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Chapter 5: Physical Hazards Section 5.1.1 Introduction to Corrosive Hazards

Chapter 5: Physical Hazards Section 5.1.1 Introduction to Corrosive Hazards Incident 5.1.1.1 Sulfuric Acid Spill Corrosives Destroy Skin Corrosive = chemicals that cause injury by damaging/destroying tissue on exposure Can be solids, liquids, gases, or solutions

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Chapter 5: Physical Hazards Section 5.1.1 Introduction to Corrosive Hazards

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  1. Chapter 5: Physical Hazards Section 5.1.1 Introduction to Corrosive Hazards Incident 5.1.1.1 Sulfuric Acid Spill Corrosives Destroy Skin Corrosive = chemicals that cause injury by damaging/destroying tissue on exposure Can be solids, liquids, gases, or solutions Limit Exposure: goggles, gloves, lab coat Use bottle carriers when transporting: rubber containers to prevent breaking bottles Know location of/how to use eye wash station and safety shower Use fume hood for corrosive gases: concentrated HNO3, HCl fume

  2. Safe Handling of Acids Corrosiveness of Acids is Variable Depend on: structure, tissue exposed, concentration, duration, temperature Use low concentrations and low temperatures if possible Wash off immediately to lower duration of exposure Strong Acids in Introductory Labs: HCl(aq) -------> H+(aq) + Cl-(aq) (100%) Use HCl if you need H+ and don’t mind Cl- H2SO4 is used to avoid Cl- (may precipitate some ions, oxidizes to Cl2) • Strong dehydrating agent: part of how it effects skin • Strongly exothermic (produces heat) when mixed with water HNO3 is the most toxic of these acids • Strong oxidizing agent • Produces toxic NOx gases Concentrations > 1M are usually corrosive Damage proteins by forming “coagulum” Coagulum may block further damage to underlying tissues Acids may be less damaging than bases due to this Concentrated Acids = as much as can dissolve in water, usually how purchased Dilute acids using the “A & W Rule”: pour acids into water Opposite procedure may cause acid to boil and splash on you

  3. Safe Handling of Bases NaOH (caustic soda; lye); KOH (caustic potash, lye); NH4OH (mostly NH3) NaOH and KOH are white solid pellets Strong Bases: NaOH(aq) -------> Na+(aq) + OH-(aq) (100% dissociation) Caustic in solid form or liquid solutions (Caustic = Corrosive) Generates a lot of heat when you dissolve the solid in water Can absorb water from air or your hand and make a concentrated solution Aqueous NH3 is a weak base: NH3(aq) + H2O(l) NH4+(aq) + OH-(aq) (~0.1%) Still corrosive Releases NH3 gas Irritating to eyes/membranes Damage to Tissues May not be immediately painful like an acid Saponification of lipids damages the molecules in skin: slick feel; makes soap No protective layer is formed, so base will continue to damage deeper 0.016 M

  4. Eyes and Corrosives Eyes aren’t affected in pH 3-10 range Eye’s epithelium is rapidly destroyed outside this pH range (strong acid/bases) Sulfuric Acid is particularly corrosive due to dehydrating effect and heat released Every second counts in washing the corrosive away if it contacts your eye Wash with water in eye wash station for at least 15 minutes Immediately get to an ER for evaluation by a doctor Inhalation of Corrosives: USE FUME HOODS! Corrosive gases can be inhaled, or even formed from other gases in the lungs NO2(g) + H2O(l) -------> HNO3(aq) Vapor pressure of NH3(g) over 6M NH4OH is 0.1atm = 100,000ppm IDLH value for NH3 is 300ppm (IDLH = immediately dangerous to life or health) LClo for 5 minutes exposure for mammals is 5000ppm Oxidizing Agents: very reactive with tissues; react to oxidize your biomolecules HNO3 (and NO3- salts) strong oxidizers as well as strong acid (corrosive) HOOH (hydrogen peroxide): 3% = disinfection; 30% = corrosive, strong oxidizer KMnO4 (potassium permanganate) = purple solution; indicator; corrosive/oxidizing

  5. Section 5.2.1 Corrosives in Advanced Labs Incident 5.2.1.1 Triflouroacetic Acid-HF Burn The Chemistry of Corrosive Compounds Oxidation/Reduction reactions with Nitric Acid HNO3 has N at the +5 oxidation state and Cu(s) is at 0 oxidation state NO2 has N at the +4 oxidation state (reduced) and Cu2+ is at +2 (oxidized) The oxidizing power of the oxidizer is influenced (raised) by higher concentration Aqua Regia = 3:1 mixture of concentrated HCl and HNO3: will even dissolve gold Other acids are corrosive power due to high [H+] concentrations Proteins are destroyed (cut into pieces) Other organic molecules are also destroyed or modified Bases catalytically cleave proteins and esters in fats by hydrolysis reactions

  6. Acids Common in Advanced Labs Acetic Acid Can be purified as “Glacial Acetic Acid” (fridge freezes 16.7oC to white solid) Flammable at concentrations > 50% Strong Dehydrating Agent: enough heat generated to cause burns Volatile and vapors can cause damage to lungs Phosphoric Acid (H3PO4) Weak acid, but can be found pure (not in water solution) Strong corrosive and causes severe burns to skin in concentrated forms Is irritating to the lungs, but usually does not cause pulmonary edema Hydrofluoric Acid (HF) Weak acid in water, yet highly corrosive if > 0.01 M If exposed, flush with water for only 5 minutes, then get medical help quick Calcium Gluconate or Benzalkonium Chloride are antidotes for burns Don’t work with HF unless the agents are available in the lab Many famous Fluorine Chemists (use HF) are missing fingers!

  7. 4. The Halogens: Oxidizing Agents (F2, Cl2, Br2, I2) Reaction: X2 + 2e- -------> 2X- F2 is exceptionally dangerous and can oxidize almost anything (rarely used) Cl2 was the first Weapon of Mass Destruction; Chemical Weapon in WWI 1000ppm airborne concentration (0.001 atm) for a few breaths is fatal Greenish colored gas released by artillery shells Br2 is a volatile (175 mm Hg vapor pressure) brown liquid Painful and destructive upon contact with skin or eyes Lachrymator (tears) at around 1ppm; Fatal at 1000ppm I2 is a purple volatile solid (0.3 mm Hg) Disinfectant to sanitize water Brown 8% concentration in ethanol “tincture of iodine” used to clean wounds Vapor is irritating and mildly corrosive; can be fatal at high concentrations 5. Phenol: complex toxicant behavior from a simple molecule Corrosive, toxic, rapidly absorbed through skin Local anesthetic: can’t feel it burning you (might smell it: 0.06ppm odor) Chloraseptic = 1% solution has antiseptic properties

  8. Other Dehydrating Agents and Water Reactive Compounds Sodium: Na + 2H2O -------> 2 NaOH + H2 (flammable) NaH (Sodium Hydride), LiAlH4 (Lithium Aluminum Hydride) Common Reducing Agents Produce H2 (flammable) and are corrosive Drying Agents: used to remove water from organic solvents (after extraction) Reactive with water CaO, P2O5 (P4O10) react strongly with water and become corrosive Response: scrape off any solid, wash with plenty of water, seek medical attention Working with Corrosives Wear gloves and lab coats to cover skin Nitrile gloves are generally effective Clean up spills: Keep others away Report the spill to instructors Use an appropriate spill kit

  9. Section 5.1.2 Flammables Incident 5.1.2.1 Sodium-Solvent Fire Using Flammables Everyday use: gasoline for your car and propane for you grill Very useful in the lab as well Flammable Chemical = easily ignite and rapidly burn, release much heat Once ignited, they will burn until all of the fuel is gone Come in gases, liquids, and solids: most often solvents for reactions Common: Acetone, Ethanol, Diethyl Ether, Ethyl Acetate, Hexane, Toluene Combustibles: ignite slower, but burn readily

  10. Characteristics of Flammables and Combustibles Boiling Point is usually relatively low (temperature gas in equilibrium with liquid) Flash Point = lowest temperature vapor near surface can be ignited Autoignition Temperature = temperature of spontaneous ignition (not usual in lab) Flammability Limits = range of vapor concentrations which supports fire/ignition Lower Explosive Limit (LEL) = lowest % by volume required for explosion Upper Explosive Limit (UEL) = highest % by volume to support fire (need O2) LEL (1-4%) and UEL (6-20%) common (Acetylene 2.5%--81%, very dangerous) Fire Hazard Rating System: different numbers, but SAME INFORMATION TO YOU United Nation’s Globally Harmonized System (GHS) uses chemical properties National Fire Protection Association (NFPA) uses the opposite order of numbers

  11. Review of How Fires Burn Fire Tetrahedron: all parts needed for fire Remove any of the four, fire will go out If using a flammable solvent: Search for and remove sources of ignition • Bunsen burner going • Sparks from electrical sources • Sparks from pouring from metal containers (Static electricity) It’s the vapors that burn, not the liquid • Vapors from spill can catch fire • Work in a hood to remove vapors Recognize the Flammable Solvent • Ether: particularly dangerous; Low Flash Point • Compare to common fuels

  12. Chemical Structure and Flammability Methanol (CH3OH) vs. Dichloromethane (CH2Cl2) Carbon in methanol has 3 H’s which can be replaced by oxygen (oxidation) CH2Cl2 only has 2 H’s left to react (less reactive toward oxidation = burning) Similar size and volatility CH3OH vs. CH3CH2OH vs. CH3CH2CH2OH vs. CH3CH2CH2CH2OH As molecular weight goes up, flammability goes down • Boiling point goes up with MWt • Flash point goes up with MWt • Vapor Pressure goes down with MWt D. Section 5.2.2 The Chemistry of Fire and Explosion 1. Incident 5.2.2.1 Ether Fire

  13. Fires are Chemical Reactions Oxidizable material, plus oxidizing agent (usually O2) makes heat and light Exothermic Reactions = Heat is released Complete Combustion = fuel is oxidized fully; requires excess O2 Incomplete Combustion = fuel is not fully oxidized; O2 is limited Dangers of Fires Heat is released Flashover = heat released ignites other material without flames touching it Small fire can quickly turn into a large fire if flashover occurs Flashover Temps: 480-650 oC (900-1200 oF) CO ignition (609 oC) contributes to flashover Toxic by-products are generated: many new chemicals produced by oxidation CO2 = simple asphyxiant; CO = chemical asphyxiant

  14. Smoke = mixture of gases and particulates; impedes lung function Gases: HCN, HCl, NOx (particularly from plastics) Consumption of Oxygen Physiological function is impaired as the O2 concentration decreases Usually, smoke inhalation is deadly before death is cause by lack of O2 Steam generated by water used to fight fire displaces O2 • Steam acts as a simple asphyxiant • Steam also helps “smother” the fire • Steam can burn skin; firefighters must cover all exposed skin iv. Backdraft: fire extinguishes itself at 16% O2; explodes when door opened

  15. Lab Gas Supplies and Fires Natural gas (methane, CH4) is often plumbed into lab for Bunsen burners, etc… Methane is extremely flammable: GHS = 1; NFPA = 4 LEL = 4.5% and UEL = 16.5% Must make sure to turn off all gas valves after use: leak could result in a fire Odorant gas (ethanethiol, CH3CH2SH) added to alert you Many modern labs have a main gas shutoff valve to activate when evacuating a fire Explosions from Fires Explosion = sudden release of energy as heat and light Energy released faster than can be dissipated by convection and heat capacity Shock wave at supersonic velocity is formed = wave of high pressure gas that can do considerable damage Requires flammable vapors in concentration between LEL and UEL + ignition BLEVE (“blev-ee”) = boiling liquid expanding vapor explosion Container of flammable liquid (solvent) is heated to failure due to pressure Rapid release of flammable vapors that are ignited instantly Sealed bottle in a lab fire: PV=nRT 300K to 1300K, Pressure goes from 1atm to 4.3 atm Can autoignite, or be ignited by the fire which caused it to fail

  16. Section 5.2.3 Incompatibles Incident 5.2.3.1 Exploding Hazardous Waste A Chemical Overview of Incompatibles Incompatible Chemicals = combination of substances that react violently with each other to potentially produce explosions and/or toxic substances Often unanticipated reactions occur—we aren’t prepared, may be no one around Incompatibles at low concentration can be mixed on purpose: we are prepared Not possible to memorize all possible combinations of incompatible chemicals Fundamental Chemistry can alert us to structures of incompatible partners Most exothermic reactions are acid/base or oxidation/reduction. Ask yourself: Is this a strong acid? Is this a strong base? Is this easily oxidized? Is this easily reduced?

  17. Acid-Base Incompatibles Most common in laboratories Strong Acid + Strong Base = very exothermic reaction Common Strong Acids: HCl, HNO3, H2SO4, HClO4, HBr, HI Common Strong Bases: NaOH, KOH, Ca(OH)2, LiOH, RbOH, CsOH Lower concentrations tend to make the reaction safer: less reactant, more water Other common Acid/Base Incompatible Reactions

  18. Strong Oxidants and Reductants—Redox Incompatibles Must identify compounds that are easily oxidized or reduced Good Oxidizing Agent gets Reduced Easily (large positive Eo) F2 is easily reduced; it is a strong Oxidizing Agent Good Reducing Agent gets Oxidized Easily (large negative Eo) Li(s) is easily oxidized; it is a strong Reducing Agent

  19. Trends Oxidizing Agents: elemental halogens, high oxidation state elements • F2 (F is 0, but really wants to be -1) • HNO3 (N is +5) [Involved in the majority of Redox Incompatible Rxns] • MnO4- (Mn is +7) • HOOH (O is -1, but really wants to be -2) Reducing Agents: active metals (alkali), H in the -1 oxidation state (hydride) • Li(s) (Li is 0, really wants to be +1) • H- is -1, but really wants to be 0 or +1 Anions with multiple oxygens and central atoms at high oxidation states are good oxidizers: ClO4- (particularly explosive), CrO4-, NO3-, etc… Organic compounds are often easily oxidized (C is 0, can become +4) Unanticipated Example: HNO3 + CH3COOH (nitric acid + acetic acid) REDOX

  20. Water-Reactives Water is usually non-reactive and safe, but some chemicals react with it violently Alkali metals often used to “dry” organic solvents (on NRC’s Dirty Dozen list) When “used up” the drying agent is destroyed using ROH If not all used up, or ROH added too quickly, fires can result (esp. w/ solvents) Special techniques in advanced chemistry labs for handling water reactive solutions Glovebox: controlled atmosphere with no water (or O2) Schlenk Line: all operations done under vacuum or inert gas Concentrated H2SO4: very exothermic reaction when mixed with water

  21. Pyrophorics = chemicals that ignite spontaneously in air Oxidized by O2 in air or react very quickly with H2O in air Some finely divided metal powders: Zn(dust) + H2O(l) -----> Zn(OH)2(s) + H2(g) LiAlH4 (on NRC’s Dirty Dozen list) LiAlH4(s) + 4H2O(l) -----> LiOH(aq) + Al(OH)3(s) + 4H2(g) Also purchased in solution of organic solvent (THF or Ether) FLAMMABLE! Boranes (BxHy) are boron equivalents to hydrocarbons Explored as possible rocket propellants Thermodynamic stability of the oxides produced lead to exothermicity B2H6 + 3O2 -----> B2O3 + 3H2O Silanes (SixHy) are silicon equivalents to hydrocarbons Thermodynamic stability of the oxides produced lead to exothermicity SiH4 + 2O2 -----> SiO2 + 2H2O Elemental Phosphorous i. Phosphorous only appears as its oxides in nature; we can make elemental form The allotrope “white phosphorous” = P4 tetrahedron that reacts with air P4 + 5O2 -----> P4O10 Stored under water to prevent interaction with oxygen When working with pyrophorics: Know What You are Doing, and Have a Plan

  22. Storing Incompatibles Incompatible chemicals should not be stored together This is especially important in earthquake active locations Tornadoes (or other weather) can still end up breaking bottles Minimize the amount of chemicals you store in the lab (of any kind) Section 5.3.1 Gas Cylinders and Cryogenic Liquids Incident 5.3.1.1 Liquid Nitrogen Tank Explosion 2. Incident 5.3.1.2 Gas Cylinder Cap Removal

  23. Hazards of Gas Cylinders and Liquid Tanks Gases are used in chemistry labs as: reactants, inert atmospheres, carriers, fuel, etc... Almost always purchased as gas cylinders under high pressure Nitrogen and Helium can be purchased stored as cryogenic liquids Beyond hazards of the chemicals, compressed gas cylinders have other hazards High Pressure Gases: typical pressure of gas cylinder = 2200psi = 150atm

  24. Sudden release of high pressure gas can be violent and dangerous High temperature leads to higher pressure (PV = nRT) Most cylinders have a “relief valve” that melts/ruptures at certain T/P Prevents explosions Provides an escape for the gas to lower the dangerous pressure buildup Valve on the Cylinder is its most vulnerable point Will leak or not work if damaged If broken off, the cylinder can become a rocket Asphyxiation Hazards Rapid release of a gas can displace O2 from the room 21% normal, 16%--10% various symptoms, 10% unconscious, 6% death Evacuate a gas leaking area Don’t become a second victim by trying to rescue someone without help Most labs have very good ventilation (fume hoods); confined spaces dangerous Flammable, Corrosive, Toxic, and Reactive Gases All of the normal hazards and safety precautions exist with gases in cylinders Store incompatibles separately (oxygen/flammables) http://www.youtube.com/watch?v=ejEJGNLTo84

  25. Cryogenics (more later) Liquid Nitrogen = 77 K Liquid Helium = 4 K Direct skin contact can result in frostbite and permanent damage Liquid changes rapidly to gas form: pressure and asphyxiation hazards Gas Cylinder Regulators Main tank valve gives you the gas at whatever pressure is inside the tank Regulator = reduces the pressure and lets you adjust to desired pressure Materials in the regulator must be compatible with the gas (HCl = corrosive) Compressed Gas Association Number (CGA) tells what regulator useful for

  26. Brass is commonly used for non-corrosives: soft enough to seal well Different threadings (normal, reverse) female/male attachments, sizes are used i. Keeps you from mixing gas from a cylinder with what’s left in regulator Oxygen mixed with Methane would explode Don’t grease or oil regulators: they can be oxidized Don’t use teflon tape on threads: it is the ends that are making the seal anyway Caps can be tough to remove Don’t stick anything into the cap, you might damage the valve inside Use a designed cap tool or a pipe wrench that only touches outside of cap Use the proper wrench to tighten the regulator to the main tank valve Regulator control valve will turn counterclockwise to close Regulator outlet valve will turn clockwise to close Outlet Valve Control Valve

  27. Securing Cylinders Never leave a gas cylinder unsecured: falling make rupture, or knock off valve Tank straps, chains, bench brackets, floor stands, wall brackets all are used to secure If chaining multiple cylinders, keep chain tight over top third of cylinders Store cylinders in dry, well-ventilated area away from heat, electricity, mechanical Temperature must not get too hot (<125oC) for storage: outside ok if covered No Smoking and No Open Flames signs should be apparent in cylinder area Cylinders must be upright Moving Gas Cylinders Must use a cart specifically designed for the purpose Always secure with a chain or strap prior to moving cylinder Always remove the regulator and put on the cap before moving Don’t “roll” cylinders; use a cart instead

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