Chapter 5: Physical Hazards Section 5.1.1 Introduction to Corrosive Hazards

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Chapter 5: Physical HazardsA. Section 5.1.1 Introduction to Corrosive Hazards

1. Incident 5.1.1.1 Sulfuric Acid Spill

2. Corrosives Destroy Skina. Corrosive = chemicals that cause injury by damaging/destroying tissue on exposureb. Can be solids, liquids, gases, or solutionsc. Limit Exposure: goggles, gloves, lab coatd. Use bottle carriers when transporting: rubber containers to prevent breaking bottlese. Know location of/how to use eye wash station and safety showerf. Use fume hood for corrosive gases: concentrated HNO3, HCl fume

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3. Safe Handling of Acidsa. Corrosiveness of Acids is Variable

i. Depend on: structure, tissue exposed, concentration, duration, temperatureii. Use low concentrations and low temperatures if possibleiii. Wash off immediately to lower duration of exposure

b. Strong Acids in Introductory Labs: HCl(aq) -------> H+(aq) + Cl-

(aq) (100%) i. Use HCl if you need H+ and don’t mind Cl-

ii. 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

iii. HNO3 is the most toxic of these acids- Strong oxidizing agent- Produces toxic NOx gases

c. Concentrations > 1M are usually corrosivei. Damage proteins by forming “coagulum”ii. Coagulum may block further damage to underlying tissuesiii. Acids may be less damaging than bases due to this

d. Concentrated Acids = as much as can dissolve in water, usually how purchasedi. Dilute acids using the “A & W Rule”: pour acids into waterii. Opposite procedure may cause acid to boil and splash on you

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4. Safe Handling of Basesa. NaOH (caustic soda; lye); KOH (caustic potash, lye); NH4OH (mostly NH3)b. NaOH and KOH are white solid pellets

i. Strong Bases: NaOH(aq) -------> Na+(aq) + OH-

(aq) (100% dissociation)ii. Caustic in solid form or liquid solutions (Caustic = Corrosive)iii. Generates a lot of heat when you dissolve the solid in wateriv. Can absorb water from air or your hand and make a concentrated solution

c. Aqueous NH3 is a weak base: NH3(aq) + H2O(l) NH4+

(aq) + OH-(aq) (~0.1%)

i. Still corrosiveii. Releases NH3 gasiii. Irritating to eyes/membranes

d. Damage to Tissuesi. May not be immediately painful like an acidii. Saponification of lipids damages the molecules in skin: slick feel; makes soapiii. No protective layer is formed, so base will continue to damage deeper

0.016 M

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5. Eyes and Corrosivesa. Eyes aren’t affected in pH 3-10 rangeb. Eye’s epithelium is rapidly destroyed outside this pH range (strong acid/bases)c. Sulfuric Acid is particularly corrosive due to dehydrating effect and heat releasedd. Every second counts in washing the corrosive away if it contacts your eyee. Wash with water in eye wash station for at least 15 minutesf. Immediately get to an ER for evaluation by a doctor

6. Inhalation of Corrosives: USE FUME HOODS!a. Corrosive gases can be inhaled, or even formed from other gases in the lungs

b. NO2(g) + H2O(l) -------> HNO3(aq)

c. Vapor pressure of NH3(g) over 6M NH4OH is 0.1atm = 100,000ppmd. IDLH value for NH3 is 300ppm (IDLH = immediately dangerous to life or health)e. LClo for 5 minutes exposure for mammals is 5000ppm

7. Oxidizing Agents: very reactive with tissues; react to oxidize your biomoleculesa. HNO3 (and NO3

- salts) strong oxidizers as well as strong acid (corrosive)b. HOOH (hydrogen peroxide): 3% = disinfection; 30% = corrosive, strong oxidizerc. KMnO4 (potassium permanganate) = purple solution; indicator; corrosive/oxidizing

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B. Section 5.2.1 Corrosives in Advanced Labs1. Incident 5.2.1.1 Triflouroacetic Acid-HF Burn

2. The Chemistry of Corrosive Compoundsa. Oxidation/Reduction reactions with Nitric Acid

i. HNO3 has N at the +5 oxidation state and Cu(s) is at 0 oxidation stateii. NO2 has N at the +4 oxidation state (reduced) and Cu2+ is at +2 (oxidized)

b. The oxidizing power of the oxidizer is influenced (raised) by higher concentration

c. Aqua Regia = 3:1 mixture of concentrated HCl and HNO3: will even dissolve goldd. Other acids are corrosive power due to high [H+] concentrations

i. Proteins are destroyed (cut into pieces)ii. Other organic molecules are also destroyed or modified

e. Bases catalytically cleave proteins and esters in fats by hydrolysis reactions

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3. Acids Common in Advanced Labsa. Acetic Acid

i. Can be purified as “Glacial Acetic Acid” (fridge freezes 16.7oC to white solid)ii. Flammable at concentrations > 50%iii. Strong Dehydrating Agent: enough heat generated to cause burnsiv. Volatile and vapors can cause damage to lungs

b. Phosphoric Acid (H3PO4)i. Weak acid, but can be found pure (not in water solution)ii. Strong corrosive and causes severe burns to skin in concentrated formsiii. Is irritating to the lungs, but usually does not cause pulmonary edema

c. Hydrofluoric Acid (HF)i. Weak acid in water, yet highly corrosive if > 0.01 Mii. If exposed, flush with water for only 5 minutes, then get medical help quickiii. Calcium Gluconate or Benzalkonium Chloride are antidotes for burnsiv. Don’t work with HF unless the agents are available in the labv. Many famous Fluorine Chemists (use HF) are missing fingers!

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4. The Halogens: Oxidizing Agents (F2, Cl2, Br2, I2)a. Reaction: X2 + 2e- -------> 2X- b. F2 is exceptionally dangerous and can oxidize almost anything (rarely used)c. Cl2 was the first Weapon of Mass Destruction; Chemical Weapon in WWI

i. 1000ppm airborne concentration (0.001 atm) for a few breaths is fatalii. Greenish colored gas released by artillery shells

d. Br2 is a volatile (175 mm Hg vapor pressure) brown liquidi. Painful and destructive upon contact with skin or eyesii. Lachrymator (tears) at around 1ppm; Fatal at 1000ppm

e. I2 is a purple volatile solid (0.3 mm Hg)i. Disinfectant to sanitize waterii. Brown 8% concentration in ethanol “tincture of iodine” used to clean woundsiii. Vapor is irritating and mildly corrosive; can be fatal at high concentrations

5. Phenol: complex toxicant behavior from a simple moleculeiv. Corrosive, toxic, rapidly absorbed through skinv. Local anesthetic: can’t feel it burning you (might smell it: 0.06ppm odor)vi. Chloraseptic = 1% solution has antiseptic properties

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6. Other Dehydrating Agents and Water Reactive Compoundsa. Sodium: Na + 2H2O -------> 2 NaOH + H2 (flammable)b. NaH (Sodium Hydride), LiAlH4 (Lithium Aluminum Hydride)

i. Common Reducing Agentsii. Produce H2 (flammable) and are corrosive

c. Drying Agents: used to remove water from organic solvents (after extraction)i. Reactive with waterii. CaO, P2O5 (P4O10) react strongly with water and become corrosive

d. Response: scrape off any solid, wash with plenty of water, seek medical attention

7. Working with Corrosivesa. Wear gloves and lab coats to cover skinb. Nitrile gloves are generally effectivec. Clean up spills:

i. Keep others awayii. Report the spill to instructorsiii. Use an appropriate spill kit

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C. Section 5.1.2 Flammables1. Incident 5.1.2.1 Sodium-Solvent Fire

2. Using Flammablesa. Everyday use: gasoline for your car and propane for you grillb. Very useful in the lab as wellc. Flammable Chemical = easily ignite and rapidly burn, release much heat

i. Once ignited, they will burn until all of the fuel is goneii. Come in gases, liquids, and solids: most often solvents for reactionsiii. Common: Acetone, Ethanol, Diethyl Ether, Ethyl Acetate, Hexane, Toluene

d. Combustibles: ignite slower, but burn readily

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3. Characteristics of Flammables and Combustiblesa. Boiling Point is usually relatively low (temperature gas in equilibrium with liquid)b. Flash Point = lowest temperature vapor near surface can be ignitedc. Autoignition Temperature = temperature of spontaneous ignition (not usual in lab)d. Flammability Limits = range of vapor concentrations which supports fire/ignitione. Lower Explosive Limit (LEL) = lowest % by volume required for explosionf. Upper Explosive Limit (UEL) = highest % by volume to support fire (need O2)g. LEL (1-4%) and UEL (6-20%) common (Acetylene 2.5%--81%, very dangerous)

4. Fire Hazard Rating System: different numbers, but SAME INFORMATION TO YOUa. United Nation’s Globally Harmonized System (GHS) uses chemical properties

b. National Fire Protection Association (NFPA) uses the opposite order of numbers

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5. Review of How Fires Burna. Fire Tetrahedron: all parts needed for fireb. Remove any of the four, fire will go outc. If using a flammable solvent:

i. Search for and remove sources of ignition- Bunsen burner going- Sparks from electrical sources- Sparks from pouring from metal containers (Static electricity)

ii. It’s the vapors that burn, not the liquid- Vapors from spill can catch fire- Work in a hood to remove vapors

iii. Recognize the Flammable Solvent- Ether: particularly dangerous; Low Flash Point- Compare to common fuels

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6. Chemical Structure and Flammabilitya. Methanol (CH3OH) vs. Dichloromethane (CH2Cl2)

i. Carbon in methanol has 3 H’s which can be replaced by oxygen (oxidation)ii. CH2Cl2 only has 2 H’s left to react (less reactive toward oxidation = burning)iii. Similar size and volatility

b. CH3OH vs. CH3CH2OH vs. CH3CH2CH2OH vs. CH3CH2CH2CH2OHi. 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 Explosion1. Incident 5.2.2.1 Ether Fire

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2. Fires are Chemical Reactionsa. Oxidizable material, plus oxidizing agent (usually O2) makes heat and lightb. Exothermic Reactions = Heat is releasedc. Complete Combustion = fuel is oxidized fully; requires excess O2 d. Incomplete Combustion = fuel is not fully oxidized; O2 is limited

3. Dangers of Firesa. Heat is released

i. Flashover = heat released ignites other material without flames touching itii. Small fire can quickly turn into a large fire if flashover occursiii. Flashover Temps: 480-650 oC (900-1200 oF)iv. CO ignition (609 oC) contributes to flashover

b. Toxic by-products are generated: many new chemicals produced by oxidationi. CO2 = simple asphyxiant; CO = chemical asphyxiant

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ii. Smoke = mixture of gases and particulates; impedes lung functioniii. Gases: HCN, HCl, NOx (particularly from plastics)

c. Consumption of Oxygeni. Physiological function is impaired as the O2 concentration decreases

ii. Usually, smoke inhalation is deadly before death is cause by lack of O2 iii. 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

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4. Lab Gas Supplies and Firesa. Natural gas (methane, CH4) is often plumbed into lab for Bunsen burners, etc…b. Methane is extremely flammable: GHS = 1; NFPA = 4c. LEL = 4.5% and UEL = 16.5%d. Must make sure to turn off all gas valves after use: leak could result in a firee. Odorant gas (ethanethiol, CH3CH2SH) added to alert you f. Many modern labs have a main gas shutoff valve to activate when evacuating a fire

5. Explosions from Firesa. Explosion = sudden release of energy as heat and light

i. Energy released faster than can be dissipated by convection and heat capacityii. Shock wave at supersonic velocity is formed = wave of high pressure gas that

can do considerable damageb. Requires flammable vapors in concentration between LEL and UEL + ignitionc. BLEVE (“blev-ee”) = boiling liquid expanding vapor explosion

i. Container of flammable liquid (solvent) is heated to failure due to pressureii. Rapid release of flammable vapors that are ignited instantlyiii. Sealed bottle in a lab fire: PV=nRT iv. 300K to 1300K, Pressure goes from 1atm to 4.3 atmv. Can autoignite, or be ignited by the fire which caused it to fail

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E. Section 5.2.3 Incompatibles1. Incident 5.2.3.1 Exploding Hazardous Waste

2. A Chemical Overview of Incompatiblesa. Incompatible Chemicals = combination of substances that react violently with

each other to potentially produce explosions and/or toxic substancesb. Often unanticipated reactions occur—we aren’t prepared, may be no one aroundc. Incompatibles at low concentration can be mixed on purpose: we are preparedd. Not possible to memorize all possible combinations of incompatible chemicalse. Fundamental Chemistry can alert us to structures of incompatible partnersf. Most exothermic reactions are acid/base or oxidation/reduction. Ask yourself:

i. Is this a strong acid?ii. Is this a strong base?iii. Is this easily oxidized?iv. Is this easily reduced?

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3. Acid-Base Incompatiblesa. Most common in laboratoriesb. Strong Acid + Strong Base = very exothermic reaction

i. Common Strong Acids: HCl, HNO3, H2SO4, HClO4, HBr, HIii. Common Strong Bases: NaOH, KOH, Ca(OH)2, LiOH, RbOH, CsOH

c. Lower concentrations tend to make the reaction safer: less reactant, more waterd. Other common Acid/Base Incompatible Reactions

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4. Strong Oxidants and Reductants—Redox Incompatiblesa. Must identify compounds that are easily oxidized or reduced

i. Good Oxidizing Agent gets Reduced Easily (large positive Eo)F2 is easily reduced; it is a strong Oxidizing Agent

ii. Good Reducing Agent gets Oxidized Easily (large negative Eo)Li(s) is easily oxidized; it is a strong Reducing Agent

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b. Trendsi. 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)

ii. 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

iii. Anions with multiple oxygens and central atoms at high oxidation states are good oxidizers: ClO4

- (particularly explosive), CrO4-, NO3

-, etc…iv. Organic compounds are often easily oxidized (C is 0, can become +4)

c. Unanticipated Example: HNO3 + CH3COOH (nitric acid + acetic acid) REDOX

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5. Water-Reactivesa. Water is usually non-reactive and safe, but some chemicals react with it violently

b. Alkali metals often used to “dry” organic solvents (on NRC’s Dirty Dozen list)i. When “used up” the drying agent is destroyed using ROHii. If not all used up, or ROH added too quickly, fires can result (esp. w/ solvents)

c. Special techniques in advanced chemistry labs for handling water reactive solutionsi. Glovebox: controlled atmosphere with no water (or O2)ii. Schlenk Line: all operations done under vacuum or inert gas

d. Concentrated H2SO4: very exothermic reaction when mixed with water

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6. Pyrophorics = chemicals that ignite spontaneously in aira. Oxidized by O2 in air or react very quickly with H2O in airb. Some finely divided metal powders: Zn(dust) + H2O(l) -----> Zn(OH)2(s) + H2(g) c. LiAlH4 (on NRC’s Dirty Dozen list)

i. LiAlH4(s) + 4H2O(l) -----> LiOH(aq) + Al(OH)3(s) + 4H2(g) ii. Also purchased in solution of organic solvent (THF or Ether) FLAMMABLE!

d. Boranes (BxHy) are boron equivalents to hydrocarbonsi. Explored as possible rocket propellantsii. Thermodynamic stability of the oxides produced lead to exothermicityiii. B2H6 + 3O2 -----> B2O3 + 3H2O

e. Silanes (SixHy) are silicon equivalents to hydrocarbonsi. Thermodynamic stability of the oxides produced lead to exothermicityii. SiH4 + 2O2 -----> SiO2 + 2H2O

f. Elemental Phosphorousi. Phosphorous only appears as its oxides in nature; we can make elemental formii. The allotrope “white phosphorous” = P4 tetrahedron that reacts with air

P4 + 5O2 -----> P4O10 iii. Stored under water to prevent interaction with oxygen

g. When working with pyrophorics: Know What You are Doing, and Have a Plan

P P

P

P

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7. Storing Incompatiblesa. Incompatible chemicals should not be stored togetherb. This is especially important in earthquake active locationsc. Tornadoes (or other weather) can still end up breaking bottlesd. Minimize the amount of chemicals you store in the lab (of any kind)

F. Section 5.3.1 Gas Cylinders and Cryogenic Liquids1. Incident 5.3.1.1 Liquid Nitrogen Tank Explosion

2. Incident 5.3.1.2 Gas Cylinder Cap Removal

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3. Hazards of Gas Cylinders and Liquid Tanksa. Gases are used in chemistry labs as: reactants, inert atmospheres, carriers, fuel, etc...b. Almost always purchased as gas cylinders under high pressurec. Nitrogen and Helium can be purchased stored as cryogenic liquidsd. Beyond hazards of the chemicals, compressed gas cylinders have other hazards

4. High Pressure Gases: typical pressure of gas cylinder = 2200psi = 150atm

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a. Sudden release of high pressure gas can be violent and dangerousb. High temperature leads to higher pressure (PV = nRT)c. Most cylinders have a “relief valve” that melts/ruptures at certain T/P

i. Prevents explosionsii. Provides an escape for the gas to lower the dangerous pressure buildup

d. Valve on the Cylinder is its most vulnerable pointi. Will leak or not work if damagedii. If broken off, the cylinder can become a rocket

5. Asphyxiation Hazardsa. Rapid release of a gas can displace O2 from the roomb. 21% normal, 16%--10% various symptoms, 10% unconscious, 6% deathc. Evacuate a gas leaking aread. Don’t become a second victim by trying to rescue someone without helpe. Most labs have very good ventilation (fume hoods); confined spaces dangerous

6. Flammable, Corrosive, Toxic, and Reactive Gasesa. All of the normal hazards and safety precautions exist with gases in cylindersb. Store incompatibles separately (oxygen/flammables)

http://www.youtube.com/watch?v=ejEJGNLTo84

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7. Cryogenics (more later)a. Liquid Nitrogen = 77 Kb. Liquid Helium = 4 Kc. Direct skin contact can result in frostbite and permanent damaged. Liquid changes rapidly to gas form: pressure and asphyxiation hazards

8. Gas Cylinder Regulatorsa. Main tank valve gives you the gas at whatever pressure is inside the tankb. Regulator = reduces the pressure and lets you adjust to desired pressurec. Materials in the regulator must be compatible with the gas (HCl = corrosive)d. Compressed Gas Association Number (CGA) tells what regulator useful for

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e. Brass is commonly used for non-corrosives: soft enough to seal wellf. Different threadings (normal, reverse) female/male attachments, sizes are used

i. Keeps you from mixing gas from a cylinder with what’s left in regulatorii. Oxygen mixed with Methane would explode

g. Don’t grease or oil regulators: they can be oxidizedh. Don’t use teflon tape on threads: it is the ends that are making the seal anywayi. Caps can be tough to remove

i. Don’t stick anything into the cap, you might damage the valve insideii. Use a designed cap tool or a pipe wrench that only touches outside of cap

j. Use the proper wrench to tighten the regulator to the main tank valvek. Regulator control valve will turn counterclockwise to closel. Regulator outlet valve will turn clockwise to close

Outlet ValveControlValve

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9. Securing Cylindersa. Never leave a gas cylinder unsecured: falling make rupture, or knock off valveb. Tank straps, chains, bench brackets, floor stands, wall brackets all are used to securec. If chaining multiple cylinders, keep chain tight over top third of cylinders

d. Store cylinders in dry, well-ventilated area away from heat, electricity, mechanicale. Temperature must not get too hot (<125oC) for storage: outside ok if coveredf. No Smoking and No Open Flames signs should be apparent in cylinder areag. Cylinders must be upright

10. Moving Gas Cylindersa. Must use a cart specifically designed for the purposeb. Always secure with a chain or strap prior to moving cylinderc. Always remove the regulator and put on the cap before movingd. Don’t “roll” cylinders; use a cart instead