Chapter 5: Physical Hazards
A. Section 5.1.1 Introduction to Corrosive Hazards
1.
Incident 5.1.1.1 Sulfuric Acid Spill
2.
Corrosives Destroy Skin
a. Corrosive = chemicals that cause injury by damaging/destroying tissue on exposure
b. Can be solids, liquids, gases, or solutions
c. Limit Exposure: goggles, gloves, lab coat
d. Use bottle carriers when transporting: rubber containers to prevent breaking bottles
e. Know location of/how to use eye wash station and safety shower
f. Use fume hood for corrosive gases: concentrated HNO3, HCl fume
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3. Safe Handling of Acids
a. Corrosiveness of Acids is Variable
i. Depend on: structure, tissue exposed, concentration, duration, temperature
ii. Use low concentrations and low temperatures if possible
iii. 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 Clii. 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 corrosive
i. Damage proteins by forming “coagulum”
ii. Coagulum may block further damage to underlying tissues
iii. Acids may be less damaging than bases due to this
d. Concentrated Acids = as much as can dissolve in water, usually how purchased
i. Dilute acids using the “A & W Rule”: pour acids into water
ii. Opposite procedure may cause acid to boil and splash on you
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4. Safe Handling of Bases
a. 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 water
iv. 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 corrosive
ii. Releases NH3 gas
iii. Irritating to eyes/membranes
0.016 M
d. Damage to Tissues
i. May not be immediately painful like an acid
ii. Saponification of lipids damages the molecules in skin: slick feel; makes soap
iii. No protective layer is formed, so base will continue to damage deeper
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5. Eyes and Corrosives
a. Eyes aren’t affected in pH 3-10 range
b. 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 released
d. Every second counts in washing the corrosive away if it contacts your eye
e. Wash with water in eye wash station for at least 15 minutes
f. 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.
c.
d.
e.
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
7. Oxidizing Agents: very reactive with tissues; react to oxidize your biomolecules
a. HNO3 (and NO3- salts) strong oxidizers as well as strong acid (corrosive)
b. HOOH (hydrogen peroxide): 3% = disinfection; 30% = corrosive, strong oxidizer
c. KMnO4 (potassium permanganate) = purple solution; indicator; corrosive/oxidizing
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B. Section 5.2.1 Corrosives in Advanced Labs
1.
Incident 5.2.1.1 Triflouroacetic Acid-HF Burn
2.
The Chemistry of Corrosive Compounds
a. Oxidation/Reduction reactions with Nitric Acid
b.
c.
d.
e.
i. HNO3 has N at the +5 oxidation state and Cu(s) is at 0 oxidation state
ii. 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
i. Proteins are destroyed (cut into pieces)
ii. Other organic molecules are also destroyed or modified
Bases catalytically cleave proteins and esters in fats by hydrolysis reactions
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3. Acids Common in Advanced Labs
a. 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 burns
iv. 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 forms
iii. 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 M
ii. If exposed, flush with water for only 5 minutes, then get medical help quick
iii. Calcium Gluconate or Benzalkonium Chloride are antidotes for burns
iv. Don’t work with HF unless the agents are available in the lab
v. 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- -------> 2Xb. 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 fatal
ii. Greenish colored gas released by artillery shells
d.
Br2 is a volatile (175 mm Hg vapor pressure) brown liquid
i. Painful and destructive upon contact with skin or eyes
ii. Lachrymator (tears) at around 1ppm; Fatal at 1000ppm
e. I2 is a purple volatile solid (0.3 mm Hg)
i. Disinfectant to sanitize water
ii. Brown 8% concentration in ethanol “tincture of iodine” used to clean wounds
iii. Vapor is irritating and mildly corrosive; can be fatal at high concentrations
5. Phenol: complex toxicant behavior from a simple molecule
i. Corrosive, toxic, rapidly absorbed through skin
ii. Local anesthetic: can’t feel it burning you (might smell it: 0.06ppm odor)
iii. Chloraseptic = 1% solution has antiseptic properties
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6. Other Dehydrating Agents and Water Reactive Compounds
a. Sodium: Na + 2H2O -------> 2 NaOH + H2 (flammable)
b. NaH (Sodium Hydride), LiAlH4 (Lithium Aluminum Hydride)
i. Common Reducing Agents
ii. Produce H2 (flammable) and are corrosive
c. Drying Agents: used to remove water from organic solvents (after extraction)
i. Reactive with water
ii. 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 Corrosives
a. Wear gloves and lab coats to cover skin
b. Nitrile gloves are generally effective
c. Clean up spills:
i. Keep others away
ii. Report the spill to instructors
iii. Use an appropriate spill kit
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C. Section 5.1.2 Flammables
1.
Incident 5.1.2.1 Sodium-Solvent Fire
2.
Using Flammables
a. Everyday use: gasoline for your car and propane for you grill
b. Very useful in the lab as well
c. Flammable Chemical = easily ignite and rapidly burn, release much heat
i. Once ignited, they will burn until all of the fuel is gone
ii. Come in gases, liquids, and solids: most often solvents for reactions
iii. 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 Combustibles
a. Boiling Point is usually relatively low (temperature gas in equilibrium with liquid)
b. Flash Point = lowest temperature vapor near surface can be ignited
c. Autoignition Temperature = temperature of spontaneous ignition (not usual in lab)
d. Flammability Limits = range of vapor concentrations which supports fire/ignition
e. Lower Explosive Limit (LEL) = lowest % by volume required for explosion
f. 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 YOU
a. 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 Burn
a. Fire Tetrahedron: all parts needed for fire
b. Remove any of the four, fire will go out
c. 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 Flammability
a. 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. CH3CH2CH2CH2OH
i. 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
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2. Fires are Chemical Reactions
a. Oxidizable material, plus oxidizing agent (usually O2) makes heat and light
b. Exothermic Reactions = Heat is released
c. Complete Combustion = fuel is oxidized fully; requires excess O2
d. Incomplete Combustion = fuel is not fully oxidized; O2 is limited
3. Dangers of Fires
a. Heat is released
i. Flashover = heat released ignites other material without flames touching it
ii. Small fire can quickly turn into a large fire if flashover occurs
iii. 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 oxidation
i. CO2 = simple asphyxiant; CO = chemical asphyxiant
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c.
ii. Smoke = mixture of gases and particulates; impedes lung function
iii. Gases: HCN, HCl, NOx (particularly from plastics)
Consumption of Oxygen
i. 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 Fires
a. Natural gas (methane, CH4) is often plumbed into lab for Bunsen burners, etc…
b. Methane is extremely flammable: GHS = 1; NFPA = 4
c. LEL = 4.5% and UEL = 16.5%
d. Must make sure to turn off all gas valves after use: leak could result in a fire
e. 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 Fires
a. Explosion = sudden release of energy as heat and light
i. Energy released faster than can be dissipated by convection and heat capacity
ii. Shock wave at supersonic velocity is formed = wave of high pressure gas that
can do considerable damage
b. Requires flammable vapors in concentration between LEL and UEL + ignition
c. BLEVE (“blev-ee”) = boiling liquid expanding vapor explosion
i. Container of flammable liquid (solvent) is heated to failure due to pressure
ii. Rapid release of flammable vapors that are ignited instantly
iii. Sealed bottle in a lab fire: PV=nRT
iv. 300K to 1300K, Pressure goes from 1atm to 4.3 atm
v. Can autoignite, or be ignited by the fire which caused it to fail
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E. Section 5.2.3 Incompatibles
1.
Incident 5.2.3.1 Exploding Hazardous Waste
2.
A Chemical Overview of Incompatibles
a. Incompatible Chemicals = combination of substances that react violently with
each other to potentially produce explosions and/or toxic substances
b. Often unanticipated reactions occur—we aren’t prepared, may be no one around
c. Incompatibles at low concentration can be mixed on purpose: we are prepared
d. Not possible to memorize all possible combinations of incompatible chemicals
e. Fundamental Chemistry can alert us to structures of incompatible partners
f. 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 Incompatibles
a. Most common in laboratories
b. Strong Acid + Strong Base = very exothermic reaction
i. Common Strong Acids: HCl, HNO3, H2SO4, HClO4, HBr, HI
ii. Common Strong Bases: NaOH, KOH, Ca(OH)2, LiOH, RbOH, CsOH
a. Lower concentrations tend to make the reaction safer: less reactant, more water
b. Other common Acid/Base Incompatible Reactions
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4. Strong Oxidants and Reductants—Redox Incompatibles
a. 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
ii. Good Reducing Agent gets Oxidized Easily (large negative Eo)
Li(s) is easily oxidized; it is a strong Reducing Agent
i.
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b. Trends
i. 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-Reactives
a. Water is usually non-reactive and safe, but some chemicals react with it violently
a. Alkali metals often used to “dry” organic solvents (on NRC’s Dirty Dozen list)
i. When “used up” the drying agent is destroyed using ROH
ii. If not all used up, or ROH added too quickly, fires can result (esp. w/ solvents)
b. Special techniques in advanced chemistry labs for handling water reactive solutions
i. Glovebox: controlled atmosphere with no water (or O2)
ii. Schlenk Line: all operations done under vacuum or inert gas
c. Concentrated H2SO4: very exothermic reaction when mixed with water
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6. Pyrophorics = chemicals that ignite spontaneously in air
a. Oxidized by O2 in air or react very quickly with H2O in air
b. 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 hydrocarbons
i. Explored as possible rocket propellants
ii. Thermodynamic stability of the oxides produced lead to exothermicity
iii. B2H6 + 3O2 -----> B2O3 + 3H2O
e. Silanes (SixHy) are silicon equivalents to hydrocarbons
i. Thermodynamic stability of the oxides produced lead to exothermicity
ii. SiH4 + 2O2 -----> SiO2 + 2H2O
f. Elemental Phosphorous
i. Phosphorous only appears as its oxides in nature; we can make elemental form
P
ii. The allotrope “white phosphorous” = P4 tetrahedron that reacts with air
P
P
P
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
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7. Storing Incompatibles
a. Incompatible chemicals should not be stored together
b. This is especially important in earthquake active locations
c. Tornadoes (or other weather) can still end up breaking bottles
d. Minimize the amount of chemicals you store in the lab (of any kind)
F. Section 5.3.1 Gas Cylinders and Cryogenic Liquids
1.
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 Tanks
a. Gases are used in chemistry labs as: reactants, inert atmospheres, carriers, fuel, etc...
b. Almost always purchased as gas cylinders under high pressure
c. Nitrogen and Helium can be purchased stored as cryogenic liquids
d. 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 dangerous
b. High temperature leads to higher pressure (PV = nRT)
c. Most cylinders have a “relief valve” that melts/ruptures at certain T/P
i. Prevents explosions
ii. Provides an escape for the gas to lower the dangerous pressure buildup
d. Valve on the Cylinder is its most vulnerable point
i. Will leak or not work if damaged
ii. If broken off, the cylinder can become a rocket
http://www.youtube.com/watch?v=ejEJGNLTo84
5. Asphyxiation Hazards
a. Rapid release of a gas can displace O2 from the room
b. 21% normal, 16%--10% various symptoms, 10% unconscious, 6% death
c. Evacuate a gas leaking area
d. Don’t become a second victim by trying to rescue someone without help
e. Most labs have very good ventilation (fume hoods); confined spaces dangerous
6. Flammable, Corrosive, Toxic, and Reactive Gases
a. All of the normal hazards and safety precautions exist with gases in cylinders
b. Store incompatibles separately (oxygen/flammables)
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7. Cryogenics (more later)
a. Liquid Nitrogen = 77 K
b. Liquid Helium = 4 K
c. Direct skin contact can result in frostbite and permanent damage
d. Liquid changes rapidly to gas form: pressure and asphyxiation hazards
8. Gas Cylinder Regulators
a. Main tank valve gives you the gas at whatever pressure is inside the tank
b. Regulator = reduces the pressure and lets you adjust to desired pressure
c. 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 well
f. 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
ii. Oxygen mixed with Methane would explode
g.
h.
i.
j.
k.
l.
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
i. Don’t stick anything into the cap, you might damage the valve inside
ii. 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
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9. Securing Cylinders
a. Never leave a gas cylinder unsecured: falling make rupture, or knock off valve
b. Tank straps, chains, bench brackets, floor stands, wall brackets all are used to secure
c. If chaining multiple cylinders, keep chain tight over top third of cylinders
d. Store cylinders in dry, well-ventilated area away from heat, electricity, mechanical
e. Temperature must not get too hot (<125oC) for storage: outside ok if covered
f. No Smoking and No Open Flames signs should be apparent in cylinder area
g. Cylinders must be upright
10. Moving Gas Cylinders
a. Must use a cart specifically designed for the purpose
b. Always secure with a chain or strap prior to moving cylinder
c. Always remove the regulator and put on the cap before moving
d. Don’t “roll” cylinders; use a cart instead
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