Chapter 2
Guide to Chemical Hazards
Chapter Outline
 Introduction
 Toxicity
 Source of Information
 The Properties of Chemicals
Introduction
 Chemicals and laboratory intruments
can harm you if not handled properly
Introduction
 Chemicals can be classified as
 Toxic
 Explosive
 Flamable
 Reactive
 Carcinogenic
Introduction
 Some chemicals can harm you in more than
one way
 Consider every chemical as hazardous
 Degree of hazard vary from one chemical to
another
Introduction
 Example: gasoline and alcohol
 Both are flammable, but gasoline is more
flammable
 Gasoline ignites easily, burn or explode more
vigorously than gasoline
Introduction
 Working with chemicals can be safe if
proper precautions are followed
 Your laboratory instructor will guide you on
how to work safely in the laboratory
Toxicity
“What is it that is not poison? All things are
poison and nothing is without poison. It is the
dose only that makes a thing not a poison.”
Paracelsus
Toxicity
 Any substance could be harmful to living
organisms
 Hazardous chemical: any chemical that presents
a hazard either under normal use or in a
foreseeable emergency (OSHA)
Toxicity
 Factors that affect toxicity are variable:
 Dose (amount of substance to which one is
exposedand the length of time of exposure to the
substance)
Toxicity
 Route of exposure
• Inhalation ‫استنشاق‬through lungs by breathing
• Ingestion through digestive system (eating, drinking,
chewing gum, smoking, applying cosmetics, using
contaminated beaker in lab for drinking, eating with
contaminated hands, etc…)
• Absorption through body opening (skin, eyes, ears) or
• Injection (e.g. contaminated sharp objects)
Route of exposure
Toxicity
 Other factors (e.g. gender, age, lifestyle, allergic
factors, genetic disposition, mode, …)
 Toxic effects can be
 immediate or delayed
 reversible or irreversible
 local or systematic
Toxicity
 Toxic effects may vary from
 Mild and reversible (e.g headache from inhaling
ethyl acetate that disappears with inhaling fresh
air,
 to Serious and irreversible (e.g. birth defects
from excessive exposure to a toxic chemical
during pregnancy or cancer from excessive
exposure to a carcinogen)
Toxicity
 Toxic effects can be:
 Acute poisoning
• Exposure to a toxic substance that lasts for  24 h
• Often, the effect is sudden, can be painful, severe, or
fatal ‫قاتل‬
• Normally, single exposure is involved (e.g. exposure to
hydrogen cyanide, carbon monoxide)
Toxicity
 Chronic poisoning
• Repeated esposures with time intervals in months or
years
• Symptoms may not be immediate (e.g. lead or mercury
poisoning, exposure to pesticides or radiation)
 Substances in combination
• 2 or more hazardous materials are present and the
cobined effect is greater than the effect of individual
substance
Toxicity
• Examples:
– exposure to alcohol and chlorinated solvents
(combined effect)
– Cyanide and amyl nitrite (antagonistic effect)
 Allergens
• Substances that produce immunologic reaction
– Asthma-like symptoms or dermatitis
Toxicity
 Generally, toxic effect from a substance is
dependent on sevirity of exposure
 more severe the results are expected from larger
/ more frequent exposure
 Minimizing exposure means reducing or
preventing harm. How to achieve this?
Toxicity
 Ways of Reducing Exposure
 Minimize exposure through ingestion
• Do not eat or drink in lab
• Do not put your hands or fingers in your mouth
• Wash your hands before leaving lab or if contaminated
• When in lab keep your hands away from your eyes,
ears, or nose unless you wash them
• Do not touch your skin if injured
• Be very careful when working with sharp objects
Toxicity
 Minimize exposure through skin
• Use proper gloves
• Discard gloves after use and wash your hands
 Minimize exposure through inhalation
• Labs should be well ventilated
• Use fume hoods/safety cabninets when necessary
 If a chemical is spilled on your clothes or skin
• Wash the affected area immediately and thoroughly
with running water
Sources of Information
 Material Safet Data Sheets (MSDS)
 MSDS describes the hazards of a chemical and
the precuations that must be taken to avoid harm
 MSDS should be made available in laboratories
for workers and students to read before carrying
out any experiment
Sources of Information -MSDS
 MSDS should at least contain
• Name of the hazardous chemical (names with % if
mixture)
• Some of physical and chemical properties (e.g. vapor
pressure, boiling point, flash point, density, …)
• Physical hazards of the substance (e.g. flammable,
explosive, corrosive, …)
• Health hazards (e.g. corrosive, irritant, carcinogen, …)
• Routes of entry (e.g. inhalation, ingestion)
Sources of Information -MSDS
• Exposure limits: permissible exposure limit (PEL) and
threshold limit value (TLV) if established
• Can the substance cause cancer or not
• Precautions to be taken when using the substance
• Control measures, work practices, and PPE
• Emergency and first aid procedures
• Date of preparation / revision
• Name of manufacturer and address
Sources of Information -MSDS
 Examples on MSDS
Acetone
Nitric acid
Water
Sources of Information -MSDS
 Understanding an MSDS
 CAS registry no: a unique number assigned to
each chemical by ACS CAS (Chemical Abstracts
Service)
 Ceiling limit: concentration in ppm or mg/m3 that
must not be exceeded in a specified time period
(typically 15 min)
Sources of Information -MSDS
 Chemical name: IUPAC, CAS, common chemical
name
• Example: 1,2-ethanediol (IUPAC) or ethylene glycol
(common)
 Composition of mixtures: includes all hazardous
components present in concentrations >1% and
all carcinogens in concentrations >0.1%
Sources of Information -MSDS
 Control measures: list types of PPE (e.g. lab
coats, glove, respiratory equipment) , fumehood,
glovebox, safety cabinit, etc…
 Fire and explosion hazard data:
• Flash point: “lowest temperature at which the vapor of
the chemical can be ignited by a flame when the
chemical is slowly heated in a special apparatus”
• Autoignition temperature: “lowest temperature at
which a chemical ignites spontaneously in the air”
Sources of Information -MSDS
• Flammable limits: volatile flammable chemicals have
min and max vapor concentrations in air below and
above which they cannot be ignited. Increase in
temperature decreases the lower flammable limit and
increases the upper limit. Increase in pressure
decreases the lower flammable limit and increases the
upper limit.
• Recommended extinguishing media: some chemicals
(e.g. Mg) ignites more vigorously when in contact with
water ro carbon dioxide.
Sources of Information -MSDS
• First Aid: describes procedures of emergency first aid.
Perform the first aid if qualified, call the ambalance.
• Health Hazard Data:
Lethal Dose Fifty (LD50)
Lethal concentration Fifty (LC50)
Sources of Information -MSDS
LD50 (lethal dose fifty) is the lethal single dose (usually by
ingestion) in mg of chemical per kg of animal body
weight that is expected to kill 50% of the test animal
population within a specified time.
LC50 (lethal concentration fifty) is the lethal concentration
of a chemical in air expressed as ppm of gases and
vapors or as mg/L of air for dusts and mists expected to
kill 50% of the test animal population within a specified
time by inhalation.
Sources of Information -MSDS
• Permissible exposure limit (PEL): concentration of a
hazadous chemical in the air in ppm or mg/m3. It is the
max concentration in the breathing air that can be
inhaled without harm by an adult worker for 8 h a day,
40 h a week, during his/her working lifetme – provided
that the worker is a person of average healt.
Sources of Information -MSDS
• Physical/chemical properties:
Boiling point
Melting point
Vapor pressure
Specific gravity
Solubility
Appearance and odor: liquid, solid, or gas (at
room temperature); color, crystalline, or
amorphous; etc..
Evaporation rate
Sources of Information -MSDS
• Precautions for spills and cleanup: describes how to
properly cleanup of a spill or release (can it be put in a
landfill or an approved disposal facility).
• Reactivity: some chemicals react vigorously with other
chemicals; others are self-reactive or unstable and
decompose vigorously if disturbed.
• Short-term exposure limit (STEL): concentration in ppm
or mg/m3 that should not be exceeded for more than a
short period (usually 15 minutes).
Sources of Information -MSDS
• Target organ: name of an organ(s) (kidney, liver, skin,
eyes, etc.) or system(s) (respiratory system, central
nervous system, etc.) that are likely to be adversely
affected by an overexposure to the chemical.
• Time-weighted average (TWA): worker’s exposures are
to be measured and averaged over an 8-hour day. If the
TWA does not exceed the PEL or TLV for a worker, then
he or she is not harmed.
Sources of Information -MSDS
• Threshold limit value (TLV): this number is a
concentration limit (similar to PEL). PEL limit is a legal
limit; the TLV limit is a voluntary, recommended limit.
Sources of Information - Labels
Sources of Information - Labels
 Lables on bottles of chemicals provide
critical information about the chemical
 Label should contain:
 name of the chemical;
 one of 3 signal words: Danger, Warning, or
Caution, to indicate the relative degree of
severity of the hazard(s) of the chemical;
Sources of Information - Labels
Danger: signifies that the hazards can cause
serious injury (e.g., blindness, loss of a limb)
or death.
Warning: signifies that the hazards can cause
less than serious injuries.
Caution: warns users to be careful when using,
handling, or storing the chemical
Sources of Information - Labels
 main foreseeable hazard(s) when used;
 precautionary measures that will protect users
from the harmful effects of those hazards;
 first aid instructions;
 instructions in case of fire, if applicable;
 methods to handle spills or leaks, if appropriate;
Sources of Information - Labels
 instructions if the chemical requires unusual
handling and storage procedures; and
 name, address, and telephone number of the
manufacturer or supplier
Hazards and their Ratings
Hazard Type
Hazard Rating
Health Hazard
0 - Ordinary combustible hazards in a fire
1 - Slightly hazardous
2 - Hazardous
3 - Extreme danger
4 - Deadly
Flammability Hazard
0 - Will not burn
1 - Will ignite if preheated
2 - Will ignite if moderately heated
3 - Will ignite at most ambient conditions
4 - Burns readily at ambient conditions
Reactivity Hazard
0 - Stable and not reactive with water
1 - Unstable if heated
2 - Violent chemical change
3 - Shock and heat may detonate
4 - May detonate
How to Read MSDSs and Labels
Pages 16 - 20
MSDS & Properties of Chemicals
 MSDS provide also other useful information
about chemicals (e.g. solubilities, volatility,
reactivity, classification of chemicals)
 Examples:
 Reactivity of Chemicals
MSDS & Properties of Chemicals
 Reactivity of Chemicals
• MSDS provides information on the incompatibility of
chemicals
• Example: adding acetic acid to an oxidizing agent (e.g.
chromic oxide, nitric acid, perchloric acid, potassium
permanganate) produces a vigorous reaction. If
reaction conditions are not minimized (e.g. quantity,
temperature) the reactioncould be disastrous.
• Acetic acid could not be stored near an oxidizing agent.
MSDS & Properties of Chemicals
 Differing solubilities in water
• Knowledge of differing solubilities in water and other
solvents helps you decide how to dissolve a substance
• Examples:
– All nitrates are soluble in water
– Some chlorides and sulfides are soluble in water
– Some of the insoluble chlorides are slightly soluble
in warm water
– Solubility of some sulfides varies depending on pH
Properties of Chemicals
 Classifying Hazardous Chemicals
 All chemicals are hazardous in one way or
another
 You must know the hazards of each chemical
before dealing with it
 To facilitate knowledge about hazards of
chemicals, chemicals are classified in groups
Class
Examples
Oxidizing agents
Nitrates, permanganates,
chromates
Reducing agents
Hydrogen, carbon,
hydrocarbons, organic acids
Corrosive chemicals
Strong and some weak acids
and bases, halogens
Water-reactive chemicals
Alkali metals, some hydrides,
phosphides, carbides
Air-reactive chemicals
Alkali metals
Highly toxic chemicals
Carcinogens, cyanides, phenol
Less toxic chemicals
Ethanol, n-hexane, acetic acid
Self-reactive chemicals
Picric acid, TNT, diazo
compounds
Incompatible pairs*
Acid vs base, oxidizing agent
vs reducing agent
* Refer to Appendix 2 for more examples
Properties of Chemicals
 Solvents and Their Hazards
 Examples of some solvents
• Water
• Organic solvents (methanol, hexane, ether): mostly
flammable
 Flammable solvents do not burn; their vapor
burns
Properties of Chemicals
 Solvents and Their Hazards
 More rate of vaporization produces more
flammable vapors
 Vaporization increases with temperature
 All flammable liquids and solids must be kept
away from oxidizers and ignition sources
Properties of Chemicals
 Vapors of all organic solvents are toxic
 Some symptoms from overexposure to organic
solvent vapors:
• dizziness, slurred speech, unconsciousness and, rarely,
death
 Some organic solvents can penetrate intact skin
and cause dryness and cracking
Properties of Chemicals
 Affected organs:
• central nervous system, liver, kidneys
 Some organic solvents (e.g., ethers, some non-
aromatic unsaturated cyclic hydrocarbons) can
form potentially explosive peroxides
• These solvents are particularly dangerous if they are
evaporated close to dryness
Properties of Chemicals
 Acids and Bases
 Corrosive: all strong acids and bases, some weak
acids, some slightly soluble bases
 Irreversibly destroy living tissue (e.g. eye, skin)
when come in contact with
 Distruction increaes with concentration and
contact time
• some acids/bases start damaging within 15 s of contact
Properties of Chemicals
 HX acids:
• aqueous solutions are toxic
• vapors are serious respiratory irritants
• HF’s vapors or aquous solutions are :
– Toxic
– Rapidly absorbed through the skin, penetrating
deeply and destroying the underlying tissues
– Contact with dilute HF is usually painless for
several hours, but then serious burns appear along
with adverse internal effects and extreme pain
– Be well prepared before using HF
Properties of Chemicals
 Sulfuric acid (H2SO4)
• Very strong dehydrating agent when concentrated
• Dilute solutions are oxidizing agents
• Fuming sulfuric acid is a strong oxidizing agent
• When preparing aqueous solutions
– always slowly add the acid to water while stirring
the mixture
– heat of the solution highly increases the
temperature of the solution and causes it to boil
and splatter
Properties of Chemicals
 Nitric acid (HNO3)
• Strong oxidizing agent
• Reacts more rapidly than sulfuric acid
• Dilute nitric acid causes the exposed skin to become
yellowish brown if not washed off completely
Properties of Chemicals
 Phosphoric acid (H3PO4) is a weak acid
• Highly viscous when concentrated
• Strong dehydrating agent
• When diluting the acid, always add the acid to water
slowly while stirring
• dilute solutions taste sweet (used as a sweetner in soft
drinks)
• Do not taste or swallow the phosphoric acid that is
available in the laboratory
Properties of Chemicals
 Perchloric acid (HClO4):
• Very powerful oxidizing agent, particularly at elevated
temperatures
• Reacts explosively with organic compounds and other
reducing agents
• Must be used only in a specially constructed waterwash-down laboratory hoods that has been designated
to be used only for this purpose
Properties of Chemicals
• Never work with perchloric acid on laboratory benches
made of combustible material (e.g. Wood)
• Keep perchloric acid bottles on glass or ceramic
secondary containment trays with edges that are high
enough to hold all the acid if the bottle breaks
• Always digest organic matter with nitric acid before
adding perchloric acid
• Do not mix sulfuric or phosphoric acid with perchloric
acid
Properties of Chemicals
 Picric Acid
• Dry acid is highly explosive
• To be used only when necessary
• Picric acid contents should be moistened before
opening the bottle (explosive peroxides may have
formed in the cap threads)
• Immerse old picric acid bottles in water and slowly
twist the cap to allow water to dissolve any crystals,
then add water to moisturize the picric acid
Properties of Chemicals
 Bases:
• Aalkali metal hydroxides and aqueous solutions of
ammonia are the most common bases
• Na and K hydroxides are strong bases and very
destructive to the skin and the eyes
• Be cautious when preparing concentrated solutions of
these bases (high temperature are produced that cause
boiling and splattering)
• Vapors of aqueous ammonia solutions are irritating and
toxic
Properties of Chemicals
 Examples of Toxic Materials
 Halogens:
• toxic oxidizing agents, especially F
• Cl is a strong oxidizing agent
• Br is a corrosive volatile liquid that causes serious burns
on skin contact (lachrymator (tear gas) and should be
used in a fume hood)
Properties of Chemicals
 Mercury
• Hg evaporates easily and fill the air with toxic vapors
• Its vapor is a cumulative poison
• Spilled Hg should be immediately and thoroughly
cleaned up using an special apparatus
• inform your instructor in case of a Hg spill
• Spilled Hg can be made nonvolatile by amalgamation
with zinc dust or tin powder
Properties of Chemicals
 Strong bases
• all are corrosive and can cause serious, destructive
chemical burns, including blindness
• Strong bases are insidious (no immediate pain even
with concentrated solution, pain starts after severe
damage)
• saturated solutions (even dilute) of strong bases, such
as Ca(OH)2, also are extremely corrosive
Properties of Chemicals
 Formaldehyde
• A colorless, water-soluble, pungent, and irritating gas
• Available as an aqueous solution of formaldehyde at
concentrations varying from 37 to 56% (formalin)
• Inhalation of formaldehyde vapors results in severe
irritation of the upper respiratory tract and lead to
edema (accumulation of body fluids under skin)
Properties of Chemicals
• Do not breathe formaldehyde vapors (may cause
cancer, results in severe eye irritation)
• Avoid contact of formaldehyde solution with skin
(causes sensitization and allergy)
• Formaldehyde should be used and handled only in a
designated laboratory fume hood
Properties of Chemicals
 Cyanides and nitriles
• Rapidly acting toxic substances via all routes
• Overexposures can be fatal
• A few inhalations of HCN can cause mental
deterioration; a few more can be fatal
• Some metal cyanides form HCN in aqueous solutions
or in the presence of acid
Properties of Chemicals
• Before working with cyanides, you must have amyl
nitrite pearls handy as a first aid antidote
• Names of physicians who can treat overexposures to
cyanide and can administer sodium nitrite and sodium
thiosulfate solutions should also be available
Properties of Chemicals
 Organic Peroxides and Peroxide Formers
• Organic peroxides are usually unstable and extremely
flammable
• Peroxides are among the most dangerous chemicals
normally handled in laboratories
• Extremely sensitivite to shock, sparks, heat, friction, and
strong oxidizing and reducing agents and therefore
explode violently
• Peroxides have a specific half-life (rate of decomposition)
ETHER
Properties of Chemicals
• Never open a container if you suspect that it has
peroxide (may explode)
 The following compounds form peroxides
• Aldehydes
• Ethers (e.g. cyclic ethers, ethers derived from primary
and secondary alcohols)
• Compounds containing benzylic hydrogen atoms (e.g.
isopropyl benzene)
• Compounds containing the allylic (CH2= CHCH2–)
structure, including most alkenes
Properties of Chemicals
• Ketones, especially cyclic ketones
• Vinyl and vinylidene compounds (e.g., vinyl acetate and
vinylidene chloride)
 Containers of ethyl or isopropyl ether must be
labled with the date they are received, they must
be destroyed within 3 months after receipt
 Never distill an ether unless it is known for
certain to be free of peroxides, and even then do
not distill to dryness
Properties of Chemicals
 Examples of chemicals that can form dangerous
concentrations of peroxides when exposed to air
• Cyclohexene
• Cyclooctene
• Decalin (decahydronaphthalene)
• p-Dioxane
• Ethyl ether
• Isopropyl ether
• Tetrahydrofuran (THF)
• Tetralin (tetrahydronaphthalene