Chapter 2 Guide to Chemical Hazards

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 foreseeabe 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 through 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 Toxic effects can be
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 Normally, single exposure is involved (e.g. exposure to hydrogen cyanide, carbon monoxide)

Toxicity Chronic poisoning Substances in combination
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 Allergens 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 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

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

* Refer to Appendix 2 for more examples
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

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

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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