Chapter 5: Physical Hazards (continued)
G. Section 5.3.2 Peroxides
1.
Incident 5.3.2.1 Rotary Evaporator Explosion
2.
Peroxides are Potentially Explosive: R—O—O—R or R—O—O--H
a. Some compounds can react with O2 to form explosive peroxides
b. This is most likely to happen upon long-term storage in non-airtight situations
c. Shock, friction, and heat can cause peroxides to decompose violently
1
3. Peroxides: Where do you find them?
a. Some reactions require the use of peroxides, which can be purchased or made
b. Safety precautions are generally understood
c. Biggest danger is contamination of other compounds by peroxides forming in them
d. Ethers are the most notorious Peroxide Forming compounds, but many others exist
a. Diethyl Ether and THF are ubiquitous solvents
b. They aren’t all that reactive, but there is so much of them around
2
4. Preventing Dangerous Peroxide Situations—AVOIDING PEROXIDES
a. Use Inhibitors—chemicals added by manufacturer to prevent peroxides forming
i. Iron inhibits peroxide formation in diethyl ether: often sold in steel can
ii. BHT = Butylated HydroxyToluene: steric hindrance stops ROOR formation
5.
b. Limit Use and Storage
i. Don’t buy or store more than 3-month supply
ii. Test non-inhibited compounds monthly (buy inhibited ones)
Starch-Iodide Paper turns yellow (some ROOR) or black (lots of ROOR)
iii. Store in amber bottle, in cool and dark place
c. Use Alternate Solvents—when chemically feasible
Working with Peroxides
a. Labeling: date received, date opened, date to discard (table above for discard times)
b. Suspect: old chemicals should be tagged and referred to safety officer
c. Detect: Iodide tests, Commercial Test Strips are better but expensive
d. Limit Distillation or Evaporation: don’t go to dryness (stop at 20% volume)
e. Avoid Contamination: returning solvents to bottles (oxidized)
3
6. Managing Peroxide Contaminated Chemicals
a. Emergency Response Actions
i. Don’t disturb the bottle—it’s been there a long time, probably ok a bit longer
ii. Look into liquid—crystal formation indicates peroxides
iii. Get help immediately if crystals are present: bomb squad may need to dispose
b. Decontaminating Peroxide-Containing Solvents
i. Published methods exist, but none are without danger
ii. Probably best to discard properly, and get a new bottle
H. Section 5.3.3 Reactive and Unstable Chemicals
1.
Incident 5.3.3.1 Flaming Glovebox
4
2. Exploding Compounds
a. Explosions don’t happen often, but often enough to take precautions
b. Chemists use reactive compounds because they are reactive
c. Need to be able to predict what compounds will be particularly hazardous
d. Explosion = rapid chemical reaction that burn, deflagrate, or detonate
a. Deflagration = subsonic combustion that usually propagates through thermal
conductivity (hot burning material heats the next layer of cold material and
ignites it). Most “burning” in everyday life.
b. Detonation = supersonic and propagates through shock compression
- Blast wave may move up to 28,000 ft/sec
- Pressure may reach 4,000,000 lbs/sq. inch
- Shrapnel from breaking containers will fly
3. Recognizing Explosive Compounds: certain functional groups are notorious
a. Bretherick’ Handbook of Reactive Chemical Hazards is particularly useful
5
6
b. Self-Reactive = term for explosive compounds
i. Weak bonds decompose to form products with strong bonds
ii. Small amount of activation energy required: heat, shock, friction, spark
c.
General types of explosive compounds
i. High N or O content forming strong NN, O=C=O, H2O bonds in products
ii. Finely divided powders (dust clouds): large surface area for reaction
iii. Very dry compounds are more dangerous: perchlorate salts of organics
iv. Picric Acid and Sodium Azide are well-known explosive hazards
4. Predicting Explosive Properties: explosive if compound contains its own oxidizer!
a. “Zero Oxygen Balance” = contains own O needed to oxidize other elements
b. Ethylene Glycol Dinitrate example
7
5. Minimizing Explosions with Unstable Compounds
a. Recognize that you are working with an unstable compound
b. Replace with a more stable compound (if possible)
c. Control the rate of reaction
i. Use low concentrations: 10% (by mole) solutions or less are recommended
ii. Keep Cold: 10 oC increase doubles the rate of reaction (rule of thumb)
- Monitor the temperature
- Use cold baths: many exist (N2(l), CO2(s) and slurries of both)
- Add reactants dropwise rather than all at once
iii. Scale up carefully and only if essential: harder to control temperature
d. Prudent Practices: fire extinguishers, safety showers, safety shields, “empty” hood
I.
Section 5.3.4 Low- or High-Pressure Hazards
1. Incident 5.3.4.1 Filtration Implosion
8
2. Pressure in the Lab
a. Often necessary and convenient way of accomplishing a goal
b. Often uses glass containers: cheap, unreactive, insoluble, but can break
i. Common glass = soda-lime glass (SiO2, CaO, Na2CO3); shatters with DT
ii. Borosilicate glass (B2O3 added) = much better Temperature tolerance (Pyrex)
c. High pressure is particularly dangerous: get advise from experienced chemist
3. Sealed Tubes
a. Reactants sealed in tube and heated: pressure builds up in the closed system
b. Used when reaction at lower pressures/temperatures don’t work
c. Specially made, thick walled glass tubes are available
d. Glassblowing can be used to seal the tube, or teflon screw tops can be used
e. Don’t fill more than half-full: may become over-pressurized
f. Special tube ovens, or oil bath with shielding is used to heat
4. Hydrogenators
a. R2C=CR2 + H2(g) -----> R2HC—CHR2
b. Increasing H2 pressure may be needed to work
c. Catalyst often used, may be flammable in air
d. Metal jacket over glass, or metal reactor used
e. Run in a hood with appropriate shielding
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5. Vacuum Systems—Low Pressure Hazards
a. Vacuum pumps are common in the lab—rotary evaporators, schlenk lines, filtration
b. Glass under vacuum can “implode”—pressure difference limited to 1 atm
c. Vacuum Exhaust is a source of Toxicant Exposure
i. Vent vacuum pumps into a hood if possible
ii. Traps freeze out vapors before they make it to the pump: N2(l), ROH/CO2(s)
d. Always wear goggles, provide shielding for vacuum line if possible (in hood)
e. Use proper glassware: roundbottom flasks, not flat sided glassware
f. Vacuum Desiccators should be wrapped with tape to prevent glass shards
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J.
Section 5.3.5 Electrical Hazards
1.
Incidents of Electrical Hazards
2.
Basic Electrical Concepts: V = IR
a. Electricity = electrons flowing through a conducting material
b. Current (I) = number of electrons flowing per unit time [1 Amp = 6 x 1018 e-/s]
c. Potential (V) = drive or push on flowing electrons [1 Volt = 1 J/ 1 Coulomb]
i. like water pressure
ii. Greater potential, more powerful are the moving electrons
d. Resistance (R) = how difficult it is for electrons to flow through the material
[ 1 Ohm () = 1 Volt / 1 Amp]
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e. Conductors have low resistance (e- flows): metals, water solutions of salts
f. Insulators have high resistance (no e- flows): rubber, plastic, ceramic, glass
g. Circuit: connected loop of conducting material; no current flows if broken
i. Switches are used to open/close circuits
ii. Interrupting a circuit will stop the flow of electricity
h. Ground: wires to divert the flow of electrons into the ground if component fails
i. Direct Current (DC): electricity flows in only one direction
j. Alternating Current (AC): flow alternates direction (60 Hz)
3. Hazards from Electricity
a. Human body is a conductor; if you become grounded, current will flow through you
i. If you become part of a circuit, 0.1 A can kill you
ii. Maintain insulation between you and current; wet hands allows greater current
b. Currents and your body
i. Muscles can contract when current flows, making it hard to let go
ii. Most circuit breakers are 15 Amps; more than enough to kill
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4. Preventing Electrical Shock
a. Circuit Breaker: protects equipment from over-currents
b. Fuse: protects equipment from accidental grounding
c. Ground Fault Circuit Interrupter (GFCI): protects people
i. Detect wrong path to ground
ii. Breaks the circuit before injury can occur
iii. Required near sinks or other water sources
d. Common ways to get shocked
i. Improperly wired or grounded equipment
ii. Not using GFCI’s
iii. Damaged electrical cords: inspect cords as you use
iv. Modified plugs or 2-prong adapters (which don’t have a ground wire)
e. Use UL (Underwriter’s Laboratory) certified equipment
f. Avoid use of “Homemade” electrical equipment
g. Use and Store Power Strips Appropriately
a. Don’t put a power strip inside a hood: not spark-proof; will ignite solvents
b. Don’t overload power outlets: do they get hot?
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K. Section 5.3.6 The Dangers of Messy Labs
1.
Incident 5.3.6.1 Acids Stored on the Floor
When does “Messy” become “Un-Safe”
a. Need to have room to work without
knocking things off
b. Need to have room to put stuff in sink
without breaking glassware in it
c. Hood can’t be so full someone would
choose to do reaction somewhere else
d. Can’t block exits with junk
e. Can’t hide or obstruct safety equipment
3. Why are academic research labs messy?
a. Students aren’t safety trained
b. Faculty don’t spend much time there
c. Many different people use same lab
d. Sporadic activity promotes Productivity > Safety
2.
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4. Effects of a Messy Lab
a. Common housekeeping issues in a busy lab
i. Unused volatile solvent in an uncovered/unlabeled beaker-FIRE, TOXICANT
ii. Bags, bottles, books on the floor-TRIP HAZARD, CONTAMINATION
iii. Dirty glassware is unwashed-TOXICANT, BROKEN GLASS
iv. Spills near balance are not cleaned up-TOXICANT, REACTIVE
b. What if the lab housekeeping is better?
i. 20% increase in housekeeping efficiency = 15% fewer injuries
ii. Better morale by the people who use the lab
iii. 46% of injuries were associated with poor housekeeping
c. Keeping Labs Safe through Better Housekeeping
i. Benchtops are not for long term storage; they won’t be completely clear, but
make sure items not in current use aren’t left out permanently
ii. Benchtops and Hoods need to be clear enough for regular, safe use
iii. Floors and exits must be clear
iv. Clean glassware as soon as possible. Cluttered sinks mean no glassware is
clean for use and are difficult to use if you need them.
v. Waste needs disposed of in a timely manner, not stored in hoods.
vi. Label all reagents, solutions, and products.
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L. Section 5.3.7 Non-Ionizing Radiation, Electric, and Magnetic Fields
1.
Incident 5.3.7.1 UV Light Exposure
2.
The Energy of the Light Determines the Hazard
a. Non-Ionizing radiation = can’t produce ions when interacting with matter
b. E = hn = hc/l (h = 6.626 x 10-34 J·s) (c = 3.00 x 108 m/s)
16
3. Extremely Low Frequency (ELF) and Very Low Frequency (VLF) Radiation
a. 3-30,000 Hz radiation is rarely used in the lab and is not known to be hazardous
b. All exposed to low background (AC 60Hz); some concerns have been raised
4. Radiowaves: 30 kHz to 300 MHz
a. Used mostly in NMR (Nuclear Magnetic Resonance) instruments, 60-600 MHz
b. No safety concerns associated
5. Microwaves: 1.6-30 GHz
a. EPR (Electron Paramagnetic Resonance) instruments most common use
b. Microwave spectroscopy concerned with rotational energy levels
c. Microwave heating for synthesis (2.54 GHz), easily shielded; not a safety concern
6. Infrared and Visible Light: 1mm-750nm wavelength
a. IR spectrometers and UV-Vis spectrometers are common in labs
b. Lasers are extremely bright and can cause damage (more later)
7. Ultraviolet Radiation
a. UV lamps used to visualize chromatograms or to kill bacteria
b. Can damage eyes and skin; need to wear safety glasses, gloves, etc…
c. Often used in homemade devices where proper shielding hasn’t been done
d. Damage depends on wavelength and exposure time
a. Shortwave (254 nm) and Longwave (365 nm) are common in lab devices
b. 270 nm is maximum for eye damage
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8. Electric and Magnetic Fields
a. Earth’s magnetic field = 0.3-0.7 Gauss
b. NMR: 71,000—14,000 Gauss (300 MHz-600 MHz) common magnetic fields
c. New NMR’s are actively shielded, keeping “5G” magnetic field inside the dewar
d. MRI (magnetic resonance imaging) uses 10,000—30,000 G fields
e. Pacemakers and metal implants may be effected
f. Credit cards/ID cards with magnetic strips can be effected
M. Section 5.3.8 Ionizing Radiation
1.
Incident 5.3.8.1 Plutonium Spill
2.
Ionizing Radiation = capable of producing ions when interacting with molecules
Much more hazardous than non-ionizing radiation of the last section
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3. Types of Radiation: Waves, Particles, and Both
a. Radioactive materials were known to give off something hazardous
b. Names were assigned to unknown particles/rays with different properties
a. a-particle = helium nucleus (2 protons and 2 neutrons)
b. b-particle = electron
238
234
4
0
U

Th

He

2
92
90
2
0g
c. g-ray = high energy light
d. X-ray = high energy light
234
234
0
Th

Pa

90
91
-1 e
e. Neutrons are also given off
4. Radioactive Decay follows First Order Kinetics
a. Half-Life is constant
b. Can be used to date ancient objects based on Carbon-14 (Half-Life = 5730 years)
14
6
C 
14
7
N 
0
-1
e
19
5. Radioactive Hazards in the Lab
a. Radioactive isotopes are used as tracking labels and for imaging (3H = tritium)
b. X-rays and Neutrons are used in X-Ray Diffraction and Neutron Scattering
c. Medical Uses
Radiotracers = radioactive nuclides introduced to an organism to follow pathway
» Iodine-131 is used to diagnose thyroid gland problems
» Thallium-201 and Technetium-99 diagnose heart damage
PET scan = Positron Emission Tomography
d. Radiation from Natural Sources causes damage, but is constantly repaired
e. High doses of radiation—can’t be dealt with by normal repair mechanisms
6. Effects of Radiation
a. Damage to organisms
i. Somatic damage = damage to the organisms itself (sickness or death)
ii. Genetic damage = damage to genetic material (offspring are effected)
b. Factors controlling radiation effects
i. Energy of the radiation: higher energy = more damage (1 Rad = 0.01 J/kg)
ii. Penetrating ability: g-ray > b-particle (1cm) > a-particle (stopped by skin)
iii. Ionizing ability: removing electrons; a-particle >> g-ray
iv. Chemical properties: Kr-85 inert, excrete quickly; Sr-90 replaces Ca, stays
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7. REM = Roentgen Equivalent for Man = normalizes radiation effects for different types
of radiation exposure
8. Models for radiation exposure damage
a. Linear model: any exposure is bad, minimize all exposures
b. Threshold model: no damage unless a certain amount of exposure occurs
c. Better safe than sorry: we don’t know which model is correct, follow linear
9. Working with Ionizing Radiation
a. Minimize the amount of radioisotope used
b. Maximize the distance to the isotope (radiation decrease as square distance)
c. Minimize the amount of time you are in contact with the radioactive isotope
d. Use shielding when possible (lead is good)
e. GET SPECIALIZED TRAINING PRIOR TO USE (REQUIRED)
N. Section 5.3.9 Cryogenic Hazards
1.
Incident 5.3.9.1 Exploding NMR Tube
2.
Cryogens: liquid or solid below 200K, -73oC, or -100oF
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3. Hazard of Using Cryogens
a. Contact with skin can cause Frostbite
i. Skin may stick to cryogenically cooled surface, and tear if removed
ii. Infection, Edema, Blood Clots may result from Frostbite
b. Explosions can be caused by Cryogens Expanding
i. They all turn into gases as warmed
ii. Sealed containers become bombs (CO2 fire extinguisher is rare case)
c.
Asphyxiation can occur if warmed cryogen gas replaces Oxygen
d. Explosions can occur due to liquification of Oxygen in the air
i. Oxygen liquefies at 90K; Liquid N2 is 77K
ii. Any leak in a liquid N2 cooled system will condense liquid O2
iii. Liquid oxygen contact with organic solvents can explode
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4. Handling Cryogens
a. Dewar flasks are double layered and under vacuum in between—vacuum insulation
i. Often made of glass, and can implode if broken—wrap with tape
ii. Silver coating minimizes heat transfer by radiation
b. Dewar lids are not air-tight, so vaporizing cryogen gas can escape—never seal
c. Use tongs if you need to put in/take out something from the cryogen—don’t touch
d. Use a cart to move large dewars—avoid spills, splashing
e. Large storage dewars are made of stainless steel
f. Transfer of cryogen from commercial tank
a. Cryogen is under pressure from vaporization: may “hiss”
b. Use Phase Separator to reduce splashing
c. Transfer in well ventilated room; Buddy System
d. Lots of vaporizing cryogen can asphyxiate
e. Only move a large tank with the proper cart
5. Cryogen Safety Measures
a. Get specialized training from experienced people
b. Prevent direct skin contact—gloves, lab jacket, etc…
c. Always wear goggles: splashing and explosion hazard
d. Avoid asphyxiation hazards with good ventilation and a buddy
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O. Section 5.3.10 Runaway Reaction
1.
Incident 5.3.10.1 and 5. 3.10.2 Runaway Reflux and Runaway Grignard
2.
Runaway Reactions are Common
a. Runaway Reaction: reaction goes too fast, generating heat and boiling solvent
i. Heat generated by exothermic reaction exceeds cooling measures
ii. Heat increases the rate of reactions, so a feedback loop is established
iii. Reaction rate doubles every 10 oC (rule of thumb)
iv. Liquids can vaporize; reagents/products can decompose: gas expansion
explosions can occur, perhaps with an accompanying fire
b. Scale of reaction is important
i. Most reactions are small scale and heat release is dealt with by cooling/stirring
ii. Scaling up successful reactions is a major source of runaway reactions
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3. Predicting Runaway Reactions
a. Check Bretherick’s Handbook of Reactive Chemical Hazards
a. Grignard Reactions
b. Nitrobenzene production from nitric and sulfuric acid and benzene
c. Polymerization of phenol and formaldehyde to form resins
b. Think about how much heat and gas will be produced: calculations ok
c. Carefully review the literature: C&EN News (ACS Chemistry Magazine)
d. Ask more experience chemists about new reactions
4. Learning from Industrial Experience
a. Understand the chemistry of your reaction
b. Control the temperature
c. Add reagents slowly and properly
d. Adequate stirring is essential
e. Follow established procedures
f. Scale up reactions incrementally and take extra precautions
P. Section 5.3.11 Hazards of Catalysts
1.
Incident 5.3.11.1 Catalyst Fire
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2. Catalysts in the Lab
a. 60-90% of industrial chemical process use catalysts
b. Few lab reactions use them, but some very common reactions require them
c. Hydrogenations often require catalyst
a. Raney Ni, Pd/C catalysts
b. Part of the NRC’s Dirty Dozen
c. Pyrophoric in air—catch fire easily
d. Raney Nickel
a. Nickel-Aluminum alloy reacted with NaOH dissolves Al, leaving porous Ni
b. High surface area—catalyzed reaction happens on the Surface
c. Can store high volume of H2 (reactant from hydrogenation)
e. Palladium on Carbon (Pd/C) [Pt, Rh, Ru also used]
1. Precious Metal is dispersed on activated carbon (high surface area)
2. Used in catalytic converters to convert exhaust to safer products
3. Safety Precautions
a. Must handle under an inert atmosphere—Nitrogen or Argon gas
b. Stored as a slurry in water
c. Purge reaction solution with inert gas before introducing catalyst
d. Keep the recovered catalyst (filtered off of solution) wet and covered with inert gas
e. Organic solvent often used in reaction; wash filter with water and transfer wet
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Safety, Storage, Shelf Life, Handling & Disposal of Pd/C
http://www.preciouscatalyst.com/safety_storage.htm
Activated Carbon based powder and paste catalysts are commonly used in liquid phase reactions. The Catalysts in paste from (50-60%
moisture) should be preferred when the presence of water in the process is not detrimental. Moreover, handling paste is much simple
as it reduces dusting and loss of precious metal.
Pd / C can cause fire when dry mixed with Methanol. For reactions using Methanol as solvent, first mix the Catalyst with water to form a
paste before charging the catalyst along with methanol into the reactor.
Pd/C does not catch fire on its own but when in contact with Hydrogen gas and air together it not only catches fire but can explode as
well. Hence, storage should be done in an environment devoid of Hydrogen. Take special care of this aspect even while opening the
packets of the catalyst.
Pd/C can catch fire due to static charge generated due to abrasion of dry catalyst powder with plastic bag (container) during transfer of
catalyst from its plastic bag into the reactor. Therefore, do not empty out the bag into the reaction vessel at once with force. Add slowly.
During filtration and thereafter, do not allow spent catalyst to dry due to vaporization of solvent. Wash the catalyst with D.I. water after
solvent removal. Pack and transport in wet cake form for disposal (either by recovery of Pd metal, its refining and reformulation into
fresh catalyst or for sale of spent material.)
In the event of fire, contain it by pouring water. After fire has been put off, collect all the wet residues manually and pack the same in a
plastic bag and send it to Vineeth for recovery of Palladium metal and consequent conversion into fresh catalyst.
Inhalation of catalyst powder can cause irritation of the respiratory tract. Therefore use mask while handling this product.
In case of powder particles coming into contact with skin or falling into eyes, wash the affected part of the body or eyes profusely with
water.
Shelf Life : Three months from the date of manufacture, if stored in an environment where temperature is maintained below 300C.
Disposal : Immediate arrangements should be made to send back the spent catalyst to the manufacturer for reprocessing. The Catalyst
for disposal should be washed with water to reduce the organic content to a minimum and send off for metal recovery in a water wetted
condition.
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