  This material has little ability to injure the liver and
kidneys; instead, it is converted in the body to, among other things, carbon
monoxide.  Following exposure to methylene chloride, the carboxyhemoglobin level
in blood rises just as if the exposure had been to carbon monoxide, but slower.
As the rise in carboxyhemoglobin is slower, so is the fall and, in consequence,
the "exposure" to higher-than-normal carboxyhemoglobin levels is more prolonged
than if carbon monoxide had been inhaled.  Discovery of the body's ability to
convert methylene chloride to carboxyhemoglobin caused a reassessment of the
various control concentrations for this material.  In addition to that effect,
methylene chloride is a weak narcotic (causing drowsiness); it can, of course,
defat the skin.

     The OSHA PEL for methylene chloride is 500 ppm with a ceiling of 1000 ppm
and a limit of 2000 ppm for 5-min peaks no more frequent than once in 2 hours.
This PEL was derived from the ANSI (American National Standards Institute)
"Acceptable Concentration" for methylene chloride.  The NIOSH Recommended
Standard is 75 ppm for a 10-hr day, 40 hr week, with a ceiling of 500 ppm for
any 15-min exposure.  To compound confusion, the ACGIH 1987 TLV for methylene
chloride is 100 ppm with an "A2" (Suspected of Carcinogenic Potential for MAN)
designation and an intention to reduce the TLV to 50 ppm.

     Methylene chloride has no flash point but can be exploded in
concentrations ranging from 15.5% (155 000 ppm) to 66% (660 000 ppm) in air.


Methyl Ethyl Ketone

     Usually called MEK, methyl ethyl ketone (butanone) is one of the least
toxic of the commonly-used solvents (its lower homolog, acetone, is still less
toxic).  Only a very mild narcotic, MEK is sufficiently irritating to the eyes
and respiratory tract to prevent voluntary overexposure to hazardous
concentrations.  At the 200 ppm TLV (and PEL), there may be some mild eye
irritation; the STEL has been set at 300 ppm.  Gross chronic overexposure
including skin contact to an unknown extent has caused numbness of the fingers
and arms in people also exposed to methyl n-butyl ketone.

     MEK can defat the skin, but is not particularly irritating otherwise.  Its
volatility usually prevents prolonged skin exposure.


Methyl Isobutyl Ketone

     Methyl isobutyl ketone is usually called MiBK or MIBK wherever it is used.
For many uses, it has replaced methyl n-butyl ketone (MBK) as that material has
been found to induce peripheral neuropathy upon chronic overexposure.


                                  SOLVENTS.TXT
                                     Page 8













                            Downloaded from FireNet Leader
                             (719) 591-7415  Dataline


     MIBK (Hexone, 4-methyl-2-pentanone) is moderately irritating to the eyes,
upper respiratory tract, and skin.  At its PEL of 100 ppm it is somewhat
irritating and at 200 ppm, eye irritation is apparent and the odor is
objectionable to many people; at 400 ppm irritation to the eyes and upper
respiratory tract is quite severe.  To avoid such effects the TLV has been
reduced to 50 ppm with a STEL of 75 ppm.  The warning properties (irritation,
odor) of MIBK appear to be adequate to prevent unknowing overexposure.  There
are few, if any, indications that chronic exposure to MIBK has effects different
from those of acute exposure.

     MIBK can defat the skin and, in addition, is sufficiently irritating to
cause dermatitis upon prolonged, repeated contact.


Mineral Spirits

     The phrase "mineral spirits" is essentially meaningless except that it
indicates a derivation from petroleum.  Usually the materials so-designated are
largely aliphatic hydrocarbons such as the hexanes, heptanes, octanes, etc; the
compounds actually present are a function of the boiling range of the mixture.
Petroleum hydrocarbon napthas and solvents are difficult to describe
quantitatively or qualitatively because of the very complex mixtures usually
involved although the term may be applied to materials having a boiling range
below that of Stoddard solvent.  So long as the benzene and hexane
concentrations are low (as they should be), the most severe hazards are probably
narcosis and some irritation, especially of the eyes and skin, and defatting of
the skin.

     Acute and chronic overexposure to petroleum solvents have been linked in
some studies with injury to the central nervous system (CNS).  This kind of
problem appears to be associated only with relatively gross overexposure.

     ACGIH has recommended (1980 and later) that its TLV of 100 ppm be retained
for Stoddard solvent but has promulgated no TLV for mineral spirits because it
considers that term and "White Spirits" to be synonyms of Stoddard solvent.
There is a NIOSH recommendation of about 60 ppm also for Stoddard solvent.  OSHA
still uses a PEL of 500 ppm based on an older TLV.


Paint Thinner

     Many different materials are used as paint thinners and in recent years
their composition has changed quite a lot as a result of pressure by the
Environmental Protection Agency and analogous state groups to reduce discharges
of photoreactive hydrocarbons to the ambient air.  Neither the aliphatic
hydrocarbons nor the lower aromatics (benzene, toluene, xylenes, etc.) are very
photoreactive and therefore, such compounds have begun to dominate as paint
thinners.  In addition, several ketones, alcohols, and esters have been used.

                                  SOLVENTS.TXT
                                     Page 9













                            Downloaded from FireNet Leader
                             (719) 591-7415  Dataline



     Thinners are mainly aliphatic hydrocarbons.  Of the aliphatics, hexane
stands out as by far the most toxic.  Chronic inhalation of hexane can cause
peripheral neuritis that can progress to neuropathy (death of sensory nerves in
the fingers, toes, etc.), and as a result, the TLV has been progressively
reduced in recent years.  In 1980, ACGIH announced an intent to reduce the
hexane TLV to 50 ppm and did so later, retaining the older value of 500 ppm for
the other C6 isomers.  The TLV for other aliphatics such as pentane, heptane,
and octane is still several hundred parts per million (300 ppm for octane, 400
for heptane, 600 for pentane).  When a mixture of aliphatic hydrocarbons is used
(as in paint thinners), the analytical problem can be formidable; one of the
ways of handling that problem is to express "total aliphatics" as if all were
hexane whether or not hexane itself is present, and then use a TLV of about 1450
mg/cu. m (that for octane) to evaluate the exposure.  This would be a hexane
equivalent of about 400 ppm.

     Aliphatic hydrocarbons other than hexane used in mineral spirits, VM&P
(varnish maker's and painter's) naphtha, etc. are capable of causing narcosis
(sleepiness) and perhaps some irritation if the exposure is excessive.


Perchloroethylene

     Tetrachloroethylene has long been known best as perchloroethylene or
"Perc."  This chlorinated solvent has its main uses in the dry cleaning industry
and as a metal degreaser.  Acutely it is a good narcotic with incoordination
being the first effect observed at relatively low concentrations.  Upon chronic
overexposure some liver and kidney injury may occur.  Gross skin contact can
result in skin burns and blisters.

     Mice fed maximum tolerated doses of this material developed hepatocellular
carcinomas (liver cancers) but this effect was not observed in rats.
Reproductive effects have been searched for but not found.

     The OSHA PEL for perchloroethylene currently is 100 ppm while the TLV is
50.  The former STEL of 100 ppm has recently been raised to 200 ppm.

     Perchloroethylene has no flash point or explosive limits in air.


n-Propyl Acetate

     Propyl acetate is much more of an irritant to the eyes than it is to the
respiratory tract.  At its TLV (and PEL) of 200 ppm, it will probably irritate
the eyes of the unacclimated; its STEL is 250 ppm.  At that concentration the
odor is pleasant.  No human systemic effects have been reported in the
literature although high concentrations can probably cause narcosis.  Eye
irritation, however, should act to prevent voluntary overexposure to

                                  SOLVENTS.TXT
                                     Page 10













                            Downloaded from FireNet Leader
                             (719) 591-7415  Dataline


concentrations that could prove injurious.


n-Propyl Alcohol

     Propyl alcohol (n-propanol) is irritating to the eyes and respiratory tract
in concentrations above about 400 ppm.  At higher concentrations it probably can
cause narcosis.  No systemic toxic effects from industrial exposure have been
reported in the literature.  Its TLV (and PEL) is 200 ppm with an STEL of 250
ppm.


Toluene

     Also called (incorrectly) "toluol," toluene is a fairly strong narcotic and
a mild respiratory tract irritant.  The ACGIH TLV for toluene is 100 ppm (parts
toluene vapor per million parts of air + vapor, by volume) with an STEL of 150
ppm.  The current OSHA Permissible Exposure Limit (PEL) for this material is 200
ppm.  NIOSH has recommended a Standard of 100 ppm with a "ceiling" of 200 ppm
for 10 minutes.

     Exposure to toluene for a few hours to a concentration twice the TLV (200
ppm) is likely to result in drowsiness and some deficit in manual coordination.
Effects from chronic exposure to such concentrations are likely to be similar to
those of a single exposure.  The chronic inhalation toxicity of toluene is about
the same as the acute (short term, single exposure) inhalation toxicity.

     Prolonged, repeated skin contact may result in defatting dermatitis.


Trichloroethylene

     Trichloroethylene (TCE) has the ability to cause narcosis (sleepiness)
following exposure to concentrations easily attained around a degreaser or when
the material is used as a "bucket solvent."  In fact, trichloroethylene has been
used as a surgical anesthetic.  If exposures are prolonged and repeated, then
some injury to the liver and perhaps kidneys can occur.  The TLV for TCE is 50
ppm with a STEL of 200 ppm; the OSHA PEL and the NIOSH Recommended Standard are
both 100 ppm.

     TCE in common with many halogenated solvents has no flash point but it does
have an explosive range in air and oxygen.  In air, concentrations in the range
of 10.5 to 90% can be made to explode.


1,1,1-Trichloroethane

     1,1,1-Trichloroethane is also called methyl chloroform and has several

                                  SOLVENTS.TXT
                                     Page 11













                            Downloaded from FireNet Leader
                             (719) 591-7415  Dataline


trade names, the most popular of which is "Chlorothene" (Dow Chemical).  1,1,1-
Trichloroethane is the least toxic of the chlorinated hydrocarbons.  From a
short-term (acute) exposure, the consequences of increasing the concentration
inhaled begin with more and more definite odor, then dizziness, followed by
disorientation, collapse, and then unconsciousness.  The consequences of chronic
(long term) overexposure are much the same because this material has little
ability to injure body organs such as the liver and the kidneys.  All three
standards-setting organizations (NIOSH, OSHA, and ACGIH) agree that
concentrations as high as 350 ppm (parts of the material per million parts of
air + material by volume) may be inhaled repeatedly, 8 hr/day, 40 hr/wk for a
working lifetime without ill effect.  ACGIH uses 450 ppm as the short-term
exposure limit (STEL).  The National Cancer Institute failed to cause any
cancers in mice and rats after feeding the maximum tolerated dose for about two
years.

     Methyl chloroform has an odor threshold of about 20 ppm and therefore, its
odor is perceptible in concentrations much lower than the TLV.  The current TLV
was chosen in part to avoid strong-smelling concentrations.  At 350 ppm the odor
is rather pleasant and ethereal.

     Although methyl chloroform has no flash point, a strong source of ignition
can explode vapor concentrations in the range of 10 to 15.5% in air (100 000 to
155 000 ppm).  All 1,1,1-trichloroethane is subject to decomposition (especially
when catalyzed) even in the liquid phase.  Inhibitors can quench such reactions
and prevent the material from "going acid" (the acid formed, HCl, may not
catalyze further decomposition, but several metallic chlorides such as those of
aluminum and iron do) and possibly undergoing a runaway breakdown.  Although
such is not a serious hazard in the usual solvent applications, it may be very
important when methyl chloroform is used in vapor-phase degreasing.


Xylene(s)

     Commercial xylene is a mixture of the three isomers of dimethyl benzene
with m-xylene predominating.  The mixture or any of its components may be called
(incorrectly) "xylol."

     All of the xylenes are similar in their toxic properties, both
qualitatively and quantitatively.  These materials are fairly strong narcotics
but are much more irritating to the eyes and upper respiratory tract than is
toluene.  That irritation is very noticeable at twice the 100 ppm TLV (and OSHA
PEL and NIOSH Recommended Standard), sufficiently so that the warning properties
of xylene are considered adequate to prevent voluntary overexposure to an extent
that narcosis is problem.  Prolonged overexposure may result in some gastric
distress along with mild and reversible blood changes.  In that manner the
chronic inhalation toxicity of xylene differs somewhat from the acute inhalation
toxicity.


                                  SOLVENTS.TXT
                                     Page 12













                            Downloaded from FireNet Leader
                             (719) 591-7415  Dataline


     Xylenes are more severe skin irritants than is toluene.  Prolonged contact
with the liquid may cause blistering in addition to typical defatting
dermatitis.































ay cause blistering in addition to typical defatting
dermatitis.














































                                  SOLVENTS.TXT
                                     Page 13






                                                                                                                        