SECTION 2:General Information
About Chemical Safety
The decisions you make concerning the use of chemicals in the laboratory
should be based on an objective analysis of the hazards, rather than merely
the perception of the risks involved. Once this has been accomplished,
a reasonable means of controlling the hazards through experimental protocol,
work practices, ventilation, use of protective clothing, etc., can be
In order to assess the hazards of a particular chemical, both the physical
and health hazards of the chemical must be considered.
The physical hazards of a chemical include its flammability, corrosivity and reactivity. Flammability is the tendency of a chemical to burn. The flashpoint, autoignition temperature and flammable limits of the material may be found in the material safety data sheet (MSDS), and are helpful in assessing the potential for a fire hazard under specified conditions. Corrosivity is a chemical’s potential to degrade materials by a chemical reaction. Corrosivity of acidic and basic liquids is measured by their pH, or concentration of (H+) protons. Reactivity is the potential of the material to explode or react violently with air, water or other substances upon contact. The MSDS furnishes this information in the Reactivity Data section.
Before using any chemical, the MSDS or other appropriate source should
be reviewed to determine what conditions of use might pose a hazard. Accidents
with hazardous chemicals can happen quickly and may be quite severe. The
key to prevention of these accidents is awareness. Once the hazards are
known, the risk of an accident may be significantly reduced by using safe
2A. Health Hazards of Chemicals
The health effects of hazardous chemicals are often less
clear than the physical hazards. Data on the health effects of chemical
exposure, especially from chronic exposure, are often incomplete. When
discussing the health effects of chemicals, two terms are often used
interchangeably - toxicity and hazard. However, the
actual meanings of these words are quite different. Toxicity
is an inherent property of a material, similar to its physical constants.
It is the ability of a chemical substance to cause an undesirable effect
in a biological system. Hazard is the likelihood that a material
will exert its toxic effects under the conditions of use. Thus,
with proper handling, highly toxic chemicals can be used safely. Conversely,
less toxic chemicals can be extremely hazardous if handled improperly.
RISK = TOXICITY X EXPOSURE
The health risk of a chemical is a function of the toxicity
and the exposure. No matter how toxic the material may be, there is
little risk involved unless it enters the body. An assessment of the
toxicity of the chemicals and the possible routes of entry will help
determine what protective measures should be taken.
Routes of Entry (top)
Skin and Eye Contact
The simplest way for chemicals to enter the body is through direct contact
with the skin or eyes. Skin contact with a chemical may result in a
local reaction, such as a burn or rash, or absorption into the bloodstream.
Absorption into the bloodstream may then allow the chemical to cause
toxic effects on other parts of the body. The MSDS usually includes
information regarding whether or not skin absorption is a significant
route of exposure.
The absorption of a chemical through intact skin is influenced by the
health of the skin and the properties of the chemical. Skin that is
dry or cracked or has lacerations offers less resistance. Fat-soluble
substances, such as many organic solvents, can easily penetrate skin
and, in some instances, can alter the skin’s ability to resist
absorption of other substances.
Wear gloves and other protective clothing to minimize skin exposure.
See Section 3, Personal Protective Equipment for
more information. Symptoms of skin exposure include dry, whitened skin,
redness and swelling, rashes or blisters, and itching. In the event
of chemical contact on skin, rinse the affected area with water for
at least 15 minutes, removing contaminated clothing while rinsing, if
Chemical contact with eyes can be particularly dangerous, resulting
in painful injury or loss of sight. Wearing safety glasses or chemical
splash goggles can reduce the risk of eye contact. Eyes that have been
in contact with chemicals should be rinsed immediately with water continuously
for at least 15 minutes. Contact lenses should be removed while rinsing—do
not delay rinsing to remove the lenses. Medical attention is necessary
if symptoms persist. See Section 1, Emergency Procedures,
for more information.
The respiratory tract is the most common route of entry for gases, vapors
and particles. These materials may be transported into the lungs and
exert localized effects, or be absorbed into the bloodstream. Factors
that influence the absorption of these materials may include the vapor
pressure of the material,
solubility, particle size, its concentration in the inhaled air, and
the chemical properties of the material. The vapor pressure describes
how quickly a substance evaporates into the air – higher concentrations
in air cause greater exposure in the lungs and greater absorption in
Most chemicals have an odor that is perceptible at a certain concentration,
referred to as the odor threshold. There is considerable individual
variability in the perception of odor. Olfactory fatigue may occur when
exposed to high concentrations or after prolonged exposure to some substances.
This may cause the odor to seem to diminish or disappear, while the
danger of overexposure remains.
Symptoms of over-exposure may include headaches, increased mucus production,
and eye, nose and throat irritation. Narcotic effects, including confusion,
dizziness, drowsiness or collapse, may result from exposure to some
substances, particularly to many solvents. In the event of exposure,
close containers, open windows or otherwise increase ventilation, and
move to fresh air. If symptoms persist, seek medical attention.
Volatile hazardous materials should be used in a well-ventilated area,
preferably a fume hood, to reduce the potential of exposure. Occasionally,
ventilation may not be adequate and a fume hood may not be practical,
necessitating the use of a respirator. The use of a respirator is subject
to prior review by EHS according to University policy, since the federal
Occupational Safety and Health Administration Respiratory Protection
Standard regulates their use. See Section 3, Personal
Protective Equipment for more information.
The gastrointestinal tract is another possible route of entry for toxic
substances. Although direct ingestion of a laboratory chemical is unlikely,
exposure may occur as a result of ingesting contaminated food or beverages,
touching the mouth with contaminated fingers, or swallowing inhaled
particles which have been cleared from the respiratory system. The possibility
of exposure by this route may be reduced by not eating, drinking, smoking,
or storing food in the laboratory, and by washing hands thoroughly after
working with chemicals, even when gloves were worn.
Direct ingestion may occur as a result of the outdated
and dangerous practice of mouth pipetting. In the event of accidental
ingestion, immediately go to McCosh Health Center or contact the Poison
Control Center, at 800-962-1253 for instructions. Do not induce vomiting
unless directed to do so by a health care provider.
The final possible route of exposure to chemicals is by injection.
Injection effectively bypasses the protection provided by intact skin
direct access to the bloodstream, thus, to internal organ systems. Injection
may occur through mishaps with syringe needles, when handling animals,
or through accidents with pipettes, broken glassware or other sharp
objects that have been contaminated with toxic substances.
If injection has occurred, wash the area with soap and water
and seek medical attention, if necessary. Cautious use of any sharp
object is always important. Substituting cannulas for syringes and wearing
gloves may also reduce the possibility of injection.
Toxic Effects Of Chemical
How a chemical exposure affects a person depends on many
factors. The dose is the amount of a chemical that actually enters the
body. The actual dose that a person receives depends on the concentration
of the chemical and the frequency and duration of the exposure. The
sum of all routes of exposure must be considered when determining the
In addition to the dose, the outcome of exposure is determined by (1)
the way the chemical enters the body, (2) the physical properties of
the chemical, and (3) the susceptibility of the individual receiving
Toxic Effects of Chemicals
The toxic effects of a chemical may be local or systemic.
Local injuries involve the area of the body in contact with the chemical
and are typically caused by reactive or corrosive chemicals, such as
strong acids, alkalis or oxidizing agents. Systemic injuries involve
tissues or organs unrelated to or removed from the contact site when
toxins have been transported through the bloodstream. For example, methanol
that has been ingested may cause blindness, while a significant skin
exposure to nitrobenzene may effect the central nervous system.
Certain chemicals may affect a target organ. For example, lead primarily
affects the brain, kidney and red blood cells; isocyanates may induce
an allergic reaction (immune system); and chloroform may cause tumors
in the liver and kidneys.
It is important to distinguish between acute and chronic
exposure and toxicity. Acute toxicity results from a single,
short exposure. Effects usually appear quickly and are usually reversible.
Chronic toxicity results from repeated exposure over a long
period of time. Effects are usually delayed and gradual, and may be
irreversible. For example, the acute effect of alcohol exposure (ingestion)
is intoxication, while the chronic effect is cirrhosis of the liver.
Acute and chronic effects are distinguished in the MSDS, usually with
more information about acute exposures than chronic.
Evaluating Toxicity Data
The toxicity of a chemical is usually expressed as the quantity
of the material or the dose required to exert a specific effect.
It is difficult to obtain useful data on chemical toxicity. Most estimates
of human toxicity are based on animal studies, which may or may not
relate to human toxicity. In most animal studies, the effect measured
is usually death. This measure of toxicity is often expressed as an
LD50 (lethal dose 50) – the dose required to kill 50% of the test
population. The LD50 is usually measured in milligrams of the material
per kilogram of body weight of the test animal. The concentration in
air that kills half of the population is the LC50. See Table 1 for examples.
Table 1: Toxicity Ratings Based on LD50
Lethal Dose based
on a 70 kg person
||A taste (7 drops or less)
||Arsenic trioxide, Strychnine
||Aspirin, Sodium chloride
To estimate a lethal dose for a human based on animal tests, the LD50
must be multiplied by the weight of an average person. Using this method,
it is evident that just a few drops of a highly toxic substance, such
as dioxin, may be lethal, while much larger quantities of a slightly
toxic substance, such as acetone, would be necessary for the same effect.
Very few chemicals have been evaluated for chronic effects, given the
complexity of that type of study. Chronic exposure may have very different
effects than acute exposure. Usually, studies of chronic exposure evaluate
its cancer causing potential or other long-term health problems.
Susceptibility of Individuals
Factors that influence the susceptibility of an individual to the effects
of toxic substances include nutritional habits, physical condition,
obesity, medical conditions, drinking and smoking, and pregnancy. Due
to individual variation and uncertainties in estimating human health
hazards, it is difficult to determine a dose of a chemical that is totally
Over a period of time, regular exposure to some substances can lead
to the development of an allergic rash, breathing difficulty, or other
reactions. This phenomenon is referred to as sensitization.
Over time, these effects may occur with exposure to smaller and smaller
amounts of the chemical, but will disappear soon after the exposure
stops. For reasons not fully understood, not everyone exposed to a sensitizer
will experience this reaction. Examples of sensitizers include epoxy
resins, nickel salts, isocyanates and formaldehyde.
Particularly Hazardous Substances
The OSHA Laboratory Standard defines a particularly hazardous substance
as “select carcinogens”, reproductive toxins, and substances
that have a high degree of acute toxicity. The Chemical Hygiene Plan
and Laboratory Safety Manual outline provisions for additional protection
when working with these agents, including establishment of a designated
area, use of containment devices such as a fume hood or glove box, procedures
for safe removal of contaminated waste, and decontamination procedures.
For more information on handling particularly hazardous substances,
contact your departmental Chemical Hygiene Officer or Section
7.10 of the Lab Safety Manual.
High Acute Toxicity (top)
Substances with high acute toxicity may be fatal or cause damage to
a target organ as a result of a single exposure or an exposure of short
duration. Examples include hydrogen cyanide, dimethylmercury, and diisopropyl
fluorophosphate. Special care must be taken when working with these
Many chemicals have been evaluated for their ability to cause cancer.
The latency period for most cancers ranges from twenty to forty years.
The risk of developing cancer from exposure to a chemical increases
with the length of exposure and with the exposure concentration.
It is important to understand the distinction between human
carcinogens and suspected human carcinogens.
The term human carcinogen is used when there is clear evidence
of the ability to cause cancer in humans. Suspected human carcinogen
refers to chemicals that have been shown to cause cancer in two or more
animal species and are therefore suspect in humans. Prudent behavior
dictates that a suspected human carcinogen be handled in the laboratory
the same as a known human carcinogen.
Anyone who works with, or plans to work with carcinogens or suspected
carcinogens must follow the guidelines outlined in the Particularly
Hazardous Substances section of the Lab Safety Manual. Lists of
known and suspected carcinogens may be found in the appendices of the
Lab Safety Manual. For a particular substance, the Toxicity Data
section of the Material Safety Data Sheet may be consulted to determine
whether or not the substance is considered a carcinogen by the Occupational
Safety and Health Administration (OSHA), the National
Toxicology Program (NTP) or the International
Association for Research on Cancer (IARC).
Reproductive Toxins (top)
Reproductive toxins are chemicals which affect the reproductive system,
including mutagens (those which cause chromosomal damage) and embryotoxins.
Embryotoxins may be lethal to the fertilized egg, embryo or fetus, may
be teratogenic (able to cause fetal malformations), may retard growth
or may cause post-natal functional deficiencies. Other reproductive toxins
may cause sterility or may affect sperm motility.
chemicals may cross the placenta, exposing the fetus. A developing fetus
may be more sensitive to some chemicals than its pregnant mother, particularly
during the first twelve weeks of pregnancy, when the mother may not
know she is pregnant. Proper handling of chemicals and use of protective
equipment is especially important to reduce fetal exposure to chemicals.
Known human teratogens include organic mercury compounds, lead compounds,
glycol ethers, ionizing radiation, some drugs, alcohol ingestion, and
cigarette smoking. Some substances that may cause adverse reproductive
effects in males include 1,2-dibromo-3-chloropropane, cadmium, mercury,
boron, lead, some pesticides, and some drugs. More than 800 chemicals
have been shown to be teratogenic in animal models - many of these are
suspected human teratogens. A partial list is included in the appendices
of the Laboratory Safety Manual.
Laboratory workers who are contemplating pregnancy or are pregnant should
review the toxicity of the chemicals in their laboratory and may consult
with the departmental Chemical Hygiene Officer or EHS to determine whether
any of the materials used in the laboratory pose additional risk during
pregnancy. EHS provides confidential counseling to help determine what
actions are recommended.
Where To Find Toxicity Information
Toxicity information may be found in Material Safety Data Sheets, under
the “Health Hazard Data” section, on product labels, in
the Registry of Toxic Effects of Chemical Substances (RTECS), or in
many other sources listed in the Health and Safety Reference Guide in
Appendix E. For more information,
contact Environmental Health and Safety at