chapter 2 guide to chemical hazards

Chapter 2Guide 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

fatalقاتل

• 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)


• 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


Examples on MSDS

Acetone

Nitric acid

Water


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)


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%


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”


• 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.


• 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)


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.


• 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.


• 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


• 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).


• 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.


• 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


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;


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


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;


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 fire1 - Slightly hazardous2 - Hazardous3 - Extreme danger4 - Deadly

Flammability Hazard 0 - Will not burn1 - Will ignite if preheated2 - Will ignite if moderately heated3 - Will ignite at most ambient conditions4 - Burns readily at ambient conditions

Reactivity Hazard 0 - Stable and not reactive with water1 - Unstable if heated2 - Violent chemical change3 - Shock and heat may detonate4 - 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


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.


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 ExamplesOxidizing agents Nitrates, permanganates,

chromatesReducing agents Hydrogen, carbon,

hydrocarbons, organic acidsCorrosive chemicals Strong and some weak acids

and bases, halogensWater-reactive chemicals Alkali metals, some hydrides,

phosphides, carbidesAir-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


Solvents and Their Hazards Examples of some solvents

• Water

• Organic solvents (methanol, hexane, ether): mostly

flammable

Flammable solvents do not burn; their vapor

burns


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


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


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


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


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


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


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


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


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 water-

wash-down laboratory hoods that has been designated

to be used only for this purpose


• 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


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

NO2O2N

OH

NO2


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


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)


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


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


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)


• 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


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


• 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


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


• 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


• 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


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

chapter 2 guide to chemical hazards

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