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Chapter 2Guide to Chemical HazardsChapter OutlineIntroductionToxicitySource of InformationThe Properties of Chemicals

IntroductionChemicals and laboratory intruments can harm you if not handled properly

IntroductionChemicals can be classified asToxicExplosiveFlammableReactiveCarcinogenic

IntroductionSome chemicals can harm you in more than one wayConsider every chemical as hazardousDegree of hazard vary from one chemical to another

IntroductionExample: gasoline and alcoholBoth are flammable, but gasoline is more flammableGasoline ignites easily, burn or explode more vigorously than alcohol

IntroductionWorking with chemicals can be safe if proper precautions are followedYour laboratory instructor will guide you on how to work safely in the laboratory

ToxicityWhat 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

ToxicityAny substance could be harmful to living organismsHazardous chemical: any chemical that presents a hazard either under normal use or in a foreseeable emergency (OSHA)

ToxicityFactors that affect toxicity are variable:Dose (amount of substance to which one is exposed and the length of time of exposure to the substance)

ToxicityRoute of exposureInhalation through lungs by breathingIngestion 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

ToxicityOther factors (e.g. gender, age, lifestyle, allergic factors, genetic disposition, mode, )Toxic effects can be immediate or delayedreversible or irreversiblelocal or systemic

ToxicityToxic effects may vary fromMild and reversible (e.g headache from inhaling ethyl acetate that disappears when 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)

ToxicityToxic effects can be:Acute poisoningExposure to a toxic substance that lasts for 24 hOften, the effect is sudden, can be painful, severe, or fatalNormally, single exposure is involved (e.g. exposure to hydrogen cyanide, carbon monoxide)

ToxicityChronic poisoningRepeated exposures with time intervals in months or yearsSymptoms may not be immediate (e.g. lead or mercury poisoning, exposure to pesticides or radiation)Substances in combination2 or more hazardous materials are present and the combined effect is greater than the effect of individual substance

ToxicityExamples:exposure to alcohol and chlorinated solvents (combined effect)Cyanide and amyl nitrite (antagonistic effect)AllergensSubstances that produce immunologic reactionAsthma-like symptoms or dermatitisToxicityGenerally, toxic effect from a substance is dependent on severity of exposuremore severe the results are expected from larger / more frequent exposureMinimizing exposure means reducing or preventing harm. How to achieve this?

ToxicityWays of Reducing ExposureMinimize exposure through ingestionDo not eat or drink in labDo not put your hands or fingers in your mouthWash your hands before leaving lab or if contaminatedWhen in lab keep your hands away from your eyes, ears, or nose unless you wash themDo not touch your skin if injured Be very careful when working with sharp objects

ToxicityMinimize exposure through skinUse proper glovesDiscard gloves after use and wash your handsMinimize exposure through inhalationLabs should be well ventilatedUse fume hoods/safety cabinets when necessaryIf a chemical is spilled on your clothes or skinWash the affected area immediately and thoroughly with running water

Sources of InformationMaterial Safety Data Sheets (MSDS)MSDS describes the hazards of a chemical and the precautions that must be taken to avoid harmMSDS should be made available in laboratories for workers and students to read before carrying out any experiment

Sources of Information -MSDSMSDS should at least containName 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 -MSDSExposure limits: permissible exposure limit (PEL) and threshold limit value (TLV) if establishedCan the substance cause cancer or notPrecautions to be taken when using the substanceControl measures, work practices, and PPEEmergency and first aid proceduresDate of preparation / revisionName of manufacturer and addressSources of Information -MSDSExamples on MSDS

Acetone

Nitric acid

Water

Sources of Information -MSDSUnderstanding an MSDSCAS 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 -MSDSChemical 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 -MSDSControl measures: list types of PPE (e.g. lab coats, glove, respiratory equipment) , fumehood, glovebox, safety cabinet, etcFire 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 apparatusAutoignition temperature: lowest temperature at which a chemical ignites spontaneously in the airSources of Information -MSDSFlammable 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 or carbon dioxide.

Sources of Information -MSDSFirst Aid: describes procedures of emergency first aid. Perform the first aid if qualified, call the ambulance.Health Hazard Data: Lethal Dose Fifty (LD50) Lethal concentration Fifty (LC50)

Sources of Information -MSDSLD50 (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 -MSDSPermissible 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 health. Sources of Information -MSDSPhysical/chemical properties: Boiling pointMelting pointVapor pressureSpecific gravitySolubilityAppearance and odor: liquid, solid, or gas (at room temperature); color, crystalline, or amorphous; etc..Evaporation rate

Sources of Information -MSDSPrecautions 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 -MSDSTarget 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): workers 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 -MSDSThreshold 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 - LabelsLabels on bottles of chemicals provide critical information about the chemicalLabel 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 - LabelsDanger: 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 - Labelsmain 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 - Labelsinstructions if the chemical requires unusual handling and storage procedures; and name, address, and telephone number of the manufacturer or supplier

Hazards and their RatingsHazard TypeHazard RatingHealth Hazard0 - Ordinary combustible hazards in a fire1 - Slightly hazardous2 - Hazardous3 - Extreme danger4 - DeadlyFlammability Hazard0 - Will not burn1 - Will ignite if preheated2 - Will ignite if moderately heated3 - Will ignite at most ambient conditions4 - Burns readily at ambient conditionsReactivity Hazard0 - Stable and not reactive with water1 - Unstable if heated2 - Violent chemical change3 - Shock and heat may detonate4 - May detonateHow to Read MSDSs and LabelsPages 16 - 20

MSDS & Properties of ChemicalsMSDS provide also other useful information about chemicals (e.g. solubilities, volatility, reactivity, classification of chemicals)Examples:Reactivity of Chemicals

MSDS & Properties of ChemicalsReactivity of ChemicalsMSDS provides information on the incompatibility of chemicalsExample: 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 ChemicalsDiffering solubilities in waterKnowledge of differing solubilities in water and other solvents helps you decide how to dissolve a substanceExamples: All nitrates are soluble in waterSome chlorides and sulfides are soluble in waterSome of the insoluble chlorides are slightly soluble in warm waterSolubility of some sulfides varies depending on pH

Properties of ChemicalsClassifying Hazardous ChemicalsAll chemicals are hazardous in one way or anotherYou must know the hazards of each chemical before dealing with itTo facilitate knowledge about hazards of chemicals, chemicals are classified in groups

ClassExamplesOxidizing agentsNitrates, permanganates, chromatesReducing agentsHydrogen, carbon, hydrocarbons, organic acidsCorrosive chemicalsStrong and some weak acids and bases, halogensWater-reactive chemicalsAlkali metals, some hydrides, phosphides, carbidesAir-reactive chemicalsAlkali metalsHighly toxic chemicalsCarcinogens, cyanides, phenolLess toxic chemicalsEthanol, n-hexane, acetic acidSelf-reactive chemicalsPicric acid, TNT, diazo compoundsIncompatible pairs*Acid vs base, oxidizing agent vs reducing agent* Refer to Appendix 2 for more examples

Properties of ChemicalsSolvents and Their HazardsExamples of some solventsWaterOrganic solvents (methanol, hexane, ether): mostly flammableFlammable solvents do not burn; their vapor burns

Properties of ChemicalsSolvents and Their HazardsMore rate of vaporization produces more flammable vaporsVaporization increases with temperatureAll flammable liquids and solids must be kept away from oxidizers and ignition sources

Properties of ChemicalsVapors of all organic solvents are toxicSome symptoms from overexposure to organic solvent vapors:dizziness, slurred speech, unconsciousness and, rarely, deathSome organic solvents can penetrate intact skin and cause dryness and cracking

Properties of ChemicalsAffected organs: central nervous system, liver, kidneysSome organic solvents (e.g., ethers, some non-aromatic unsaturated cyclic hydrocarbons) can form potentially explosive peroxidesThese solvents are particularly dangerous if they are evaporated close to dryness

Properties of ChemicalsAcids and BasesCorrosive: all strong acids and bases, some weak acids, some slightly soluble basesIrreversibly destroy living tissue (e.g. eye, skin) when come in contact withDestruction increases with concentration and contact timesome acids/bases start damaging within 15 s of contact

Properties of ChemicalsHX acids:aqueous solutions are toxicvapors are serious respiratory irritantsHFs vapors or aquous solutions are : ToxicRapidly absorbed through the skin, penetrating deeply and destroying the underlying tissuesContact with dilute HF is usually painless for several hours, but then serious burns appear along with adverse internal effects and extreme painBe well prepared before using HF

Properties of ChemicalsSulfuric acid (H2SO4) Very strong dehydrating agent when concentratedDilute solutions are oxidizing agentsFuming sulfuric acid is a strong oxidizing agentWhen preparing aqueous solutionsalways slowly add the acid to water while stirring the mixtureheat of the solution highly increases the temperature of the solution and causes it to boil and splatter

Properties of ChemicalsNitric acid (HNO3)Strong oxidizing agentReacts more rapidly than sulfuric acidDilute nitric acid causes the exposed skin to become yellowish brown if not washed off completely

Properties of ChemicalsPhosphoric acid (H3PO4) is a weak acidHighly viscous when concentratedStrong dehydrating agentWhen diluting the acid, always add the acid to water slowly while stirringdilute solutions taste sweet (used as a sweetner in soft drinks)Do not taste or swallow the phosphoric acid that is available in the laboratoryProperties of ChemicalsPerchloric acid (HClO4):Very powerful oxidizing agent, particularly at elevated temperaturesReacts explosively with organic compounds and other reducing agentsMust be used only in a specially constructed water-wash-down laboratory hoods that has been designated to be used only for this purpose

Properties of ChemicalsNever 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 breaksAlways digest organic matter with nitric acid before adding perchloric acidDo not mix sulfuric or phosphoric acid with perchloric acidProperties of ChemicalsPicric AcidDry acid is highly explosiveTo be used only when necessaryPicric 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 ChemicalsBases:Aalkali metal hydroxides and aqueous solutions of ammonia are the most common basesNa and K hydroxides are strong bases and very destructive to the skin and the eyesBe 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 ChemicalsExamples of Toxic MaterialsHalogens:toxic oxidizing agents, especially FCl is a strong oxidizing agentBr 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 ChemicalsMercuryHg evaporates easily and fill the air with toxic vaporsIts vapor is a cumulative poisonSpilled Hg should be immediately and thoroughly cleaned up using an special apparatusinform your instructor in case of a Hg spillSpilled Hg can be made nonvolatile by amalgamation with zinc dust or tin powder

Properties of ChemicalsStrong 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 ChemicalsFormaldehydeA colorless, water-soluble, pungent, and irritating gasAvailable 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 ChemicalsDo 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 ChemicalsCyanides and nitrilesRapidly acting toxic substances via all routesOverexposures can be fatalA 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 ChemicalsBefore working with cyanides, you must have amyl nitrite pearls handy as a first aid antidoteNames of physicians who can treat overexposures to cyanide and can administer sodium nitrite and sodium thiosulfate solutions should also be available

Properties of ChemicalsOrganic Peroxides and Peroxide FormersOrganic peroxides are usually unstable and extremely flammablePeroxides are among the most dangerous chemicals normally handled in laboratoriesExtremely sensitivite to shock, sparks, heat, friction, and strong oxidizing and reducing agents and therefore explode violentlyPeroxides have a specific half-life (rate of decomposition)

ETHER

Properties of ChemicalsNever open a container if you suspect that it has peroxide (may explode)The following compounds form peroxidesAldehydesEthers (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 ChemicalsKetones, especially cyclic ketonesVinyl 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 receiptNever distill an ether unless it is known for certain to be free of peroxides, and even then do not distill to dryness

Properties of ChemicalsExamples of chemicals that can form dangerous concentrations of peroxides when exposed to airCyclohexeneCycloocteneDecalin (decahydronaphthalene)p-DioxaneEthyl etherIsopropyl etherTetrahydrofuran (THF)Tetralin (tetrahydronaphthalene